A. P. Inkov, Ph.D. tech. Sciences, EKOTERM LLC
Ventilation systems, heating and air conditioning (HAC) must provide optimal conditions microclimate and air environment premises of a hospital, maternity hospital or other hospital. When designing, constructing (reconstructing) and operating EQA systems, you should use the basic provisions of existing special regulatory documents, as well as a number of other documents approved by the Russian Ministry of Health. At the same time, EQA systems for medical and preventive institutions (HCI) in accordance with Russian standards have a number of features compared to others public buildings and structures. Some of them are listed below.
1. In healthcare facilities buildings, the use of vertical collectors for both supply and exhaust systems is not allowed.
2. Air removal from operating rooms, anesthesia rooms, resuscitation rooms, labor and X-ray rooms is carried out from two zones (upper and lower).
3. The relative humidity and temperature of the operating units is maintained constantly and around the clock.
4. In hospital wards, relative air humidity is standardized only for the winter period.
5. In health care facilities, air recirculation is not allowed in EQA systems.
6. The coolant temperature for water heating systems must correspond to the purpose of the building.
7. The sound pressure level from ventilation systems in wards and operating rooms of hospitals should not exceed 35 dBA.
Taking into account the above, it is clear that quality project EQA systems can only be carried out by specialized design organizations that have a library of regulatory documents and certain experience practical work.
Below we will take a closer look at the most difficult design issue. , postoperative wards, resuscitation rooms, intensive care wards, delivery rooms, anesthesia rooms and other rooms classified according to the standards as “OCH” cleanliness category. In these rooms, ventilation and air conditioning are mandatory, and the frequency of air exchange is determined by calculation based on the conditions of heat generation assimilation, but not less than tenfold exchange
(see Table 1 for standards).
Table No. 1. Design temperatures, air exchange rates, categories for cleanliness of premises in medical institutions
It should immediately be noted that the classification of premises according to the degree of air purity adopted in the work is outdated and requires processing in accordance with currently valid regulatory documents.
The new standard was adopted and introduced in Russia on May 18, 2000 and harmonized with the international standard ISO 14644-1-99. This article will use the terms and definitions of this standard, which ranges from ISO Class 1 (highest class) to ISO Class 9 (lowest class) for cleanliness classes.
It is known that long-term stay of patients in ordinary surgical and therapeutic hospitals is dangerous for them. After some time in the hospital, they become carriers of the so-called hospital strains of bacteria and carriers of pathogens of various infections. This also applies to the staff of medical institutions. Methods of preventing and treating infections such as antibiotics, immune and hormonal drugs, wet cleaning of premises with antiseptic solutions, ultraviolet irradiation, etc. do not give the desired effect.
A clean room has a fundamental difference compared to these methods. It is not aimed at combating and destroying existing microorganisms in the room. It does not allow them there, and microorganisms coming from patients or medical personnel are immediately removed from the room by air flow. The purpose of clean operating rooms is to reduce the growth of microbial contamination, primarily in the area of the operating room and instrument tables.
By modern classification operating rooms can be classified as clean rooms (CH) ISO class 5 and higher. The class of a clean room is characterized by a classification number that determines the maximum permissible countable concentration of aerosol particles of a certain size in one cubic meter of air. A particle is defined as a solid, liquid or multiphase object with a size ranging from 0.05 to 100 microns. When classifying emergency situations, non-living particles with a size of 0.1 to 5 microns are considered. A cleanroom may contain one or more clean areas (a clean area may be open or enclosed) and may be located either inside or outside the cleanroom.
According to the standard, a clean room is a room in which the concentration of airborne particles is controlled and which is constructed and operated to minimize the entry, release and retention of particles within the room, and in which other parameters are controlled as necessary, for example, temperature, humidity and pressure.
In accordance with the standard, three temporary phases of the creation and existence of a clean room should be distinguished:
1. As-built: a state in which the cleanroom system is complete, all service systems are connected, but no production equipment, materials or personnel are present.
2. Equipped (at-rest): a state in which the cleanroom system is equipped and debugged in accordance with the agreement between the customer and the contractor, but there is no staff.
3. Operational: the state in which the cleanroom system is functioning in an established manner, with an established number of personnel working in accordance with the documentation.
This above division is of fundamental importance in the design, construction, certification and operation of cleanrooms. The air particle cleanliness of a clean room or clean area must be determined by one (or more) of the three clean room conditions. When designing and constructing medical institutions, we will be most interested in the last, operational state of the emergency.
The air around us contains a large number of both living and non-living particles, differing in nature and size. When determining the air cleanliness class in a clean room, the standard takes into account the concentration of non-living aerosol particles ranging in size from 0.1 to 5.0 microns. When assessing the air cleanliness class of operating rooms important criterion is the number of living microorganisms in it, so this issue needs to be considered in more detail.
The work analyzes the main sources of air micropollutants. Foreign statistical data are presented showing that there is approximately one microorganism per 1,000 suspended aerosol particles. It is said that due to the multiplicity of factors influencing microbial contamination, these data are approximate, probabilistic in nature. But nevertheless, they give an idea of the relationship between the number of non-living particles and the number of microorganisms in the air.
Cleanliness classes for airborne particles for clean rooms and clean areas
To assess the required class of air purity in operating rooms, depending on the volumetric concentration of microorganisms in it, you can use the data in the summary table. 2 standards.
Clean rooms class 5 in table. 2 are divided into two subclasses:
- Subclass A - with a maximum permissible number of microorganisms of no more than 1 (achieved in a unidirectional air flow).
- Subclass B - with a maximum permissible number of microorganisms of no more than 5.
In clean rooms of a higher class (classes 4 to 1), there should be no microorganisms at all.
In order to move on to the consideration of practical issues that are of most interest to designers of HVAC systems, we will once again consider some of the requirements imposed by regulatory documents for emergency ventilation and air conditioning systems. In passing, we note that in addition to the requirements for VC systems, designers must also know and comply with the entire list of other mandatory requirements for emergency situations: requirements for planning solutions, requirements for the design and materials of emergency situations, requirements for emergency equipment, requirements for engineering systems, requirements for medical personnel and technological clothing, etc. Due to the limited scope of this article, these issues are not considered here.
Below is a list of just some of the basic requirements for emergency ventilation and air conditioning systems.
1. The air supply system in emergency situations from class 1 to 6, as a rule, must ensure the organization of air exchange with a vertical unidirectional flow. For class 6 it is possible to use non-unidirectional air flow. The standard provides a definition: unidirectional air flow - an air flow with parallel, as a rule, jets (stream lines) passing in the same direction with the same cross section speed. The terms “laminar” and “turbulent” flow are not recommended to be used to characterize air flows in emergency situations.
2. Air duct coverings and their structures located in clean rooms ah, as well as the coatings of the filter chambers and their structures must allow periodic treatment with disinfectant solutions. This requirement is mandatory for microbial controlled emergencies.
3.
must have automatic temperature and humidity control, locking, remote control, and alarm.
4. In a state of emergency with a unidirectional vertical flow, the number of holes that remove air flows from the state of emergency is selected in accordance with the need to ensure the verticality of air flows.
To the list of the above requirements for ventilation and air conditioning systems operating rooms should also be added:
- Requirement to use multi-stage filtration of air supplied from outside (at least 3 stages) and use as final filters high efficiency class not less than H12.
- The requirement to ensure the required speed of unidirectional flow of 0.2-0.45 m/s at the outlet .
- The requirement for a positive pressure differential in the operating room and surrounding areas in the range of 5-20 Pa.
New construction and renovation of hospital operating rooms to meet all the requirements of a Class 5 or higher cleanroom is quite expensive. The cost of just the enclosing structures of one operating room with “laminar” flow ranges from several tens of thousands of US dollars and more, plus the cost of a central air conditioning system. If air purity standards have been developed and implemented abroad, various rooms hospitals (in Germany and Holland combined the number of operating clean operating rooms is more than 800), then in our country the question of setting requirements for equipping the operating room with all systems is often decided at the level of the hospital’s chief physician and his deputies, who are sometimes simply unfamiliar with regulatory requirements to clean rooms, and their choice is determined primarily by financial capabilities, especially in budget organizations.
Having examined the complex general requirements to emergency ventilation and air conditioning systems, we can conclude that the correct organization of air flows (unidirectional, non-unidirectional) is one of the most important conditions ensuring the required air purity and patient safety. The air flow must remove all particles emitted by people, equipment and materials from the clean area.
In Fig. 1 presents the most common schemes for supplying air to the operating room and performed a comparative analysis of them in terms of bacterial contamination. Scheme 1d provides unidirectional vertical air flow, the other schemes provide non-unidirectional air flow.
The quality of the unidirectional air flow is greatly influenced by the design of the distributor, through which the air passes directly into the clean room. This distributor is located directly between the HEPA filters and the frequency converter. It can be made in the form of a lattice or in the form of a single or double mesh made of metal or synthetic material. The size of the hole and the distance between the holes through which air passes are important. The greater this distance, the worse the flow quality (Fig. 2).
If in rooms with unidirectional air flow the air distributor occupies the entire ceiling area above the operating area, then in rooms of a lower cleanliness class with non-unidirectional air flow, supply diffusers occupy only part of the ceiling, sometimes very small. Exhaust grilles can also be located in various ways(schemes 1a, 1b, 1c, 1d). In this case, only numerical mathematical modeling methods make it possible to take into account the variety of influencing factors on the pattern of air flows and evaluate how the position of filters, equipment, heat sources (lamps, etc.) affects air flows and the cleanliness class in various areas of the operating room.
Different kinds Designs of ceiling diffusers with a filter for clean rooms manufactured by GEA are shown in Fig. 3.
Such diffusers are equipped with sealed valves that allow the air filter to be isolated from the rest of the air conditioning system. This allows you to replace the air filter without turning off the air conditioner. The tightness of the air filter installation in the diffuser cell can be monitored using a tightness sensor. Sensors are also built in to measure the pressure drop across the filter.
Main results comparative analysis in various ways submissions clean air in operating rooms according to the work are presented in Fig. 4.
The figure shows the measurement results for various flows, as well as two limit curves that must not be exceeded for operating rooms of type A (particularly high requirements according to DIN 1946, part 4, edition 1998) or type B (high requirements).
Using the indicator of microbial contamination with a known volumetric air flow rate, it is possible to calculate microbial contamination (CFU/m3)*: K=n.Q.ms/V,
Where:
K - colony-forming units per 1 m 3 of air;
Q is the initial intensity of microbial sources;
ms is an indicator of microbial contamination;
V - volumetric air flow;
n is the number of personnel in the operating room.
The work draws the following conclusions. Separate diffusers or perforated ceilings provide clean air and mix it with polluted air (dilution method). Microbial contamination rates are at best around 0.5. With a unidirectional “laminar” air flow, a microbial contamination rate of 0.1 or less is achieved.
As mentioned above, with radial outlet diffusers on the ceiling, a mixed flow is created in the room. Such an output at a volume flow rate of 2,400 m 3 /h meets the standard requirements of class B, and a flow rate of 2,400 m 3 /h can be accepted as the minimum permissible flow rate of clean air supplied to the operating area (this flow rate is accepted as the reference volume flow rate in the standard DIN 4799, developed for the evaluation and comparison of different types of ceilings).
Today, ceiling-type mesh air distribution devices for creating unidirectional air flow for operating rooms are produced by a number of companies, for example, , ADMECO AG, ROX LUFTTECHIK GmbH, etc.
In Fig. Figure 5 shows a typical design diagram of such an air distribution device (laminar ceiling).
In practice, the most common size of such devices (ceilings) is from 1.8x2.4 m2 to 3.2x3.2 m2, and the latter size is the most common abroad. For example, for1.8x2.4 m 2 required consumption air will be 3100 m 3 / h (at a speed of air exit from the device of 0.2 m/s). From the practice of designing several operating rooms at the Moscow Central Institute of Traumatology and Orthopedics (CITO) by our design department, we can conclude that such a flow rate corresponds to a 25-fold exchange of air in a room with an area of 30-40 m2 and always exceeds the calculated flow rate necessary for the assimilation of excess heat characteristic for typical staffing and equipment for these premises.
Our data are in good agreement with the data of the work, which provides a heat release value of 1.5-2.0 kW, typical for operating rooms, as well as an estimated clean air supply of 2000-2500 m 3 / h (17-20 times per hour). In this case, the temperature of the supply air should differ from the temperature of the operating area by no more than 5 degrees.
How larger size laminar ceiling in the above range, the higher the degree of patient safety, but at the same time capital and operating costs increase significantly. A reasonable compromise is widely used abroad - the introduction of an air recirculation system in the operating room through highly efficient HEPA filters built into the “laminar” ceiling. This allows you to increase the size of the “laminar” ceiling to 3.2x3.2 m2 while maintaining low capital and operating costs for the central air conditioner.
For example, operating rooms are designed where, when outside air is supplied by an air conditioner at 1200-2000 m 3 /h, the circulation flow rate in the operating room is up to 8000 m 3 /h, while energy supply costs are significantly reduced. Increase in sizeup to 3.2x3.2 m2 allows you to include not only the patient in the sterile area, but also a table for instruments and working personnel, especially if you also use special enclosing plastic aprons (Fig. 6).
Another advantage of the system of using air circulation in the operating room (which is allowed in accordance with part 4 of the DIN 1946 standard) is the ability, at night, when the operating room equipment is not in use, to turn off the air conditioning to the supply of outside air completely or partially, using only the equipment (fan ) internal system circulation of clean air, while using approximately 400 W of power.
Speaking about energy saving in EQA systems for operating rooms in hospitals, we should note the work of Prof. O. Ya. Kokorina. This work also proposes the use of a circulating mixing and purifying supply unit, but this scheme was analyzed only for the option of supplying a non-uniform flow of clean air in the operating room according to the scheme presented in Fig. 1a.
Despite the energy attractiveness of the proposed scheme, when implementing it, designers may have problems with the need to place a mixing and cleaning unit with a capacity of 2,400 m3/h in rooms next to the operating room, as well as problems with the distribution of air supply and air ducts. exhaust systems, because a monoblock supply and exhaust unit is used.
* The term CFU means “colony forming units” (in English CFU - Colony Forming Units) and is a more accurate characteristic of microbial contamination. Clean room technology makes it possible to ensure a level of microbial contamination of less than 10 CFU/m 3 . There is evidence that reducing microbial air pollution in the operating table area reduces the risk of infection by 10 times by 2%.
Example:
Q=30,000 microbes per person per hour (assumption). For 8 people in the operating room with µs = 0.1 and a volume flow of 2400 m 3 /h K = 8x30000x0.1/2400 = 10 CFU/m3.
Published in ABOK magazine
In the spread of hospital infections highest value has an airborne droplet route, due to
than to constantly ensure the cleanliness of the air in the premises of a surgical hospital and operating unit
should be given great attention.
The main component that pollutes the air in a surgical hospital and operating unit is
is dust of the finest dispersion on which microorganisms are sorbed. Sources of dust
are mainly ordinary and special clothing for patients and staff, bedding,
the entry of soil dust with air currents, etc. Therefore, measures aimed at reducing
contamination of operating room air primarily involves reducing the influence of sources of contamination
to the air.
Persons with septic wounds or any purulent wounds are not allowed to work in the operating room.
Staff must shower before surgery. Although research has shown that in many cases shower
was ineffective. Therefore, many clinics began to practice taking a bath with a solution
antiseptic. At the exit from the sanitary checkpoint, the staff puts on a sterile shirt, pants and shoe covers. After
hand treatment in the preoperative room, wear a sterile gown, gauze bandage and sterile gloves.
The surgeon’s sterile clothing loses its properties after 3-4 hours and is sterilized. Therefore, when
In complex aseptic operations (such as transplantation), it is advisable to change clothes every 4 hours. These
The same requirements apply to the clothing of personnel serving post-transplant patients in the wards.
intensive care.
The gauze bandage is an insufficient barrier to pathogenic microflora, and, as shown
studies, about 25% of postoperative purulent complications are caused by a strain of microflora sown
both from the festering wound and from the oral cavity of the operating surgeon. Barrier functions of gauze
dressings improve after processing it Vaseline oil before sterilization.
Patients themselves may be a potential source of contamination, so they should be prepared before
operation accordingly.
Among the measures aimed at ensuring clean air, correct and
constant air exchange in hospital premises, practically eliminating the development of intra-hospital
infections. Along with artificial air exchange, it is necessary to create conditions for aeration and ventilation
premises of the surgical department. Particular preference should be given to aeration, which allows
for many hours and even around the clock in all seasons of the year natural air exchange,
which is a decisive link in the chain of measures to ensure clean air.
In-wall ventilation ducts contribute to increasing the efficiency of aeration. Effective
the functioning of these channels is especially necessary during winter and transition periods, when the air
premises are largely polluted by microorganisms, dust, carbon dioxide, etc. Research
show that the more air is removed through the exhaust ducts, the more relatively clean air there is in
Bacteriologically, outside air enters through transoms and various leaks. Due to
This requires systematically cleaning the ventilation ducts from dust, cobwebs and other debris.
Efficiency of in-wall ventilation ducts increases if at their upper end part
(on the roof) install deflectors.
Ventilation must be carried out during wet cleaning hospital premises (especially
in the morning) and the operating room after work.
In addition to the above measures to ensure air purity and destruction of microorganisms
Disinfection using ultraviolet radiation and, in some cases, chemicals is used. With this
purpose, the indoor air (in the absence of personnel) is irradiated bactericidal lamps type DB-15, DB-30 and
more powerful, which are placed taking into account convection air currents. Number of lamps
is set at the rate of 3 W per 1 m 3 of irradiated space. In order to mitigate the negative aspects
action of lamps, instead of direct irradiation of the air, diffuse radiation should be used, i.e.
produce irradiation in the upper zone of the premises with subsequent reflection of radiation from the ceiling, for which
you can use ceiling irradiators, or light luminescent lamps simultaneously with bactericidal ones
lamps.
To reduce the possibility of microflora spreading throughout the operating room
It is advisable to use light bactericidal curtains created in the form of radiation from lamps above the doors, in
open passages, etc. The lamps are mounted in metal spotlight tubes with a narrow slot (0.3-
0.5cm).
Air neutralization chemicals carried out in the absence of people. For this purpose
Propylene glycol or lactic acid may be used. Spray propylene glycol
at the rate of 1.0 g per 5 m 3 of air. Lactic acid used for food purposes is used at the rate of 10
mg per 1 m 3 of air.
Aseptic air quality in the premises of a surgical hospital and operating unit can also be achieved
the use of materials that have a bactericidal effect. These substances include derivatives
phenol and trichlorophenol, oxydiphenyl, chloramine, sodium salt of dichloroisocyanuric acid, naphthenylglycine,
cetyloctadecylpyridinium chloride, formaldehyde, copper, silver, tin and many others. They are impregnated
bed and underwear, dressing gowns, dressings. In all cases, the bactericidal properties of materials
lasts from several weeks to a year. Soft fabrics with bactericidal additives retain bactericidal
action for more than 20 days.
It is very effective to apply film or various varnishes and paints to the surface of walls and other objects,
to which bactericidal substances are added. For example, oxydiphenyl mixed with surface active
substances are successfully used to impart a residual bactericidal effect to the surface. Should
Keep in mind that bactericidal materials do not have a harmful effect on the human body.
In addition to bacterial pollution, air pollution in operating rooms is also of great importance.
narcotic gases: ether, fluorotane, etc. Research shows that during the operation in
the air in operating rooms contains 400-1200 mg/m 3 of ether, up to 200 mg/m 3 or more of fluorotane, and up to 0.2% carbon dioxide.
Very intense air pollution with chemicals is an active factor
contributing to the premature onset and development of fatigue among surgeons, as well as the emergence
unfavorable changes in their health.
In order to improve the air environment of operating rooms, in addition to organizing the necessary air exchange
drug gases entering the operating room airspace from
anesthesia machine and exhaled sick air. Activated carbon is used for this. Last
placed in a glass vessel connected to the valve of the anesthesia machine. The air exhaled by a sick person
Very often, a term called “clean rooms” is applied to operating rooms.
In all “clean rooms” it is necessary to strictly adhere to certain requirements for the frequency of air exchange, air humidity and cleanliness. In such rooms, humidity and air temperature values are very accurately observed. In the operating units of general surgery, which include labor, anesthesia and the operating room, it is supported temperature regime within 20 - 23 degrees Celsius, and the relative humidity should be 55 - 60%. These rules are followed due to several important reasons. When the relative air humidity is below 55%, the process of formation of static electricity begins in these rooms. In parallel with this, during the medical and technological course of operations, gases are formed that are used for anesthesia. When a critical level of static electricity is reached, these gases can explode. Also, at low relative humidity, unsatisfactory health of medical personnel is possible. Therefore, to prevent this, it is necessary to maintain indoor constant temperature. To create the most comfortable thermal conditions for doctors working in special clothing (bandages, suits, gowns, gloves) that impair heat transfer, the temperature should not exceed 23 degrees.
According to a number of microbiological studies, it has been revealed that as a result of human excretion of moisture, the rate of formation of bacteria in the human body significantly increases. According to established standards, air mobility in the area where the patient’s head is located should not exceed 0.1 - 0.15 m/sec. Due to the fact that postoperative wound infections are still quite common, all anti-epidemiological requirements with the use of antibiotics are observed in operating rooms, and strict requirements are imposed on climate control units.
Now there is a tendency to locate “clean rooms” away from the facades, in the central part of the building, where there are no heat exchange processes through the fence with outdoor environment. In order to compensate for excess heat in such rooms, a supply of fresh air volume up to 2500 cubic meters per hour (up to 20 times per hour at standard sizes operating room). An important fact is that the supply air temperature can exceed the room temperature by only 5 degrees. According to microbiological research, this amount of fresh air will be quite enough to dilute and remove the bacterial flora.
Since the air supplied to the operating rooms must be absolutely sterile, attention is paid to its purification special meaning. Filters are a very important component of the climate system in clean rooms. It is with their help that the required degree of air purity is achieved in the room. Thanks to filters with different degrees of purification (coarse, fine in the first and second stages), the air undergoes three-stage purification. At the third stage, thanks to the use of microfilters and filters, the incoming air reaches the required level of fine purification. To extend the service life of the main filters, install filters with a lower degree of purification, performed in the form of a preliminary cycle.
The widest range of high-quality air purifiers, developed and produced in Russia, which are so indispensable for creating necessary conditions in operating rooms, presented in
Description:
Operating rooms are one of the most critical links in the structure of a hospital building in terms of the importance of the surgical process, as well as providing the special microclimate conditions necessary for its successful implementation and completion. Here, the source of the release of bacterial particles is mainly medical personnel, who are able to generate particles and release microorganisms when moving around the room.
Hospital operating rooms
Air flow control
Over the past decades, in our country and abroad, there has been an increase in purulent-inflammatory diseases caused by infections, which, according to the definition of the World Health Organization (WHO), are commonly called nosocomial infections (HAIs). An analysis of diseases caused by nosocomial infections shows that their frequency and duration are directly dependent on the state of the air environment in hospital premises. To ensure the required microclimate parameters in operating rooms (and industrial clean rooms), unidirectional flow air distributors are used. The results of monitoring the air environment and analyzing the movement of air flows showed that the operation of such distributors provides the required microclimate parameters, but often worsens the bacteriological purity of the air. To protect the critical area, it is necessary that the air flow leaving the device maintains straightness and does not lose the shape of its boundaries, that is, the flow should not expand or contract over the protected area where the surgical
Operating rooms are one of the most critical links in the structure of a hospital building in terms of the importance of the surgical process, as well as providing the special microclimate conditions necessary for its successful implementation and completion. Here, the source of the release of bacterial particles is mainly medical personnel, who are able to generate particles and release microorganisms when moving around the room. The intensity of particles entering indoor air depends on the degree of mobility of people, temperature and air speed in the room. Nosocomial infections tend to move around the operating room with air currents, and there is always a risk of its penetration into the unprotected wound cavity of the patient being operated on. From observations it is obvious that improperly organized operation of ventilation systems leads to intensive accumulation of infection to levels exceeding permissible levels.
For several decades, specialists from different countries have been developing system solutions to ensure operating room air conditions. The air flow supplied to the room must not only assimilate various harmful substances (heat, humidity, odors, harmful substances) and maintain the required microclimate parameters, but also ensure the protection of strictly established areas from infections entering them, that is, the necessary cleanliness of indoor air. The area where invasive interventions are carried out (penetration into the human body) can be called the operating zone or “critical”. The standard defines such an area as an “operating sanitary protection zone” and means by it the space where the operating table, auxiliary tables for instruments and materials, equipment, as well as medical personnel in sterile clothing are located. There is the concept of a “technological core”, which refers to the area where production processes are carried out under sterile conditions, which in meaning can be correlated with the operating area.
To prevent the penetration of bacterial contaminants into the most critical areas, screening methods have become widely used through the use of displacement air flow. Laminar air flow air distributors were created various designs, the term "laminar" was subsequently changed to "unidirectional" flow. Currently, you can find a variety of names for air distribution devices in clean rooms, such as “laminar”, “laminar ceiling”, “operating ceiling”, “ operating system clean air”, etc., which does not change their essence. The air distributor is built into the ceiling structure above the protection zone of the room and can be of different sizes depending on the air flow. Recommended optimal area such a ceiling must be at least 9 m2 in order to completely cover the operating area with tables, equipment and personnel. The displacing air flow at low speeds comes from top to bottom, like a curtain, cutting off both the aseptic field of the surgical intervention zone and the zone of transfer of sterile material from environment. Air is removed from the lower and upper zones of the room simultaneously. HEPA filters (class H according to) are built into the ceiling structure, through which the supply air passes. Filters trap but do not disinfect living particles.
Currently, much attention is being paid all over the world to the issues of air disinfection in hospitals and other institutions where there are sources of bacterial contamination. The documents voiced requirements for the need to disinfect operating room air with a particle inactivation efficiency of at least 95%, as well as air ducts and climate system equipment. Bacterial particles released by surgical personnel continuously enter the room air and accumulate in it. To ensure that the concentration of particles in indoor air does not reach maximum permissible levels, air control is necessary. Such monitoring must be carried out after installation of climate control systems, maintenance or repair, that is, in the operating mode of a clean room.
The use of unidirectional flow air distributors with built-in ceiling-type ultra-fine filters in operating rooms has become common among designers. Air flows of large volumes go down the room at low speeds, cutting off the protected area from the environment. However, many professionals are unaware that these solutions are not sufficient to maintain adequate levels of air disinfection during surgical procedures.
The fact is that there are quite a lot of designs of air distribution devices, each of which has its own area of application. Operating room cleanrooms within their “clean” class are divided into classes according to the degree of cleanliness, depending on their purpose. For example, general surgical operating rooms, cardiac surgery or orthopedic operating rooms, etc. Each specific case has its own requirements for ensuring cleanliness.
The first examples of the use of air distributors for clean rooms appeared in the mid-1950s. Since then, it has become traditional to distribute air in clean production rooms through a perforated ceiling when low concentrations of particles or microorganisms are required. The air flow moves through the entire volume of the room in one direction at a uniform speed, usually 0.3–0.5 m/s. The air is supplied through a bank of high-efficiency air filters located on the ceiling of the cleanroom. The air supply is organized on the principle of an air piston moving downward through the entire room, removing contaminants. Air is removed through the floor. This type of air movement contributes to the removal of aerosol contaminants, the sources of which are personnel and processes. This arrangement of ventilation is aimed at ensuring clean air in the room, but requires large air flows and is therefore uneconomical. For cleanrooms of class 1000 or ISO class 6 (ISO classification), the air exchange rate can range from 70 to 160 times per hour.
Subsequently, more rational modular devices of much smaller sizes with low costs appeared, making it possible to select an air supply device based on the size of the protected area and the required air exchange rates of the room, depending on the purpose of the room.
Analysis of the operation of laminar air distributors
Laminar flow units are used in clean production rooms and serve to distribute large volumes of air, providing for specially designed ceilings, floor hoods and room pressure regulation. Under these conditions, the operation of laminar flow distributors is guaranteed to provide the required unidirectional flow with parallel flow lines. A high air exchange rate helps maintain conditions close to isothermal in the supply air flow. Ceilings designed for air distribution with large air exchanges, due to their large area, provide a low initial air flow velocity. The operation of exhaust devices located at floor level and control of air pressure in the room minimize the size of recirculation flow zones, and the principle of “one pass and one exit” is easily implemented. Suspended particles are pressed against the floor and removed, so there is little risk of them being recirculated.
However, when such air distributors operate in an operating room, the situation changes significantly. To maintain acceptable levels of bacteriological purity of air in operating rooms, calculated air exchange values usually average 25 times per hour or even less, that is, they are not comparable with the values for production premises. To maintain stable air flow between the operating room and adjacent rooms, excess pressure is usually maintained in it. Air is removed through exhaust devices symmetrically installed in the walls of the lower zone of the room. To distribute smaller volumes of air, laminar flow devices are usually used small area, which are installed only above the critical area of the room in the form of an island in the middle of the room, instead of using the entire ceiling.
Observations show that such laminar devices will not always provide unidirectional flow. Since there is almost always a difference between the temperature in the supply stream and the ambient air temperature (5-7 ° C), the cooler air leaving the supply device descends much faster than an isothermal unidirectional flow. This is a common occurrence for ceiling diffusers used in public buildings. There is a misconception that laminar floors provide stable, unidirectional airflow regardless of location or method of application. In fact, in real conditions the speed of the low temperature vertical laminar flow will increase as it approaches the floor. The larger the volume of supply air and the lower its temperature relative to the room air, the greater the acceleration of its flow. The table shows that the use of a laminar system with an area of 3 m 2 with a temperature difference of 9 ° C gives a threefold increase in air speed already at a distance of 1.8 m from the beginning of the path. The air speed at the outlet of the supply device is 0.15 m/s, and at the level of the operating table it reaches 0.46 m/s. This value exceeds permissible level. It has long been proven by many studies that with excessive inflow flow rates it is impossible to maintain its “unidirectionality”. Analysis of air control in operating rooms, carried out, in particular, by Salvati (1982) and Lewis (Lewis, 1993), showed that in some cases the use of laminar flow units with high air velocities leads to an increase in the level of air contamination in the area of the surgical incision with subsequent risk of infection.
| Dependence of air flow speed on area laminar panel and supply air temperature |
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T - difference between the temperature of the supply and ambient air |
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When the flow moves, at the initial point the air flow lines will be parallel, then the boundaries of the flow will change, narrowing towards the floor, and it will no longer be able to protect the area determined by the dimensions of the laminar flow unit. At air speeds of 0.46 m/s, the flow will capture low-moving air from the room. Since bacterial particles are constantly released in the room, infected particles will be mixed into the air flow coming from the supply unit, since the sources of their release are constantly operating in the room. This is facilitated by air recirculation resulting from pressurized air in the room. To maintain the cleanliness of operating rooms, according to the standards, it is necessary to ensure an imbalance of air due to the excess of the inflow over the exhaust by 10%. Excess air moves to adjacent less clean rooms. In modern conditions, hermetic sliding doors are often used in operating rooms; excess air has nowhere to go; it circulates throughout the room and is taken back into the supply unit using fans built into it for further cleaning in filters and secondary supply to the room. The circulating air collects all contaminated particles from the air in the room and, moving near the supply flow, can pollute it. Due to the violation of the boundaries of the flow, air from the surrounding space is mixed into it and pathogenic particles penetrate into the sterile zone, which is considered protected.
High mobility promotes intensive detachment of dead skin particles from unprotected areas of the skin of medical personnel and their entry directly into the surgical incision. On the other hand, it should be noted that the development of infectious diseases in the postoperative period is caused by the hypothermic state of the patient, which intensifies when exposed to flows of cold air of increased mobility.
Thus, a laminar flow air diffuser, traditionally used and effective in a cleanroom environment, may be detrimental to operations in a conventional operating room.
This conversation is valid for laminar flow devices, which have an average area of about 3 m 2 - optimal for protecting the operating area. According to American requirements, the air flow velocity at the outlet of laminar panels should not exceed 0.15 m/s, that is, 14 l/s of air should flow into the room from 1 ft 2 (0.09 m 2) of panel area. In our case, this will be 466 l / s (1677.6 m 3 / h) or approximately 17 times / h. According to the standard value of air exchange in operating rooms, it should be 20 times per hour, 25 times per hour, so 17 times per hour fully meets the requirements. It turns out that the value of 20 times per hour corresponds to a room with a volume of 64 m 3.
According to today's standards, the area of a standard operating room (general surgery) should be at least 36 m2. And the requirements for operating rooms for more complex operations (cardiological, orthopedic, etc.) are much higher, and often the volume of such an operating room can exceed 135–150 m 3 . The air distribution system for these cases will require a significantly larger area and air capacity.
In the case of organizing air flow in larger operating rooms, the problem arises of maintaining laminarity of flow from the exit plane to the level of the operating table. Air flow behavior studies have been conducted in several operating rooms. Laminar flow panels were installed in different rooms, which were divided by area into two groups: 1.5–3 m 2 and more than 3 m 3, and experimental air conditioning units were installed that made it possible to change the temperature of the supply air. Repeated measurements of the flow rate of incoming air were carried out at various flow rates and temperature changes, the results of which can be seen in the table.
Criteria for room cleanliness
Correct decisions regarding the organization of air distribution in operating rooms: choosing the rational size of supply panels, ensuring the standard flow rate and temperature of supply air - do not guarantee absolute disinfection of the air in the room. The issue of air disinfection in operating rooms was acutely raised more than 30 years ago, when various anti-epidemiological measures were proposed. And now the goal of the requirements of modern regulatory documents for the design and operation of hospitals is air disinfection, where HVAC systems are presented as the main way to prevent the spread and accumulation of infections.
For example, the standard considers disinfection to be the main goal of its requirements, noting: “a properly designed HVAC system minimizes the airborne transmission of viruses, bacteria, fungal spores and other biological contaminants,” and HVAC systems play a major role in controlling infections and other harmful factors. The requirement for operating room air conditioning systems is highlighted: “the air supply system must be designed to minimize the introduction of bacteria into sterile areas along with the air, while also maintaining the maximum level of cleanliness in the rest of the operating room.”
However, regulatory documents do not contain direct requirements for determining and monitoring the effectiveness of disinfection for various ventilation methods, and designers often have to engage in search activities, which takes a lot of time and distracts from the main work.
In our country there is quite a lot of different regulatory literature on the design of HVAC systems for hospital buildings, and requirements for air disinfection are voiced everywhere, which, for many objective reasons, are practically difficult for designers to implement. This requires not only knowledge of modern disinfection equipment and the correct use of it, but, most importantly, further timely epidemiological monitoring of the indoor air environment, which gives an idea of the quality of operation of HVAC systems, but, unfortunately, is not always carried out. If the cleanliness of clean industrial premises is assessed by the presence of particles (for example, dust particles), then the indicator of air cleanliness in clean rooms of medical buildings is live bacterial or colony-forming particles, the permissible levels of which are given in. To maintain these levels, the air environment should be regularly monitored for microbiological indicators, for which it is necessary to be able to count them. The methodology for collecting and counting microorganisms to assess air purity has not yet been presented in any of the regulatory documents. It is important that the counting of microbial particles should be carried out in the operating room, that is, during the operation. But for this, the design and installation of the air distribution system must be ready. The level of disinfection or the efficiency of the system cannot be determined before it starts operating in the operating room; this can only be done under conditions of at least several operating processes. This poses great difficulties for engineers, since research, although necessary, is contrary to the hospital’s anti-epidemic discipline.
Air curtain
To ensure the required air conditions in the operating room, it is important to properly organize the joint work of air inflow and removal. By rationally positioning supply and exhaust devices in the operating room, the nature of air flow can be improved.
In operating rooms, it is impossible to use both the entire ceiling area for air distribution and the floor area for air removal. Floor hoods are unhygienic because they get dirty quickly and are difficult to clean. Bulky, complex and expensive systems have never found their application in small operating rooms. For these reasons, the most rational is the “island” arrangement of laminar panels above the critical area with the installation of exhaust openings in the lower part of the walls. This makes it possible to simulate air flows similar to an industrial clean room in a cheaper and less cumbersome way. A method that has proven successful is the use of air curtains operating on the principle of a protective barrier. The air curtain combines well with the flow of supply air in the form of a narrow “shell” of air at a higher speed, specially organized around the perimeter of the ceiling. The air curtain continuously works for exhaust and prevents the entry of contaminated ambient air into the laminar flow.
To understand the operation of an air curtain, you should imagine an operating room with an exhaust hood arranged on all four sides of the room. The supply air coming from the “laminar island” located in the center of the ceiling will only fall down, expanding towards the sides of the walls as it descends. This solution reduces recirculation zones, the size of stagnant areas in which pathogenic microorganisms collect, and also prevents mixing of the laminar flow with the room air, reduces its acceleration and stabilizes the speed, as a result of which the downward flow covers (locks) the entire sterile area. This helps remove biological contaminants from the protected area and isolate it from the environment.
In Fig. Figure 1 shows a standard air curtain design with slots around the perimeter of the room. When organizing exhaust along the perimeter of the laminar flow, it stretches, it expands and fills the entire zone inside the curtain, as a result of which the “narrowing” effect is prevented and the required speed of the laminar flow is stabilized.
From Fig. Figure 3 shows the values of the actual (measured) speed that occurs with a properly designed air curtain, which clearly demonstrate the interaction of the laminar flow with the air curtain, and the laminar flow moves uniformly. The air curtain eliminates the need to install a bulky exhaust system around the entire perimeter of the room, instead of installing a traditional hood in the walls, as is customary in operating rooms. The air curtain protects the area directly around the surgical personnel and table, preventing contaminated particles from returning to the primary air stream.
After designing an air curtain, the question arises as to what level of disinfection can be achieved during its operation. A poorly designed air curtain will be no more effective than a traditional laminar flow system. A design mistake may be high air speed, since such a curtain will “pull” the laminar flow too quickly, that is, even before it reaches the operating floor. Flow behavior may not be controlled and there may be a risk of contaminated particles leaking into the operating area from floor level. Likewise, an air curtain with a low suction speed cannot effectively block laminar flow and may be drawn into it. In this case, the air condition of the room will be the same as when using only a laminar air supply device. When designing, it is important to correctly determine the speed range and select the appropriate system. This directly affects the calculation of disinfection characteristics.
Despite the obvious advantages of air curtains, they should not be used blindly. The sterile airflow created by air curtains during surgery is not always required. The need to ensure the level of air disinfection should be decided together with technologists, whose role in this case should be surgeons involved in specific operations.
Conclusion
Vertical laminar flow can behave unpredictably depending on its operating conditions. Laminar flow panels used in clean production areas generally cannot provide the required level of disinfection in operating rooms. Air curtain systems help correct the movement pattern of vertical laminar flows. Air curtains are the optimal solution to the problem of bacteriological control of the air environment in operating rooms, especially during long surgical operations and patients with a compromised immune system, for whom airborne infections pose a particular risk.
The article was prepared by A. P. Borisoglebskaya using materials from the ASHRAE journal.
“Clean” rooms are intended for patients who need isolation from an unfavorable environment, with weakened immunity, when treating large wound surfaces, during medical procedures that require compliance with special air cleanliness indicators, i.e. the countable concentration of aerosol particles and the number of microorganisms in the air are maintained within certain limits.
Such premises can be equipped with: operating rooms, pre- and postoperative wards, burn departments, intensive care wards, boxes for infectious patients, microbiological, virological or other medical laboratories, pharmaceutical production premises and many other medical premises.
Currently, cleanliness technology in medical institutions has become an integral part of civilized healthcare and is the key to the success of the entire treatment process.
Cleanroom technology
Product quality and applicable standards for microelectronics, optics and pharmaceutical production depend on the purity class prevailing in each industry.
Suspended floors are often used. The empty space under the floor can be used to provide air circulation and accommodate pipes and cables, depending on the design of the room.
Optimal production conditions can only be created using high-precision technology. This technology includes efficient air conditioning and filtration.
However, one of the main factors determining the effectiveness of a cleanroom is the quality of the ceiling, walls, and floors from which the room is constructed. Depending on the cleanliness class, a clean ceiling using filters for laminar flow is used (cleanliness class = 10000).
Walls must separate the cleanroom area from other production and office premises (external adjacent walls), and at the same time separate rooms with different cleanliness classes. Different air cleanliness requirements include different operating parameters.
Interior partition walls must be easily adaptable to changing production requirements (semiconductor manufacturing cycles change every 3-4 years) in a cleanroom environment.
From the very beginning, cleanroom technology has developed in the USA along with computer technology. Since then, cleanrooms have been divided into cleanliness classes. Thus, English terminology is used in cleanroom technology.
Clean room classes.
| Class | Particle size (measured in 28L of air with a micrometer) | ||||
|---|---|---|---|---|---|
| 0.1 | 0.2 | 0.3 | 0.5 | 5.0 | |
| 1 | 35 | 7.5 | 3 | 1 | NP |
| 10 | 350 | 75 | 30 | 10 | NP |
| 100 | NP | 750 | 300 | 100 | NP |
| 1000 | NP | NP | NP | 1000 | 7 |
| 10000 | NP | NP | NP | 10000 | 70 |
| 100000 | NP | NP | NP | 100000 | 700 |
(NP - not applicable)
According to US Federal Standard 209 d
According to VDI 2083
The US Federal Standard is today the basis for defining technical requirements. VDI guidance is used less frequently.