1、N A-04-7-4 Controlled Clean Operating Room Area J. Shen, Ph.D. Member ASHRAE ABSTRACT New China standards, the “Construction Standard for Clean Operating Room in Hospital” and the “Architectural Code for Clean Operating Room in Hospital” have been published. These standards make a breakthrough in th
2、e technical approaches for industrial cleanrooms and emphasize that a clean operating department serves as a biocleanroom and a controlled environment. This paper introduces the general principles and recommended practice that the new standards require. INTRODUCTION With the medical development in C
3、hina, the level of medical technology has been greatly raised and medical requirements have been largely changed. Thus, the require- ments for hospitals to be constructed and extended has become all the more severe. Surgical technology is increasingly deli- cate. According to the statistics, by the
4、end of 1998, China had 16,468 hospitals, including 1,527 county-level or above county-level hospitals, 7,498 hospitals with over 100 beds, 788 hospitals with over 500 beds. However, there are only over a hundred hospitals with converted clean operating depart- ments to date, which account for 1.25%
5、of the total number of hospitals. Therefore, some medical units strive for conversion into clean operating departments. The construction of a clean operating department has been a priority for many hospitals. The operating departments become a key link for infection control in hospitals. In the past
6、, China did not understand clean operating rooms very well. The design of operating rooms in our country is influenced greatly by cleanroom industry techniques. This only emphasizes the cleanlincss level, the air change rates, or the widespread usage of unidirectional flow, and so on, but ignores th
7、e establishment of the systemic and synthetic safe- guard. This is the main cause of the high construction and operating cost of clean operating rooms, while the potential for contamination problems is not effectively resolved in our country. Nevertheless, there have been no construction stan- dards
8、 and codes for clean hospital operating rooms in China. Although, the “Construction Technical Norm of Military Hospital Clean Operating Room Area” was enacted in 1995, the hospitals in most places did not have to follow. “Standards for Construction of Hospital Clean Operation Room” (referred to as “
9、Standard” herein) was published in October 2000, and “the Architectural Technical Code for Hospital Clean Operating Room” (referred to as “Code” herein) was published in December 2002. This could be a landmark in China because it means that the design of hospital clean air-conditioning in China has
10、stepped away from use of cleanroom industry techniques, and some new ideology and principles were employed to construct operating rooms in an economical and effective way. THE GUIDING IDEOLOGY AND BASIC PRINCIPLE IN WORKING OUT THE STANDARD A lot of thought went into controlling clean operating room
11、 areas as the practice was developed. It was understood that not only the does the clean air conditioning system play an important role in controlling the environment in the operating room, but it also must maintain control throughout the oper- ating process. The goal of the system should be to main
12、tain a high indoor sterility level. In other words, the clean operating room should always be controlled in any case so as to lower any potential risk of infection. Jinming Shen is a professor at the HVAC Institute, Tongji University, Shanghai, China. 776 02004 ASHRAE. BIOCLEANROOM CHARACTERISTICS A
13、ND PROTECTION OF KEY AREAS The clean operating room is classified as a biological cleanroom, with the intention of controlling living particles. Therefore, the concentration of microbials should be used for the classification. Cleanroom systems could also be flexible in terms of air purifying treatm
14、ent, so people would be more wary of comprehensive measures taken for complete and all- encompassing control, and they would not view air purifying as an unity measure. Meanwhile, it could be said that clean operating room areas differ from common operating rooms only by the need to maintain sterili
15、zation. Without measures to purifi the air, the space would not be called a clean operating room. Hence, the essence of the clean operating room area is clearly defined. The Standard defined four grades for operating room areas. It employed the concept of protecting key areas and defined the central
16、 space and neighboring space in these clean operating room areas. Take Grade 2 Clean operating room area as a standard, Grade 1 is a more stringent requirement and is called a “Super” clean operating room, and Grade 3 is less stringent, and is called a “Common” clean operating room. To let ordinary
17、hospitals all use a clean operating room, Grade 4 is given, which is significant for the popularization of the clean operating room. The Standard states that a ceiling supply should be used in Grade 1, Grade 2, and Grade 3 operating rooms and the size of the ceiling supply should be appropriate to i
18、ts grade. Both the area and velocity of supply air could be decreased compared with prior practices. The scheme of local ventilation and operating room protection is more systematic. It is beneficial to the control of biocontamination and easy to operate. The Special Demand for Air Conditioning Comp
19、ared to air-conditioning systems for general build- ings, the system used in clean operating room areas satisfies the requirements for operations, which provides for control of infections while operating on wounds during surgical proce- dures and thus improves the success rate of operations. Therefo
20、re this type of system should have the following characteristics. I. Indoor environment control requirements 1. 2. 3. 4. 5. Maintain sterilization through indoor air cleaning in the operating room area. Control airflow pattern and air velocity. Maintain desired airflow direction and pressure distrib
21、ution between different areas. Ensure special required temperature and humidity for medical procedure. Exhaust pollutants such as noxious gas to ensure indoor air quality and exclude the external environ- ment (for any infective operating). 2. System design The type of clean air-conditioning system
22、in an operat- ing room could play a very important roll in maintaining different concentrations of airborne microbial contamination in different rooms. Several different methods were adopted to prevent cross-infection. The Standard regulates clean air- conditioning systems for clean operating rooms
23、and requires that systems with unique characteristics be installed for subsidiary rooms. An independent clean air-handling unit should be installed in each clean operating room area for Grade 1 and Grade 2; however, two or three clean operation rooms of Grade 3 or Grade 4 can share the same system,
24、and a centralized fresh air (or makeup) supply system could be adopted. 3. Positive tressure control The control of positive pressure is a more important aspect in a clean operating room area to attempt to guarantee system performance. Pressure control in order to keep the operating room area steril
25、e depends upon the airtightness of the space envelope. Contamination is prevented when the pressure in the sterile area is higher than the external area. Because the control concept in the clean operating room is based upon maintaining separate sterile areas instead of a single clean operating room,
26、 the different levels of spaces within a department needed distinct control of differential pressure. The ordered gradient pressure can ensure the direc- tional flow of clean air so that the air can only flow from the sterile spaces of a higher level to a lower level, including from the sterile area
27、s to the areas ofnonsterility. With the assurance that the ordered pressure gradient distribution in the clean operating room area could be maintained in any situation, the risks of infection in the operating area can indeed be reduced effectively. 4. Clean operating mom turndown The clean air-condi
28、tioning system was expected to be turned on or off promptly, if required, because continuous usage is infrequent. The Standard simply states that a whole operating room area should be always under control regardless whenever one system is on or off. It is not permitted that the whole operating room
29、area could be influenced by shutting down a portion of it. 5. Prevent secondary contamination in the system Biocontamination control in an air-conditioning system should receive higher attention. A clean operating room area using a traditional ventilation and air-conditioning system is not in confor
30、mance with the Standard because it might bring in dust, virus, and moisture to any area in the system, where microbial growth, particularly in the coil, filter, condensation pan, etc., could occur. Accumulated dust and moisture was called “primary contamination, and microbial growth was generally ca
31、lled “secondary contamination. So a traditional air-conditioning system could be a hotbed for microbial ASHRAE Transactions: Symposia 777 I Figure I A new type of clean air conditioning. contamination because it cannot keep the potential sources of biocontamination out of its system. A New Type of C
32、lean Air-Conditioning System As stated before, it was a baffling problem that the entire operating room area should always be under control in line with the ventilation regulation in the Standard. When a traditional air-conditioning system was employed in a clean operating room area, the desired air
33、flow directions in the whole area, along with positive pressures in different rooms, could not always be maintained. If one air-handling unit would stop, the distribution of positive differential pressure in the area could change. Then the indoor operating room environment would be polluted and cros
34、s-infection could occur as a result. It was not reasonable to only depend on an automatic system in the past. Therefore, a primary task is to cautiously choose the design of a clean operating room air- conditioning system. A new type of system has now been developed (shown in Figure 1) in China, whi
35、ch could keep the whole operating department always under control regardless of whether a clean air-handling unit is on or off. In the new type of system for clean operating room areas, there are individual air-handling units (AHU) and an indepen- dent unit supplying makeup air (MUAH). The AHU contr
36、ols each area to achieve the temperature, humidity, and the degree of clean air in these separate areas. Every operating room has its own exhaust air unit. Constant air volume devices (CAV) with two positions were adopted in each branch duct. In the first-position, a larger fresh airflow rate was su
37、pplied during normal operating conditions, and in the second-position, a lower fresh air flow rate was supplied only to maintain positive pressure. A reasonable method of preventing “secondary contam- ination” is to remove the sources of biocontamination, espe- cially particulates and moisture. Acco
38、rding to the requirements of the Standard, three-stage filtration should be set up in the independent fresh air unit, and the terminal filter must be greater than an F-10 filter. This requirement is based on removing most of the particles in the fresh air supply. The MUAH could be designed to remove
39、 all (or most) of the latent cooling load. It is possible for this system to eliminate “secondary contamination” in every AHU after it. 1. Control concept Figure 1 illustrates the following. This system is called a semi-central air system and con- sists of an independent fresh air-handling unit with
40、 an individual AHU for every clean operating room. The branches of the fresh air system, on which the CAV devices with two-position control are mounted, are directly connected to the supply air ducts for the individ- ual units on which a one-way damper is mounted to pre- vent makeup air from returni
41、ng. With the use of CAV devices having two-position con- trol, the independent fresh air-handling unit provides both the air volume to maintain positive pressure in each clean operating room and the normal fresh air. Then the individual AHU for each operating room tunis into a recirculating unit. Th
42、e indoor contaminants and odors are removed by their own exhaust unit. When an operating room is normally in use, the CAV device is adjusted to the first position, allowing a larger volume of fresh air to enter the room. The exhaust air volume is the difference in volume between the fresh air and th
43、e pressurization losses. When this operating room is unused, the CAV device with two-position control on the branch of the fresh air unit was adjusted to the lower level, allowing a relatively small volume of fresh air (or positive pressure air) to enter the room. With the exhaust 778 ASHRAE Transac
44、tions: Symposia unit shut down, the fresh air, forming positive pressure, can exfiltrate outdoors. All the air creating positive pres- sure in the area is supplied by the same unit, and thus the gradient pressure distribution in the whole clean operat- ing room area can be assured. So the rational p
45、ressure distribution and directional airflow in the clean operat- ing room area is able to achieve the desired results. The indoor exhaust unit is interlocked with an automatic door in the operating room and a time-delay device is installed. The moment when the door is opened, the exhaust unit shuts
46、 down immediately. When the door is closed, the exhaust unit starts up with a time delay, which ensures maintaining positive pressure when the door is open and also avoids frequent startup and shut- down of the exhaust unit due to the opening and closing of the door. Because most of the particles in
47、 the makeup air were already removed by the MUHU, the terminal HEPA fil- ter will not receive much particulate loading. The filter dust-hoid and the recirculating airflow rate can be changed slowly, and they could not affect the positive pressure control in this case. Practical automatic system Base
48、d on the above reasoning, a practical automatic system is described as below: When an operating room is in use, the open signal will inform its AHU and the exhaust unit to start up. At the same time, the CAV device with one-position control is required to operate at the high level. When an operating
49、 room is left unused, the “close” sig- nal will inform its AHU and the exhaust unit to shut down. At the same time, the CAV device with two-posi- tion control is required to operate at the low level. For control of the independent makeup air unit, a dipolar electrical motor can be used to adjust the air volume of the fan for the case when part of the operating rooms are in run mode. In the situation where more operating rooms (for example, more than 10 rooms) lead to more variation in fresh air volume conditions, the fresh air can be controlled with a frequency converter by use of con- sta
