Comparative analysis of technical requirements for Heating, Ventilating, and Air Conditioning (HVAC) systems in high-biocontainment facility standards

Highlights

• •We have sorted out the standards, specifications, and guidelines relevant to high-biocontainment facilities in China and some other countries, compared and analyzed the relevant requirements of each standard.
• •We have discussed the technical points and requirements for the Heating, Ventilating, and Air Conditioning (HVAC) systems in different standards.
• •Although the specific provisions of China and international biosafety standard systems are different due to different national conditions and cultural differences, the essence is determined based on the concept and logic of risk assessment, which is of mutual referential significance.

Abstract

In this study, standards of high-biocontainment facilities (including laboratories and large-scale production facilities) formulated by China and other countries were analyzed and compared, and the technical points and requirements for Heating, Ventilating, and Air Conditioning (HVAC) systems in different series of standards were discussed. The main focus was on expounding the design and verification of the containment area’s indoor parameters, ventilation system, filter design, integrity test, fan standby, airflow pattern, and system reliability. This study expects suggestions and opinions on the construction and development of biosafety facilities in China and the possible future revision of relevant national standards.

1. Introduction

With the outbreak and spread of the coronavirus disease 2019 (COVID-19) pandemic, biosafety has become a significant threat to the survival and development of humanity. Biosafety is an essential part of the overall national security, so biosafety risks have posed severe challenges to national security development and overall social stability. China has gradually established a relatively complete biosafety system and built a number of high-biocontainment facilities (including laboratories and large-scale production facilities) after nearly 20 years of development which provided conditions for scientific research, production, and services in the fields of population and animal health, making significant contributions to the life safety of the people and the prevention and control of major infectious diseases across China.

For high-biocontainment facilities, the Heating, Ventilating, and Air Conditioning (from now on referred to as HVAC) systems constitute a core component and a fundamental guarantee of their protective barrier. As the premise of safe and reliable operation of these facilities, the HVAC systems are essential for the safety of pathogenic micro-organic experimental and production activities, as well as the control of indoor environmental parameters and pressure. The standards and specifications in China and other countries stipulated for the HVAC systems of high-biocontainment facilities can be a reference since they are all essentially based on the concept and logic of risk assessment, regardless of differences in specific requirements due to various national and cultural conditions. Based on the design, testing, and standard compilation experiences of the author’s team, this study sorts out the standards, specifications, and guidelines relevant to high-biocontainment facilities (including laboratories and large-scale production facilities) in China and some other countries. Furthermore, it compares and analyzes the relevant requirements of each standard, expecting to provide suggestions on the construction and development of biosafety facilities in China and the future revision of relevant national standards.

2. Overview of requirements for HVAC systems in standards, specifications, and guidelines

2.1. Introduction to the requirements for HVAC systems in China’s standards, specifications, and guidelines

After years of exploration and development, China’s high-biosafety laboratory system has begun to take shape, and a series of relatively independent and complete standards have been gradually formed for laboratory biosafety construction. At present, the national standards mainly used for the construction of high-biosafety laboratories in China are GB 50346 Architectural and Technical Code for Biosafety Laboratories (from now on referred to as GB 50346), GB 19489 Laboratory—General Requirements for Biosafety (from now on referred to as GB 19489), GB 27421 Mobile Laboratories—General Requirements for Biosafety (from now on referred to as GB 27421), etc. Based on the same understanding of the construction index, these standards, complementary to each other, make relevant requirements for the HVAC systems [1], [2], [3]. The industry standards RB/T 199 Technical Code for Evaluating Biosafety Performance of Laboratory Equipment (from now on referred to as RB/T 199), JG/T 497 Exhaust High Efficiency Filtration Units and YY 0569 Class II Biological Safety Cabinets, etc., specify the technical requirements, evaluation methods and criteria of critical biosafety protective equipment associated with an HVAC system, such as biosafety cabinets (BSCs), isolator, individually ventilated cages (IVCs), exhaust high-efficiency filtration units, breathing air system, chemical shower cubicles and pass-through chambers [4], [5], [6]. The Guideline on Evaluation for Operation and Maintenance of Biosafety Laboratories, an industry standard of certification and accreditation under approval, stipulates the operation and maintenance requirements and evaluation for HVAC systems in high-biocontainment laboratories and related key protective equipment of biosafety. On April 15, 2021, the Biosafety Law of the People’s Republic of China (from now on referred to as Biosafety Law) was implemented, further enhancing the standardization, normalization, and legalization of biosafety in China [7].

Notably, in August 2017, the Ministry of Agriculture and Rural Affairs of China issued the Standard of Biocontainment Level-3 for Veterinary Vaccine Manufacturers (Announcement No. 2573 of the Ministry of Agriculture and Rural Affairs, from now on referred to as Level-3 Biocontainment Standard), stipulating the “Level-3 Protection” requirements for highly pathogenic veterinary vaccine (typically full-virus foot-and-mouth disease vaccine) production workshops as well as Effluent Decontamination System (EDS) and quality inspection links supporting these workshops [8]. In June 2020, with the National Health Commission taking the lead, the General biosafety requirements for vaccine production workshops (GUOWEIBANKEJIAOHAN [2020] No.483, a national standard under approval, from now on referred to as Requirements for Workshops) was jointly issued by several ministries in China, putting forward requirements for biosafety in highly pathogenic human vaccine (typically COVID-19 inactivated vaccine) production workshops [9]. Conforming to the relevant laws and regulations of Good Manufacturing Practice of Medical Products (GMP) for human (veterinary) use, these standards specifically stipulate the requirements for the HVAC systems of high-biocontainment facilities based on the biosafety risk characteristics of large-scale industrial production workshops. See Table 1 for comparing the requirements for HVAC systems stipulated in the standards relevant to high-biocontainment facilities in China.

Table 1.

Comparison of the requirements for HVAC systems stipulated in the standards relevant to high-biocontainment facilities in China.

Index		GB 19489 [2]	GB 50346 [1]	GB 27421 [3]a	Level-3 Biocontainment Standard [8]b	Requirements for Workshops [9]c
Indoor parameters	Temperature and humidity	18℃-26℃	18℃-25℃	Not specified	As required by the GMP for veterinary use	As required by the GMP for human use.
		30 %-70 %	30 %-70 %
	Cleanliness class	Not inferior to Class 8	Class 7 or 8	Not specified	As required by the GMP for veterinary use	As required by the GMP for human use.
	Ventilation rate	≥ 12 times/h	≥ 15 times/h (for Class 7)	≥ 12 times/h	As required by the GMP for veterinary use	As required by the GMP for human use.
			≥ 12 times/h (for Class 8)
	The atmospheric pressure differential between a core room and an adjacent buffer room	As specified	As specified. The minimum negative pressure differential to rooms adjacent or connected to the outdoor direction is specified also.	As specified	As specified. The minimum negative pressure differential to rooms adjacent or connected to the outdoor direction is specified also.	As specified. The minimum negative pressure differential to rooms adjacent or connected to the outdoor direction is specified also.
Ventilation system		Independent fresh air system.	Independent fresh air system.	Negative pressure ventilation system. Buffer room may not be equipped with a ventilation system	Independent fresh air system. Air may be returned to the original (for non-zoonotic cases) area.	Independent fresh air system.
		HEPA filters are required for both air supply and exhaust systems. According to the risk assessment, set one or two stages of exhaust HEPA filters for b2 lab. For the BSL-4 lab, two stages of exhaust HEPA filters are required.	HEPA filters are required for both air supply and exhaust systems. Two stages of exhaust HEPA filters may be set as special requirements are needed for the BSL-3 lab. For the BSL −4 lab, two stages of exhaust HEPA filters are required.	HEPA filters are required for both air supply and exhaust systems.	Single HEPA filter for air supply and return (if any), and two stages of HEPA filters for air exhaust.	Single HEPA filter for air supply, and two stages of HEPA filters for air exhaust.
Integrity testing		BSL-3 lab (b2) and BSL-4 lab’s air supply HEPA filters and all of the exhaust HEPA filters shall be able to disinfect, sterilize and detect leakage (by scanning) in situ.	Exhaust systems in the BSL-3/4 lab and air supply HEPA filters in the BSL-4 lab shall be able to disinfect, sterilize and detect leakage (by scanning) in situ. A total penetration test method may be used if there is a lack of scanning conditions.	Air exhaust HEPA filters shall be able to disinfect, sterilize and detect leakage by scanning in situ. A total penetration test method may be used, if there is a lack of scanning conditions	Air exhaust HEPA filters in the containment area shall be able to disinfect, sterilize and detect leakage in situ; the detection method is not specified.	Air exhaust HEPA filters in the containment area shall be able to disinfect, sterilize and detect leakage in situ; the detection method is not specified.
Fan standby		Standby exhaust fans are required. For ABSL-3 and BSL-4 lab, standby air supply fans are required.	Standby exhaust fans are required. For ABSL-3 and BSL-4 lab, standby air supply fans are required.	Not specified	Standby air supply fans are recommended. In addition, standby exhaust fans are required.	Both standby air supply and exhaust fans are required.
Airflow pattern		The air flows from the outside to the inside, and the air in the laboratory flows from the low-risk area to the high-risk area.	The air flows from the auxiliary working area to the containment area, and the air in the laboratory flows from the low-risk area to the high-risk area.	Avoid interference and reduce eddy air and dead airflow corners in the room by setting a reasonable layout.	The air flows from the outside to the inside, and the air in the production area flows from the low-risk area to the high-risk area.	The air flows from the outside to the inside, and the air in the production area flows from the low-risk area to the high-risk area.
System reliability		In case of system failure, there shall be a mechanism to avoid pressure reversal, and the starting and stopping of indoor air exhaust equipment shall have an orderly pressure gradient and necessary stability.	There shall be adjusting measures for the air exhaust or supply system to maintain stable indoor pressure and pressure differential gradient.	No clear specification	When the exhaust system fails, there shall be a mechanism to avoid positive pressure in the containment area (orderly pressure gradient is not required).	Based on the risk assessment results, the reliability of the critical risk factors identified during the operation of the HVAC systems shall be verified.

Abbreviations: HVAC = Heating, Ventilating, and Air Conditioning；GMP = Good Manufacturing Practices；HEPA = High Efficiency Particulate Air Filter；BSL = Biosafety Level；ABSL = Animal Biosafety Level.

^aThis standard only involves biosafety levels (BSLs) and animal biosafety levels (ABSLs) 1 to 3.

^bThis standard is for level-3 biosafety only.

^cThis standard only involves two levels of biosafety, i.e., “high risk” and “low risk” levels.

2.2. Introduction to the requirements for HVAC systems in standards, specifications, and guidelines in other countries

This paper analyzes standards, specifications, and guidelines for high-biocontainment facilities developed by European and American countries and the World Health Organization. It includes the Biosafety in Microbiological and Biomedical Laboratories (6th edition, from now on referred to as BMBL-6) by the US, the ARS Facilities Design Standards (from now on referred to as ARS) by the US Department of Agriculture, the Canadian Biosafety Standards (2nd edition, from now on referred to as CBS-2), the Canadian Biosafety Handbook (from now on referred to as CBH), the Canadian Biosafety Standards and Guidelines (from now on referred to as CBSG), AS-NZS2243.3 Safety in Laboratories—Part 3:Microbiologic Safety and Containment (from now on referred to as AS/NZS 2243.3) by Australia/New Zealand, and the Laboratory Biosafety Manual (4th edition, from now on referred to as LBM-4) by the WHO [10], [11], [12], [13], [14], [15], [16], [17], [18], [19]. Started earlier than other countries in biosafety laboratory constructions, European and American countries have formed a mature biosafety construction and management system that can guide and promote the preparation and modification of biosafety facilities standards in China. Since the outbreak of the COVID-19 pandemic in 2020, the BMBL and the LBM have been updated one after another. The new versions pay more attention to biosafety culture and have specified more detailed requirements for hardware facilities.

Specifically, the new LBM-4 has replaced the biosafety level with the risk assessment framework introduced in the LBM-3, emphasizing the importance of risk assessment. However, there are still three levels of requirements in the new manual, i.e., core requirements, heightened control measures, and total containment measures. The maximum containment measures correspond to the requirements for level-4 biosafety experiments using a safety cabinet and positive-pressure protective suit. In the manual, for biosafety laboratories that adopt the full containment measures, air may be returned to the original containment area with the precondition of two HEPA filters before it is circulated to the original room only [17].

In the CBS-2 and the BMBL-6, requirements for large-scale industrial production facilities with high biocontainment have been made, but they lack a specific and clear index. In the European Biotechnology— Large-scale process and production—Plant building according to the degree of hazard (from now on referred to as BS EN 1620), qualitative requirements, such as absolute negative pressure ventilation system, HEPA filter for air exhaust, leakage detection and safe replacement of HEPA filter, are made for the plant building design of containment level 3 only [18]. In another representative European standard, Minimum Standards for Laboratories Working with FMDV in Vitro and Vivo (referred to as EuFMD) have been set up for the absolute negative pressure mechanical ventilation system for large-scale foot-and-mouth disease vaccine production workshops. It is stipulated that the HVAC systems should make the containment area absolute negative to the surrounding areas, the system may return air (to the original area only, using a HEPA filter), and the air must be exhausted through two stages of HEPA filtration [19]. See Table 2 for the comparison of the requirements for HVAC systems stipulated in standards, specifications, and guidelines relevant to high-biocontainment facilities in other countries.

Table 2.

Comparison of the requirements for HVAC systems stipulated in standards, specifications, and guidelines relevant to high-biocontainment facilities in other countries.

Standard requirement	BMBL-6 and ARS	CBS-2, CBH and CBSG	AS/NZS 2243.3[15]	LBM-4 LDM
Pressure differential	The pressure shall be lower than that of the atmosphere and the adjacent rooms, with no specific index [10], [11].	The pressure shall be lower than that of the atmosphere and the adjacent rooms, with no specific index [12], [13], [14].	For the BSL-3/4 lab, the pressure shall be at least 50 Pa below the atmosphere. For the BSL-4 lab, the pressure shall be at least 25 Pa below that of the adjacent rooms.	The pressure shall be lower than that of the atmosphere, with a guaranteed clear pressure gradient [16].
Ventilation system	A negative-pressure ventilation system is required. No specific requirements are made regarding whether air return is allowed in the BSL-3 labs. For the BSL-4 labs, a fresh air system is required [10].	An independent fresh air system is required. The ventilation system in the low-containment area (effective backdraft protection measures if used) may be shared with CL3[12]. Air is exhausted from the high-containment area to avoid being sucked back into the building [13].	The independent ventilation system is required. Air is allowed to return to the original area only. Class III biosafety cabinet shall exhaust air through the air exhaust system.	A negative-pressure ventilation system is required. For the BSL-4 lab using a safety cabinet and positive pressure suit, the air is allowed to return to the original area, but it must be filtered through two stages of HEPA filters [17].
HEPA filter design	For the BSL-3 lab, the HEPA filter is not mentioned in the air supply system but is required in the exhaust system [10], [11]. For the BSL-4 lab, HEPA filters are required in the air supply and exhaust system. A single HEPA filter is required for the cabinet laboratory. Two stages of HEPA filters are required in the exhaust system for both Class III biosafety cabinet and positive pressure suit laboratory; supply and exhaust HEPA filters shall be as near as practicable to the containment area [10].	As for air supply, an anti-backdraft device is required in CL3 and CL3-Ag, or HEPA filters are set based on risk assessment; HEPA filters are required for air supply in CL4. As for air exhaust, HEPA filters are required. A single HEPA filter is required for EDS ventilation pipes in CL3 and CL3-Ag. Two stages of HEPA filters are required in CL4; prefilters are required in the animal laboratory; single HEPA filter is required for differential pressure device in the containment area; the efficiency of HEPA filters shall not be less than 99.99 % for 0.3 μm particles [13].	For BSL-3 labs, air supply filters shall comply with Class A or B requirements in AS 1324.1, and a single exhaust HEPA filter is required. For BSL-4 labs, a signle supply HEPA filter and two stages of exhaust HEPA filters are required, and HEPA filters for air exhaust shall meet the requirements of AS 4260. Supply and exhaust prefilters shall be mounted upstream of the HEPA filters. In addition, any tubing of the pressure-sensing equipment penetrating the containment barrier shall be fitted with a 0.2 μm membrane filter.	The location of HEPA filters shall be designed with thorough consideration of factors including operation and maintenance, testing, verification, and sterilization [17]. For enhanced laboratory, a single exhaust HEPA filter is required. For BSL-4 labs, a single supply HEPA filter and two stages of exhaust HEPA filters are required [16], [17].
Integrity testing	Air exhaust HEPA filters in BSL-3 or 4labs shall be able to disinfect and detect leakage in situ[10], [11]. HEPA filtration units shall be equipped with decontamination ports and air-tight dampers [10].	HEPA filtration units shall be able to disinfect, sterilize and detect leakage (by scanning) in situ, and the air tightness shall meet the requirements of ASME N511 and AG-1 [14].	HEPA filtration units shall be able to disinfect, sterilize and detect leakage in situ. The disinfection shall meet the requirements of AS/NZS 2647, and leakage detection shall meet the requirements of AS 1807.6–7.	HEPA filters shall be able to disinfect, sterilize and detect leakage in situ. Scanning shall be used in leakage detection or otherwise be replaced regularly. The filters shall be inspected annually [17].
Fan standby	For BSL-4 labs, standby supply fans are recommended. For ABSL-3 and BSL-4 labs, standby exhaust fans are required [10], [11].	Not specified	For BSL-3 labs, redundant fans are not required, but it shall be ensured that the pressure does not reverse during failure. For BSL-4 labs, standby exhaust fans are required	For BSL-4 labs, standby exhaust fans are required [17].
Airflow pattern	There shall be a directional flow from low-risk to high-risk indoor areas to keep a differential pressure [10], [11].	Indoor directional flow is require [12].	Indoor directional flow is required. Air inlet/outlet shall not be set in a manner that would affect the use of the biosafety cabinet. The directional flow pattern shall be verified by air flow test.	There shall be a directional flow from low-risk to high-risk indoor areas, and verification is required [16].
System reliability	Supply and exhaust fans shall be interlocked. It shall be ensured that the backdraft is prevented in the containment area when a fault occurs. A visual directional flow monitoring device shall be set at the laboratory entrance, and the alarm of airflow disturbance shall be considered. UPS is required for the air supply and exhaust control and monitoring system in BSL-4 labs [10].	The ventilation system shall be equipped with effective airflow control devices. When a fault occurs, fans shall be interlocked to control pressure fluctuation, and sound and light alarms inside and outside the containment area shall be triggered simultaneously. A visual device is required to monitor the containment area's directional airflow. Class II B2 safety cabinet shall be installed so that the airflow in it does not reverse in case of ventilation system failure or exhaust fan of safety cabinets. UPS is required for the air supply and exhaust control and monitoring system [12], [13], [14].	Supply and exhaust fans shall be interlocked. A zero pressure point shall be set to ensure the pressure monitoring effect. If the pressure fluctuation of the BSL-4 lab exceeds the set value by 15 Pa over 2 min, sound and light alarms shall be triggered.	A ventilation alarm system is essential and the supply and exhaust fans shall be interlocked to prevent abnormal pressure fluctuation. In addition, there shall be sufficient security redundancy. For a positive-pressure protective suit ventilation system, a standby power supply and alarm system are required, and the ventilation system, pressure differential, breathing air system, and experimental operating system shall be monitored continuously [16], [17].

Abbreviations: BMBL = Biosafety in Microbiological and Biomedical Laboratories; ARS = Facilities Design Standards of Agricultural Research Service (ARS) by the US Department of Agriculture; CBS = Canadian Biosafety Standards; CBH = Canadian Biosafety Handbook; CBSG = Canadian Biosafety Standards and Guidelines; AS/NZS 2243.3 = Safety in Laboratories - Part 3: Microbiologic Safety and Containment by Australia / New Zealand; LBM = Laboratory Biosafety Manual by the WHO; LDM = Associated monographs of LBM: Laboratory design and maintenance; CL = Containment level; Ag = Agriculture; ASME = American Society of Mechanical Engineers; BSL = Biosafety Level; ABSL = Animal Biosafety Level; HVAC = Heating, Ventilating, and Air Conditioning; HEPA = High Efficiency Particulate Air Filter; EDS = Effluent Decontamination System; UPS = Uninterruptible Power Supply.

3. Comparative analysis of crucial point requirements

3.1. Indoor parameters of the containment area

From the comparative analysis of Table 1 and Table 2, it can be seen that China’s laboratory standards have explicit provisions and requirements on indoor temperature and humidity, cleanliness, ventilation rate, and pressure differential (negative differential pressure of the main room to the surrounding area and the adjacent rooms, negative pressure gradient to the rooms adjacent or connected to the outdoor direction). It also provides more guidance for design, detection, and accreditation. In foreign standards, only AS/NZS 2243.3 gives the pressure indicators of laboratories and adjacent airlocks, while other standards make no specific index requirements for indoor parameters, which is relatively more flexible. BMBL-6 clearly states that the designed operation parameters' certification must be carried out before operation, and the facilities shall be certified annually [20].

3.2. Ventilation system form

For high-biocontainment facilities, requirements for ventilation systems in China’s standards are consistent with those in Canadian standards, i.e., fresh air system shall be adopted, except for the allowance of the air’s return (HEPA-filtered) in the non-zoonotic veterinary vaccine production workshop, a requirement based on the European foot-and-mouth disease workshop standard [19]. The US BMBL-6 standard does not stipulate whether air return is allowed in the BSL-3 labs but requires the BSL-4 labs to be equipped with a 100 % fresh air system. AS/NZS 2243.3 and LBM-4 stipulate that even BSL-4 labs may be set up with return air systems based on risk assessment, but the return air shall be HEPA-filtered and returned only to the original area. Compared with the return air system, the 100 % fresh air system has better indoor air dilution and replacement effect, which is more safety. However, it consumes more energy than a return air system. In addition, there are hidden dangers, such as coil frost cracking in the northern cold area. The new WHO standard has made conceptual adjustments in risk grading, paying more attention to risk assessment rather than simply providing rigid “one-size-fits-all” requirements.

3.3. Filter settings

China’s standards require that HEPA filters be set in air supply and exhaust systems for high-biocontainment facilities. For laboratories in which normal-quantity air-transmitted pathogenic biological agents can not be operated by effectively using safety isolation devices (meeting the requirements of article 4.4.3 of GB 19489), it shall be confirmed through risk assessment to determine whether the exhaust adopts two-stage of HEPA filters. The latter is required for BSL-4 labs, all high-biocontainment production workshops, and ancillary supporting facilities.

In foreign systems, there are no explicit requirements for the air supply filters of laboratories of BSL-3 and below in the United States, Canada, or WHO standards. However, according to BMBL-6 of the United States, the exhausted air of BSL-3 labs shall be HEPA-filtered. Otherwise, it shall be dispersed away from the experimental area, and the fresh air position of the building; BSL-4 labs shall be provided with supply and exhaust HEPA filters, and Class III biosafety cabinets shall be provided with two stages of HEPA filters. BMBL-6 also puts forward suggestions for enhanced protection of large laboratories related to agricultural and economic animals, such as parallel standby HEPA filtration units for efficient replacement during regular operation and prefilters at air opening of the room to improve filtration efficiency and prolong the service life of the filters. In Canadian standards, anti-backflow devices rather than HEPA filters are required for the air supply of BSL-3 labs; meanwhile, ventilation pipes of EDS in the laboratories shall be set with a single HEPA filter (level-3) or two stages of HEPA filters (level-4); the filtration efficiency of all exhaust HEPA filters shall not be less than 99.99 % for 0.3 μm particles. Standard AS/NZS 2243.3 specifies the air supply filters for BSL-3 labs (AS 1324.1). It is also stipulated that the BSL-3 labs shall be provided with exhaust HEPA filters and the BSL-4 labs provided with a single supply HEPA filter and two stages of exhaust HEPA filter; pre-filters shall be mounted upstream of the HEPA filters. The standard also stipulates that the pressure sensor in the containment area shall be fitted with a 0.2 m hydrophobic membrane filter.

Comparing standard requirements, there are precise requirements for room cleanliness in China’s biosafety facilities, HEPA filters are required for all air supply systems. As a result, the requirements for indoor environments and room biosafety levels are relatively strict. However, in addition to the BSL-4 labs, foreign standards vary in the scope of air supply requirements, with varying degrees of flexibility, and are more dependent on risk assessment for determination.

3.4. Integrity testing requirements for HEPA filters or filtration units

All standards require that HEPA filters or exhaust high-efficiency filtration units be able to sterilize and leakage detect in situ. China’s standards [1], [2], [4], [6] give apparent detection and evaluation indexes and stipulate that when the scanning method of leak detection for the HEPA filter is unavailable, the total penetration test method may be used [2]. However, foreign standards do not accept the total penetration test method. LBM-4 stipulates that the HEPA filter that cannot be scanned for leakage detection shall be replaced regularly as a preventive maintenance method [17].

Based on China’s national conditions, restricted to the actual situation of some laboratory reconstruction conditions, exhaust HEPA filters often cannot be scanned for leakage detection. In addition, combined with the fact that the exhaust HEPA in Class II B2 biosafety cabinets produced at home and abroad are not available for scanning method, the Chinese standard accepts the total penetration test method, which is closer to the engineering practice. Indeed, for new projects, the design shall meet the space requirements for scanning method to the greatest extent and be in line with international standards.

3.5. Fan standby

In addition to the requirements for mobile laboratories, Chinese standards have made requirements for standby exhaust fans of high-biocontainment facilities and standby air supply fans of BSL-4 labs, animal BSL-3 labs, and workshop facilities with high-biocontainment. In foreign standards, BMBL-6 of the United States puts forward requirements for standby exhaust fans in large animal-enhanced laboratories, and BMBL-6, AS/NZS 2243.3, and LBM-4 put forward requirements for standby exhaust fans in BSL-4 labs. In addition, BMBL-6 highly recommended standby air supply fans for enhanced laboratories and BSL-4 labs. Although AS/NZS 2243.3 does not require standby fans for BSL-3 labs, it proposes that the failure mode of system operation shall be considered to ensure that there is no pressure reversal in case of failure. It can be seen that the safety redundancy of fans in Chinese standards is more conservative and has higher reliability. The increase in economic investment brought about by safety redundancy and the safety guarantee provided by reliable operation shall be balanced according to scientific risk assessment.

3.6. System reliability requirements

In addition to the requirements for mobile laboratories, China’s standards stipulate the reliable operation of air conditioning systems. Its main idea is to ensure the systems can meet the most basic biosafety requirements when different working conditions change (often when the biosafety risk is the highest). It includes (but is not limited to) system start-up, operation and shutdown, room ventilation equipment start-up and shutdown, standby supply/exhaust fan switching and standby power supply switching, etc. Moreover, for the severe cold areas in the north, the reliability of the heat source supply for operation in winter shall be fully considered, which means that full consideration shall be given to the anti-freezing of the coil, the redundancy of heating and transmission system of heat exchange station under the requirements of continuous and stable operation of the laboratories in winter.

Although there are some differences in the expression of foreign standards, the elements involved are roughly the same. The American and Canadian standards only put forward UPS requirements for the ventilation and air conditioning systems of BSL-4 labs; LBM-4 puts forward standby power supply requirements for BSL-4 labs. In addition, the Canadian standards emphasize that the installation of Class II B2 biosafety cabinets shall ensure that the airflow in it will not reverse in case of failure of the ventilation system or the exhaust fan of the cabinets. The standard AS/NZS 2243.3 emphasizes the set requirements for a “zero pressure” reference point to ensure the stability of the pressure monitoring effect. It requires audio and visual alarms for pressure fluctuation exceeding the set value by 15 Pa for over 2 min in BSL-4 labs, which can be used as a reference for the design, construction, operation, and maintenance of laboratories in China.

4. Conclusions and prospects

4.1. Risk assessment is of mutual referential significance

Although the specific provisions of the HVAC systems in domestic and international biosafety standard systems are different due to different national conditions and cultural differences, their essence is determined based on the concept and logic of risk assessment, which is of mutual referential significance.

First, identify the biological hazard factors that may occur in the operation of the HVAC systems, such as fan failure, power failure, HEPA filter damage, leakage, etc. Secondly, analyze the identified risks, judge the probability of occurrence and the severity of these hazards after the occurrence, determine the biosafety level and evaluate it. Third, take corresponding effective measures to reduce these risks. Finally, analyze the effectiveness of risk measures and whether the residual risks after taking measures are acceptable as the final risk assessment results. Take the HEPA filter as an example, leakage can be considered the most severe biosafety risk. Therefore, domestic and international standards stipulate that HEPA filtration is required to exhaust BSL-3 and above biosafety facilities. The HEPA filter should be capable of in-situ disinfection, sterilization, and leak detection. Some more critical occasions, such as sizeable animal-enhanced BSL-3 laboratories and (A)BSL-4 laboratories, require two HEPA filters connection in series to ensure the reliability of biosafety.

4.2. China’s biosafety standards are instructive in terms of facility construction and operation

Compared with other countries, China’s biosafety standards are mostly national (industrial) standards or specifications, with more specific and detailed indexes and binding forces for enforcement, which are more instructive in facility design, construction, detection, and operation and maintenance management. However, since the specific indexes are specified in the national standards and must be met, there is inevitably a lack of flexibility in the implementation process, which is in line with the national conditions and necessary in the early stage of the development of laboratory biosafety in China. However, with the development and progress of society, it needs to be further dialectically treated. Therefore, GB 50346 lays more emphasis on the hardware of the laboratory. GB 19489 gives more detailed and extensive indexes, providing hardware guarantees for realizing the laboratory requirements.

Biosecurity Law of the People’s Republic of China stipulates that enterprises’ biosafety management of production workshops involving pathogenic microorganism operations shall be carried out following the relevant provisions of the laboratories of pathogenic microorganisms and other biosafety management specifications [7]. Therefore, the two workshop standards, based on lab standards, make corresponding provisions in combination with the characteristics of large-scale production in the workshops and their respective GMP requirements. The “Level-3 Biocontainment Standard” of the Ministry of Agriculture and Rural Affairs focuses more on hardware facilities and does not involve the relevant provisions of risk assessment and management system, which is mainly the basis for engineering design, construction, and inspection, and acceptance of Level-3 protection hardware facilities. The standard “Requirements for Workshops” issued by the National Health Commission refers to GB 19489 on the framework and has clear risk assessment and management system provisions. In addition, due to the higher biosafety risks involved, the corresponding hardware facilities and equipment indicators are relatively more stringent.

4.3. International standards are more flexible in the implementation of projects

International standards are mostly manuals or guidelines, mainly based on qualitative principles, which are more flexible in the implementation of projects. Among them, BMBL-6 of the United States and LBM-4 of WHO are the universal guidelines and principles universally acknowledged in laboratory biosafety, playing a leading role in the field of international biosafety [21]. In the new version of BMBL-6, content related to biosafety culture has been added. The content related to biosafety cabinets, arthropod laboratories, large-scale cultivation, and laboratory sustainability (energy conservation) research has been updated, added, or improved with broader coverage. Conceptual adjustments in risk grading have been made in the new WHO standard, which emphasizes risk assessment more than the rigid “one size fits all” requirements. The new WHO standard considers the conditions of different countries and regions in Asia, Africa, and Europe and is more adaptable to a broad spectrum. It is also significant to developing similar laboratory standards in China. Canadian standards have not been updated in recent years, but from the comparative analysis of regulations and indicators, they are still relatively stringent standards worldwide. AS/NZS2243.3 pays more attention to agriculture regarding provisions and contents, mainly related to regional economic and geographical characteristics.

4.4. HVAC systems construction standards need to apply to different functional characteristics

With the development of the times, some unique and complex high-biocontainment facilities have gradually been introduced to people, such as plant laboratories, arthropod laboratories, laboratories of special scientific instruments (such as cryoelectron microscopy and animal nuclear medicine), and laboratories with special functions (such as human anatomy). Therefore, it is necessary to determine their HVAC systems construction standards based on different functional characteristics. At present, China’s General Requirements for Plant Biosafety Laboratory has already been released, and the compilation of relevant standards for other complex types of laboratories is still in the stage of exploration and development, which can be carried out by referring to international standards and combining with China’s national conditions.

4.5. Application of digital and intelligent technology is the trend in high-biocontainment facilities

In the future, we shall focus on applying digital and intelligent technology in high-biocontainment facilities, especially HVAC systems, to improve the safety and reliability of system operation. Furthermore, the high energy consumption characteristics of similar projects, and in combination with the national strategy of “carbon peak and carbon neutrality”, we should vigorously carry out the intelligent operation and maintenance of HVAC systems of high-biocontainment facilities, the research and development of energy-saving technology and the establishment of the standard system.

Conflict of interest statement

The authors declare that there are no conflicts of interest.

Author contributions

Lei Liang: Conceptualization, Data curation, Writing – original draft. Xinfang Hong: Conceptualization, Data curation, Writing – original draft. Bing Lu: Formal analysis, Validation. Xuedong Yu: Formal analysis, Validation. Guoqing Cao: Formal analysis, Validation. Xin Feng: Formal analysis, Validation. Quan Zhou: Formal analysis, Validation. Yanqin Wang: Formal analysis, Validation. Donglai Wu: Formal analysis, Validation. Rong Wang: Methodology, Supervision, Writing – review & editing.