Understanding ‘Airtight’ and ‘Gastight’ in Relation to the Design and Construction of BSL-3 and BSL-4 Facilities

Containment Talk 7.

Containment Talk articles discuss risk and safety issues in and around microbiological and biomedical laboratories (BSL-2, 3 and 4). Feel free to contact me via LinkedIn messaging if you have any questions or comments about laboratory safety, biosafety, biocontainment, design & equipment, engineering, etc.

Containment Talk article no. 7 takes you on a journey into the wilds of airtight, gastight and similar, poorly defined terms used in every BSL-3 and BSL-4 design, construction, and retrofit project. What does airtight, gastight mean for doors, wall-integrated equipment or penetrations? A simple and practical solution to this problem is presented.

1. Containment Leaktightness Requirements

There is often a lack of understanding of what containment boundary integrity is needed for and how to achieve it. However, this is important in order to build and deliver to the owner and users a facility that meets the applicable regulations or guidelines and is neither under- nor over-engineered.

Biosafety regulations and guidelines (e.g., [1] - [7]) use terms such as leaktight, hermetic, airtight, sealed or sealable to describe the necessary integrity or leaktightness of the containment boundary for fumigation. The purpose of containment integrity is twofold: to prevent leakage of the chemical decontaminant used for fumigation for health and safety reasons, and to contain the necessary concentration.?

Formaldehyde gas was often used for fumigation, but because it is classified as a carcinogen, it has been replaced by hydrogen peroxide, chlorine dioxide and other chemicals that still pose a health and safety hazard [8], [9].

The challenge for the consultant and the building owner is to translate vague terms such as sealed, air/gastight or leakproof into defined quantitative air permeability or leakage rates that can be verified.

2. Containment Integrity for Fumigation

For the purposes of fumigation, the containment includes not only the boundary of the work area with walls, ceiling, floor, doors and vision panels (Figure 1), but also personnel and material airlocks, media and service penetrations, wall-integrated equipment (pass-through box, pass-through autoclave) and, if available, the effluent decontamination system.

Segments and elements of the ventilation system that need to be fumigated from time to time must also be considered (Figure 1, item 2). This topic will be discussed in a later Containment Talk.

3. Leaktightness Terminology

The terms airtight, gastight, hermetic, etc. should not be used to describe the leaktightness of the BSL-3 and BSL-4 boundary. They may cause confusion and misunderstanding.

Instead, designers and builders of BSL-3 and BSL-4 facilities need to start looking at leakage or air permeability rates. For example, EN 12207:2017 [11] defines air permeability and classification for doors and windows. Manufacturers of BSL-3 and BSL-4 wall-integrated equipment and media and service penetrations will have their products certified to a tightness standard such as VDI standard 2083-19:2018 [12]. If they advertise their products as airtight and gastight only, it is essential to ask for the leakage rates and the corresponding certificates with the leaktightness classification.

4. Leaktightness Standards and Test Methods

There are two methods for testing the leaktightness of a room or containment boundary as shown in Figure 1.

1. Pressure decay test (pressure drop and pressure rise test): Measurement of the increase or decrease in pressure starting from the initial value over a period of time.
2. Pressure holding test (leakage air volume flow test): Measurement of the air leakage at a constant room pressure.

The pressure decay test is described in the Canadian Biosafety Handbook [10]. The pressure holding test in the Australian/New Zealand Standard [6] and the VDI standard 2083-19:2018 [12]. Ziegler and Tremblay [13] have published a review and discussion on BSL-3 boundary leaktightness standards and test methods.

The pressure decay test is used in Canada and in the United States for facilities with ‘gastight’ doors. This method and the Australian/New Zealand method do not consider the surface area or volume of the space being tested.

In contrast, the VDI standard [12] relates the permissible leakage rate to the area per m2 as shown in an excerpt from the standard in Table 1.

The VDI standard has two benefits:

• Definition of a proven test method and leaktightness classification for cleanrooms, BSL-2, BSL-3 and BSL-4 containments;
• A planning tool for determining the permissible leakage rates of structural components, penetrations and wall-integrated equipment.

Designers and builders use the standard to calculate the so-called ‘leakage budget’ for each room or space in the containment in two simple steps.

1. For example, a small BSL-3 laboratory room measuring 7m x 3.5m x 2.8m (L?x?W?x?H) has a surface area of approximately 108 m2.
2. According to VDI 2083-19 class 4, the permissible leakage rate at 500 Pa is 0.204 m3·m-2·h-1 (Table 1). The leakage budget for the room is 108 m2 x 0.204 m3·m-2·h-1 = 22.03 m3·h-1. The leakage rate for each boundary component is then summed. If the sum is well below the leakage budget, containment integrity is guaranteed.

For example, a class 4 door according to EN 12207 has a maximum leakage rate of 9 m3·m-2·h-1 at 500 Pa. A door with a surface of ca. 2 m2 leaks approximately 18 m3·h-1and therefore almost uses up the leakage budget.

However, if the risk assessment and fumigation strategy consider the door to be sealed for fumigation by taping it, then this door or a door with an even higher leakage rate is compliant. Note: To comply with the terms ‘sealed’ or ‘leaktight’ for fumigation, this consideration only applies to doors, not to other penetrations.

In essence, the decision as to the acceptable or permissible leakage rate of a door may depend on several factors:

1. Legal requirements (‘airtight’ or ‘gastight’ door is required by law)
2. Risk assessment
3. Fumigation strategy and frequency
4. Robustness and durability requirements
5. Cost and maintenance (CAPEX and OPEX)
6. Other factors

Note: If regulations explicitly require an ‘airtight’ or ‘gastight’ door, the VDI 2083-19 air permeability rate should meet class 4 and class 5, respectively.

5. VDI 2083-19: Test Method

The blower door test method or, alternatively, ports or couplings are used to determine the air leakage rate. This test is performed by closing supply and exhaust-air shut-off dampers for the respective room.

The blower door test is performed for each door at the containment boundary and for all internal compartment doors as defined in the risk assessment and the fumigation strategy [12], [14].

As an alternative to the blower door test method, ports or couplings on the ?room walls or at the ducts can be used (see Figure 1, no. 3). In this case, the door is sealed by taping if it is leaking due to its design.

Experience has shown that test pressures below 125 Pa lead to difficulties and inaccurate measurements due to the high tightness of the BSL-3 rooms [13].

The test for a room or a zone is passed if the limits of leak tightness class 4 at +250 Pa or higher and at -250 Pa or lower (BSL-3) and class 5 +500 Pa or higher and at -500 Pa or lower (BSL-4) are complied with [12].

6. Conclusion

The VDI 2083-19:2018 standard is a versatile tool and practicable method and has become the leading standard for the design and testing of BSL-3 and BSL-4 facilities in Europe and elsewhere.

7. References

[1]????? WHO (2020). Laboratory biosafety manual, fourth edition. Geneva: World Health Organization; (Laboratory biosafety manual, fourth edition and associated monographs). Internet: https://www.who.int/publications/i/item/9789240011311. Accessed February 2024.

[2]????? Directive 2009/41/EC of the European Parliament and of the Council on the contained use of genetically modified micro-organisms. Internet: https://eur-lex.europa.eu/eli/dir/2009/41/oj. Accessed February 2024.

[3]????? Directive 2000/54/EC of the European Parliament and of the Council of 18 September 2000 on the protection of workers from risks related to exposure to biological agents at work (seventh individual directive within the meaning of Article 16(1) of Directive 89/391/EEC) consolidated 26. Apr. 2020. Internet: https://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX%3A32000L0054. Accessed February 2024.

[4]????? PHAC (2022). Canadian Biosafety Standard, 3rd ed. Internet: https://www.canada.ca/en/public-health/services/canadian-biosafety-standards-guidelines/third-edition.html. Accessed February 2024.

[5]????? BMBL (2020). Biosafety in Microbiological and Biomedical Laboratories (BMBL) 6th Edition. HHS Publication No. (CDC) 300859. Internet. https://www.cdc.gov/labs/BMBL.html. Accessed November 2022.

[6]????? AS/NZS 2243.3:2022. Safety in laboratories Microbiological safety and containment. Internet: https://infostore.saiglobal.com/en-us/standards/as-nzs-2243-3-2022-117305_saig_as_as_3202662/. Accessed February 2024.

[7]????? Singapore Standard SS 696:2023. Specification for high containment (biosafety level 3) facility. Internet: https://www.singaporestandardseshop.sg/Product/SSPdtDetail/3403e047-1f79-4d81-be8a-c0a377a1f403. Accessed February 2024.

[8]????? Kümin D. et al. (2020). The hitchhiker’s guide to hydrogen peroxide fumigation, part 1: introduction to hydrogen peroxide fumigation. Internet: https://doi.org/10.1177/1535676020921007. Accessed February 2024.

[9]????? Kümin D. et al. (2021). The Hitchhiker’s Guide to Hydrogen Peroxide Fumigation, Part 2: Verifying and Validating Hydrogen Peroxide Fumigation Cycles. Internet: https://doi.org/10.1089/apb.21.921099. Accessed February 2024.

[10]?? PHAC (2016). Public Health Agency of Canada. Canadian Biosafety Handbook. ISBN: 978-1-100-25773-0. Internet: https://www.canada.ca/en/public-health/services/canadian-biosafety-standards-guidelines/handbook-second-edition.html. Accessed February 2024.

[11]?? DIN EN 12207:2017. Windows and doors - Air permeability – Classification. Available from Schweizerische Normen-Vereinigung, SNV, 8404 Winterthur. Internet: https://connect.snv.ch/de/din-en-12207-2017. Accessed February 2024.

[12]?? VDI (2018). VDI 2083, Sheet 19. Cleanroom technology - Tightness of containments - Classification, planning and testing. VDI Society for Construction and Building Technology (GBG). Available from Schweizerische Normen-Vereinigung, SNV, 8404 Winterthur. Internet: https://connect.snv.ch/de/vdi-2083-blatt-19-2018. Accessed February 2024.

[13]?? Ziegler, C. & Tremblay, G. (2023. Boundary Integrity Testing of Containment Level 3 (Biological Safety Level 3) Laboratories. Appl. Biosafety. Internet: https://doi.org/10.1089/apb.2023.0017. Accessed February 2024.

[14]?? EN ISO 9972:2015-12. Thermal performance of buildings; Determination of air permeability of buildings; Differential pressure method. Internet: https://www.iso.org/standard/55718.html. Accessed February 2024.