Table 2. Comparison of fumigants used for decontaminating MSCs.
| Property | Formaldehyde Gas (CH 2 O) | Hydrogen peroxide vapor (VHP; H2O2) | Chlorine dioxide gas 3 (ClO2) |
|---|---|---|---|
| Toxic | Yes (by inhalation, skin contact and ingestion) | Yes (skin and eye irritant) | Yes (by inhalation, also skin, eye and mucous membrane irritant) |
| Carcinogenic | Yes | No | No |
| Long term exposure limit 1 (p.p.m.) | 2.0 | 1.0 | 0.1 |
| Short term exposure limit 1 (p.p.m.) | 2.0 | 2.0 | 0.3 |
| Corrosive | No | Yes (with nylon, cellulose, copper, lead, iron oxide, epoxy) | Yes (if chlorine gas is present) |
| Sealing of MSC | Air tight seal required | Air tight seal not required | Air tight seal required |
| Access to lab during fumigation of MSCs | Not permitted due to leakage danger | Permitted | Not permitted due to leakage danger |
| Penetration of HEPA filters | Yes | Not a true gas so may not penetrate HEPA filter | Yes |
| Humidity requirement (RH) | Above 60% | 30% (Steris2), ambient (Bioquell2) | Above 60% |
| Residue | Yes (paraformaldehyde and methenamine–requires extensive cleaning) | No | Minimal (NaCl) |
| Approximate decontamination time per cabinet (hours) | 11–17 | 3–10 | 3–4 |
| Relative cost | Cheap (no specialist equipment required) | More expensive (specialist equipment required) | More expensive (specialist equipment required) |
| Advantages | Cheap Non-corrosive Current industry standard method | Safe by-products and no residue Relatively fast Automated | Safe by-products and minimal residue Best sporicide |
| Disadvantages | Slow with added clean up time due to residue formation Carcinogen | Some corrosion issues Vapour may not penetrate HEPA filters Instability of VHP | Highly toxic Some corrosion issues with metals |
| Overall effectiveness | Good | Good | Good (best sporicide) |
Notes: This table compares the three fumigants most commonly used in the laboratory to decontaminate MSCs (also refer to the studies by Czarneski and Lorcheim (2011) and HSE (2005b)). MSCs that are being used for clean cell culture work will only need to be fumigated following any episodes of microbial contamination attributed to the cabinet and before changing filters, servicing, moving or disposing of the cabinet, depending on local rules and risk assessment. Decontamination of MSCs using toxic fumigants is a potentially hazardous process and should only be performed by fully trained members of staff using the appropriate personal protective equipment and following detailed Standard Operating Procedures and Risk Assessments. For those laboratories not equipped to undertake fumigations several companies that supply MSCs also offer a contract fumigation service.
Long- and short-term exposure limits as defined by the UK Health and Safety Executive (2005).
Steris (www.steris.com) and Bioquel (www.bioquell.com) are two commonly used commercial suppliers of hydrogen peroxide generators and associated equipment required for VHP fumigation. MSCs must be fitted with the correct ports.
Chlorine dioxide fumigation requires a chlorine dioxide generator and associated equipment available from several companies in the UK including SafeOx (www.safeox.com) and Activ-Ox (www.activox.org). MSCs must be fitted with the correct ports.