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On occasions it will be necessary to decontaminate safety cabinets using a fumigation technique. This might be a routine procedure or performed if maintenance work is to be carried out. Alternatively, fumigation might be an emergency procedure if, for example, there has been a spillage of infectious material. Fumigation is achieved by release of vapour, this is usually Vapourised Formaldehyde but vaporised Hydrogen Peroxide (VHP) can be used as an alternative.
Fumigation should always be a planned exercise with suitable controls in place and with appropriate information and warnings provided for those who need to know. Only designated personnel, who are fully trained, should carry out fumigation operations - following an agreed procedure. Only a fumigant and method known to be effective should be used.
Required controls:
- Containment - fumigant should only be generated within a safety cabinet, with the sash/night door securely sealed and the non-return valve closed
- Extraction - After a time period appropriate for the chemical to be effective, the fumigant should be exhausted to atmosphere by switching on the cabinet fan. Air from the room must be allowed to enter the cabinet. In the case of recirculating cabinet, ensure that the fumigant is also fully evacuated from the laboratory using the ventilation system before anyone re-enters the room
- Segregation - Before venting a hazardous fumigant to atmosphere it is essential to ensure that no personnel (for example engineers or contractors) are in the vicinity of the exhaust outlet and that the exhaust air does not enter nearby windows or air intakes
- PPE - Consider the PPE that may be required for fumigation operations, this includes gloves, lab coat, safety glasses if you need to prepare solutions but may also include wearing an appropriate face mask
- Timing - fumigate at the end of the working day or outside of normal working hours to reduce the potential for accidental exposure to vapour
- Information - Inform relevant personnel in your laboratory and any neighbouring areas, in person and/or by email. You must also place a clear and legible sign on the laboratory door to warn people that fumigation is taking place (indicating time and date)
- Documentation - Include fumigation operations (hazards, who might be harmed, control measures etc.) in an existing risk assessment, or create a new one
Comparison of fumigants
The use of Vapourised Hydrogen Peroxide offers several advantages over traditional Formaldehyde fumigation:
- Hydrogen Peroxide vapour is non-carcinogenic
- A much lower contact time is required (around 1-3 hours compared with over 6 hours using Formaldehyde)
- Hydrogen Peroxide vapour is less sensitive to temperature variation (vapour phase range is 4-80°C)
The results of a recent independent study at Porton Down indicated that both Formaldehyde, when used under appropriate conditions and Vapourised Hydrogen Peroxide were effective against a wide range of biological agents, though both had poor activity against prions. The action of both disinfectants was affected by ambient temperature with efficacy reducing at low temperatures.
The action of Vapourised Hydrogen Peroxide was adversely affected by the presence of blood in the original solution. Formaldehyde was also affected, but to a lesser extent. Vapourised Hydrogen Peroxide efficacy was also reduced by the presence of organisms which produce catalase, which does not occur with Formaldehyde.
The overall conclusions for both Formaldehyde and VPHP were that efficacy is dependent on:
- Composition of suspending fluid
- Microbial concentration
- Presence of protective agents
- Pre-cleaning (or disinfection) before fumigation - this reduces microbial concentration and dilutes any protective agents
Taken together, available evidence indicates that the efficacy of Vapourised Hydrogen Peroxide is at least equivalent to that of Formaldehyde in most cases, but the potential for reduction in effectiveness due to the presence of catalase inhibitors or protective organic material must be taken into account. To prove the effectiveness of either fumigant against the organisms in use, validation using spore strips may be necessary.
Comparison of hazards
Formaldehyde is a hazardous substance, classed as corrosive, it causes burns. It is also very toxic by inhalation, ingestion and skin absorption. It is readily absorbed through skin; may cause damage to kidneys; may cause allergic reactions; may cause sensitisation; may cause heritable genetic damage.
Hydrogen Peroxide is less hazardous: The vapour is an irritant of the eyes, mucous membranes and skin and may cause lung irritation if inhaled. Skin contact with liquid Hydrogen Peroxide can cause temporary bleaching of the skin or redness and blisters if not washed away.