8.4 Local Environmental Decontamination

Surfaces can be decontaminated using a solution of bleach; a solution containing 5,000 ppm available chlorine may be suitable for general environmental sanitation, but stronger solutions (10,000 ppm) are recommended when dealing with high-risk situations.  For environmental decontamination, formulated solutions containing 3 percent hydrogen peroxide make suitable substitutes for bleach solutions.  

Rooms and equipment can be decontaminated by fumigation with formaldehyde gas generated by heating paraformaldehyde or boiling formalin. All openings in the room (i.e. windows, doors, etc.) must be sealed before the gas is generated.  Fumigation should be conducted at an ambient temperature of at least 21°C and a relative humidity of 70 percent.  The gas should be in contact with the surfaces to be decontaminated for at least 8 hours. After fumigation, the area must be ventilated thoroughly before personnel are allowed to re-enter. Appropriate respirators must be worn by anyone entering the room before it has been ventilated and the “two-person” rule should apply.  Gaseous ammonium bicarbonate is used to neutralize the formaldehyde.  

Fumigation of spaces with a vaporous solution of hydrogen peroxide is an effective decontamination method and can be used as an alternative to paraformaldehyde.  Relatively low concentrations of hydrogen peroxide (1 milligram/liter) can be effective area fumigants.  As with any disinfectant, the efficacy of hydrogen peroxide will vary depending on the contaminating organism, the presence of organic and/or inorganic material and on the type of surface being decontaminated.  One advantage over paraformaldehyde is that the residual vapor of hydrogen peroxide decomposes into water and oxygen.  Contact EHS’s Biosafety Office if you have any questions or concerns.