Seal off the hood or room. Never allow personnel in the environment when the hood is being decontaminated, as highly toxic agents are used. Place boundary tapes or other obvious notices to alert anyone that they are not to approach or attempt to operate the hood until decontamination is complete. Notify the institution's safety officers of the date and time that the decontamination is to be done, as well as the type of fumigation agent being used (formaldehyde or hydrogen peroxide).
Prepare the hood. Switch the hood on but turn the hood's internal fans off. (This step will not be necessary in some hood models, so check with your manufacturer.) If the safety alarms are triggered, simply mute these. If your hood model uses a "night door," place this in the opening between the base of the hood and the bottom of the sash window and secure it into place. Attach a sign to warn employees that the hood is being fumigated. If a permit-to-work is required then attach this to the hood. Close all manual dampers. (These devices control the airflow.)
Prepare the fumigation solution and begin procedure. Into the boiler, mix equal portions of formalin and water, e.g., 30 milliliters of formalin and 30 milliliters of water. This amount can be increased or decreased according to the type, size and manufacturer of your specific hood; check the specifications before beginning. The boiler will have one tube that can be fitted tightly into the side wall of the hood. Do so and then plug it into an electrical socket. Check that all openings in the hood are tightly sealed; duct-tape them if necessary. Then start the boiler. Leave to fumigate for at least 16 hours, or overnight.
Purge the hood. After the fumigation is complete, switch the cabinet on. If dampers were previously fitted, open them and remove rubber bungs on night doors. Wait until the extraction fans have started. Then slowly remove the night door completely. Keep the hood operating with the fan running for at least two hours. The hood is ready to use after this. Wipe down the fumigation boiler with damp laboratory wipes.