Institute for Historical Review
A fumigation facility, whether a building or a chamber, must adhere to the same basic requirements. It must be sealable, heatable, have both circulation and exhaust capability for the air, must have a sufficiently high stack for the exhaust and a means for distribution of the gas evenly (likewise the Zyklon B material).
First, if a chamber is used today, it must be a welded and pressure tested vessel coated with an inert (epoxy) paint or stainless steel or plastic (PVC). The doors must be gasketed with an HCN resistant material (pickled asbestos, neoprene or Teflon®). If a building, it must be made of brick or stone and coated both inside and out with an inert (epoxy) paint or pitch, tar or asphalt. The doors and windows must be gasketed or sealed with a rubberized or pitched canvas and sealed with neoprene sealant or tar. In either case, the area must be extremely dry. The term 'sealing' has two meanings: first, to mechanically prevent leakage from the facility; and second, to render the exposed, porous surfaces of the facility impervious to impregnation by Zyklon B gas.
Second, the chamber or structure must have a gas generator or distribution system for Zyklon B which would force hot air over the Zyklon B or the generator (generator may be heated with water if sealed) and circulate the warm air and gas. The mixture required for fumigation is 3200 parts per million (ppm) or 0.32% total volume HCN. The chamber must be free of obstructions and have a capability for a strong, constant and copious air flow.
Third, the chamber or structure must have a means for evacuating the poisonous air/gas mixture and replacing it with fresh air. Generally, this is done with an exhaust or intake fan with either exhaust or intake valves or louvered ports of sufficient size to allow reasonable air change per hour. Usually, a sufficient cubic feet per minute (cfm) fan and intake and exhaust aperture should permit a complete air change in 1/2 hour and should be run for at least twice the required time of one hour, or two hours. The larger the facility, the less practical this becomes (due to the size of available fans) and exhaust times may take several hours or longer.
The exhaust must be vented at a safe distance above the facility where the air currents can dispense the gas. This is normally 40 feet above the structure, but it should be more if the structure is sheltered from the wind. If an incinerator is used, the stack may be only several feet in height. It is generally too costly to incinerate the HCN because of the air volume it must handle in a short time period.
The temperature of the walls and the air within the facility, and the intake air, must be kept at least 10 degrees above the boiling point of the hydrocyanic acid (78.3 degrees F) to prevent condensation of HCN on the walls, floor and ceiling of the facility, as well as in the exhaust system. If the temperature is below 79 degrees F and condensation occurs, the facility must be decontaminated with chlorine bleach or ammonia, the former being the most effective. This is accomplished by spraying the walls either automatically or manually. If done manually, protective suits (generally neoprene) must be worn and the technicians must utilize air breathing cylinders, as gas masks are unsafe and dangerous. The interior of the building must be evacuated longer to allow the chlorine bleach vapors to neutralize the liquid HCN in the exhaust system. The interior of the building must be washed with water and thoroughly mopped and dried before the next use.
Additionally, a check of the air inside the building must be done to determine whether all of the HCN has been removed. The test may be either by gas detector or by the copper acetate/benzidene test. In the former, an electronic readout is provided with detection to 10 ppm. In the other, a benzidene solution is mixed with a copper acetate solution and is used to moisten a piece of test paper which turn blue in varying degrees if HCN is present.