History
      As long as 80 years ago it was recognized that hydrocyanic acid could be useful in pest control but it took half this time to popularize the method.
      Deficiencies and disadvantages had first of all to be eliminated from the method of application. First this had been done in such a way that hydrocyanic acid was no more developed on the spot by mixing cyanides and acid, but this process already took place in the factory: The so-called "pot method" was replaced by liquid hydrocyanic acid. The few deficiencies of this procedure were removed in the early twenties by the ZYKLON method: One added liquid HCN to a "carrier substance", thus simplifying handling whilst all favourable properties of liquid HCN were maintained. At the same time, danger to the operator was reduced to a minimum. Hydrocyanic acid in the form of ZYKLON can be safely stored for considerable periods and under all climatic conditions, any quantity of gas can be easily measured, quickly and cleanly released. Any residures are completely harmless.

Composition
      In ZYKLON pure (98%-99%) liquid hydrocyanic acid is chemically stabilized and absorbed in a porous, inert material. It is supplied in snippets or discs prepared from wood pulp. Snippets generally are preferred as in view of their larger surface they give off the gas more rapidly. Upon request also discs can be supplied. The aborbent material can easily be collected at the end of the fumigation.

Packing
      ZYKLON is packed in handy, gas-tight tins of various sizes which are packed in strong wooden cases. One case, measuring 72 x 50 x 36 cm contains:
      Imperial - units 16 tins, each containing 40 ozs. HCN - total 40 lbs HCN or 30 tins, each containing 16 ozs. HCN - total 30 lbs HCN.

Toxicity
      No thoroughly effective pesticide is known to exist which could be considered to be harmless to human beings or mammals. Fatal concentrations of HCN impede or completely cut off the oxygen supply to the cells. The poison can enter the body in three ways: through the mouth, the respiratory organs, or the pores of the skin. The latter will occur in particular if the body is exposed to high concentration for any length of time and in unfavourable conditions (great heat).

Methods
      Prior to fumigation, the tins must be distributed about the building. The tins are opened, and the ZYKLON is scattered so as to reach even the remotest parts of the building. If this is done correctly the gas will develop evenly and instantaneously throughout the premises. Spaces difficult to reach may be charged separately. In multi-storied buildings one begins with the top floor, and then works towards the exit, taking care that nobody re-enters rooms already charged. Even under mask protection it is not advisable to expose oneself to the gas more than is absolutely necessary. The exit door is sealed after everybody has left the building; warning notices must be put up before gassing commences and a guard placed near the building to prevent unauthorised persons from entering. Time of exposure depends on the type of pests to be attacked; for the destruction of the various types of moths and their pre-adult stages 24 hours will suffice, against other kinds of insect pests one should fumigate for 48 hours. If there are any dense stowages or bulkss of commodities to penetrate, the time of exposure may need to be extended to 72 hours.

Ventilation
      During this operation gas-masks must be worn. The ventilation takes place in the reverse direction to the gassing. All windows near the entrance are opened first, then gradually those in the rest of the building. It is advisable to work only for 10 to 15 minutes at a time and then to make interruptions of half an hour, as a precaution against skin poisoning.
      Depending on concentration, outdoor tempature and weather conditions, ventilation will take at least 10 hours. Clearing of tins and residues may be commenced before the end of airing. Windows and doors must remain open, and gas-masks kept available. ZYKLON tins and absorbent material must always be collected and cleared away before the resumption of work.