Safety Requirements for the Safe Use of Hydrogen-Cyanide for the Fumigation of Ships noted in U.S. Public Health Reports [See especially Volume 46, Nos. 27, 28, 29, 30, 35, and 36] [The following example is from No. 27 (July 3, 1931) pages 1572 and 1573:]

SOME ASPECTS OF SHIP FUMIGATION

By J R RIDLON, Surgeon, United States Public Health Service

THE FUMIGATION of ships for the destruction of rodents is a problem which has received much study and attention from various officers of the Public Health Service. The use of suitable cyanogen products has practically replaced the use of sulphur in fumigation at all of the quarantine stations of the larger ports.

Several cyanogen products have been used at San Francisco during the past few years. These, together with the methods, include the following:

1. The generation of straight hydrocyanic-acid gas by a mixture of sodium cyanide, sulphuric acid, and water.

2. The generation of hydrocyanic-acid and cyanogen-chloride gas by a mixture of sodium cyanide, sodium chlorate, hydrochloric acid, and water.

3. Liquid hydrocyanic acid and either cyanogen chloride or chloropicrin as a warning gas.

4. Zyklon-B, which consists of an earthy substance impregnated with liquid hydrocyanic acid and marketed at present with 5 per cent chloropicrin as a warning gas.

The two latter methods of fumigation afford a saving in time and labor and have almost entirely displaced the generation methods at the San Francisco station. Generation of cyanide gas on shipboard with the use of crocks and barrels was a laborious process.

[...]

["Richard Widmann" supplied the US document excerpted here; for a similar British document from Public Record Office file BT.217/548, see elsewhere on this Website].