Zyklon B was a common cyanide pesticide. During WW2, Germans used it to delouse fabrics at concentration camps, because of the typhus epidemic that raged across Eastern Europe from 1941.
Typhus was the primary cause of death in German WW2 concentration camps, the vast majority near the end of the war as German society collapsed.
For example, Anne Frank and her sister, Margot, died from typhus in the camp hospital at Bergen-Belsen. 15,000 of the 50,000 Jews who died in Bergen-Belsen died AFTER it had been liberated and put under quarantine by British troops.
>Nearly 14,000 prisoners would die after liberation.
iwm.org.uk/history/the-liberation-of-bergen-belsen
Americans used Zyklon B to fumigate the clothes of Mexican immigrants at the border.
>Zyklon B arrived in El Paso in the 1920s courtesy of the US government. In 1929, for example, a Public Health Service officer, J.R. Hurley, ordered $25 worth of the material–hydrocyanic acid in pellet form–as a fumigating agent for use at the El Paso delousing station, where Mexicans crossed the border from Juárez.
thenation.com/article/zyklon-b-us-border/
Zyklon B was also used for a variety of purposes by the British Empire, including fumigating passenger ships and food granaries, as discussed in these journals.
>During the past three years various products such as Zyklon B have been used in Colombo in the fumigation of vessels, lighters, granaries, rat burrows
journals.sagepub.com/doi/pdf/10.1177/146642403705800209
>A Report on the Disposal of Zyklon-B Residue following the Fumigation of the Holds of Vessels
jstor.org/stable/pdf/4578621.pdf?seq=1#page_scan_tab_contents
As discussed in the journal above, Zyklon B leaves behind a distinctive Prussian blue residue on exposure. As you can see in pic related, the Prussian blue residue is clearly present in the Majdanek fumigation chambers, but not in the Auschwitz main homicidal gas chamber.
