Hydrogen sulfide gas has a density higher than air. It inhibits mitochondrial enzymes by binding with ferric ion of cytochrome oxidase. This blocks the use of oxygen within cells.
Method: 2 common agents are mixed. One contains a strong acid (usually hydrochloric acid) and the second contains a sulfide source.
Examples of an acid source: toilet bowl cleaner, tile or stone cleaner, surface decontaminant
Examples of sulfide or sulfur source: fungicides, pesticides, paints, dandruff shampoo, sulfur-containing bath salts
The person usually is alone and in an enclosed space, often an automobile.
The hydrogen sulfide is a hazard for first responders if the location is completely closed. A "rotten egg" odor can be an important indicator of the hazard. Some victims are courteous enough to leave a note on the outside of the space warning of the danger.
Postmortem findings:
(1) hemorrhagic pulmonary edema
(2) scattered petechiae
(3) myocarditis
(4) greenish coloration to organs
Laboratory findings:
(1) blood thiosulfate levels are elevated
(2) tissue thiosulfate levels may be elevated in lung and brain
(3) elevated methemoglobin
