This webpage is maintained by the Centers for Disease Control and Prevention (CDC). The webpage provides information and resources on Arsine. "Arsine is a colorless, nonirritating toxic gas with a mild garlic odor. The odor can be detected only at levels greater than those necessary to cause poisoning. [...] Arsine is formed when arsenic comes in contact with an acid. [...] Arsine is similar to a gas called stibine, which is formed when the metal antimony comes in contact with an acid. Stibine has health effects similar to those of arsine, but it is not as widely available, and it has a much more noticeable odor (like rotten eggs)."
Centers for Disease Control and Prevention: http://www.cdc.gov/