Hydrogen sulfide gas (H2S) has been in the news lately because of its use in suicide attempts. By mixing basic household chemicals together, you can create a cloud of hydrogen sulfide gas that is highly toxic (AKA detergent suicide). This page from the New York State Office of Homeland Security describes the types of chemicals that can combine to create H2S. It also discusses the threat posed by the gas to police and fire personnel who arrive at the scene of a suicide. This video discusses safety procedures around hydrogen sulfide:
In Japan, where hundreds of people per year are committing detergent suicide, the high toxicity of H2S causes officials to evacuate whole buildings when a suicide is discovered.
But there is another side to hydrogen sulfide gas that is less depressing. H2S might be used to create a reflective blanket over the planet to lower earth's temperature. When volcanoes inject large quantities of sulfurous gases into the atmosphere, there is a noticeable cooling effect on the planet. Therefore, the thinking goes, it may be possible for humans to release large quantities of H2S to create the same effect:
Here's how the idea would work: Using planes or other high-altitude transport, we'd disburse millions of tons of sulfur dioxide (or hydrogen sulfide) into the stratosphere, 13 miles above the Earth. Those gases would create tiny particles, which would reflect sunlight.
In small quantities, hydrogen sulfide may even become beneficial to trauma patients:
While high levels of H2S kill mammals, Roth's team has found that very low levels of the toxin can prolong their lives. H2S reduces oxygen levels in the body, and though too much causes death by oxygen starvation, a bit less slows a creature's metabolism. This alone is an amazing finding. But Roth has gone further, inducing suspended animation in mammals. By exposing lab mice to small doses of H2S, Roth and his team can put them into the deepest of sleeps—with very slow, or even no heartbeats—for several hours. In that time, the mice can be cooled to temperatures that would have killed them prior to the H2S exposure.
If scientists can learn how to tap this effect in humans, it would lead to a revolution in anesthesia. See How Anesthesia Works for background.