In Japan it is known as detergent suicide, a near-instant death achieved by mixing common household chemicals into a poisonous cloud of gas.

By some counts, more than 2,000 people there have taken their own lives, inhaling the gas — in most cases hydrogen sulfide — in cars, closets or other enclosed spaces. The police now say they are seeing an increasing number of similar suicides in the United States, inspired by Web sites that carry recipes for the chemical mix as well as detailed instructions on how to use it.

And as in Japan, where the suicides have caused whole neighborhoods to be evacuated and sent dozens of people to the hospital, the desperate and despondent are not the only victims.

Of 72 chemical suicides experts have documented in the United States since 2008, at least 80 percent have resulted in injuries to police officers, firefighters, emergency workers or civilians exposed to the gas, despite the efforts of suicide victims to protect others by putting warning signs on car windows or closet doors, said Deputy Chief Jacob Oreshan of the New York State Office of Fire Prevention and Control, who has been tracking the cases.