Sugar Creek, Mo. ? Four emergency responders and a relative of a man who used hydrogen cyanide to kill himself in his truck were hospitalized after being exposed to the gas, police said.

A firefighter, three police officers and the man’s sister-in-law tried to make contact with the man, who was found unresponsive in his truck on Monday with two gas canisters on the floorboard. The man, who was in his late 50s or early 60s, left a suicide note on his computer screen saying that he had used cyanide gas to kill himself, police said.

“It’s extremely dangerous,” Sugar Creek Police Chief Herb Soule said. “In this case it was fatal, but it’s also dangerous to the rescue workers and we’re in the process around the country of sharing information on this.”

Soule said the police department in the community just east of Kansas City received a bulletin two weeks ago warning law enforcement agencies to be aware of such chemically induced suicides after two cases in New York and dozens in Japan.

The five people who were exposed to the gas in Sugar Creek were out of the hospital by Tuesday afternoon.

“The first firefighter on the scene, of course, went to check for signs of life,” Soule said. “He had to open the truck door so he was exposed to the fumes.”

Investigators are trying to determine how the man got hold of the hydrogen cyanide, which is similar to that used in Holocaust-era gas chambers.