What's All This "Bump" Test Stuff About Anyhow?

True story: On a warm summer morning, the operations crew sat in the control room of a rural western US manufacturing facility. During their morning discussion, one of the operators noticed the smell of gas. The operators called the company safety department, reported the odor and asked that someone come to the control room to investigate. The safety department sent someone up stairs with a typical multi-gas monitor designed to detect carbon monoxide, hydrogen sulfide, oxygen and combustible gases. The monitor was turned on and placed on the control room counter. After a few minutes, the readings on the instrument showed all clear and the operating staff continued about their normal business. A short while later the workers agreed that the odor was getting stronger, despite the lack of any positive indication from the monitor. They decided to evacuate the control room. Evacuation wasn't sufficient for one curious operator however. Wanting to believe that the electronic gas detector was more efficient than his nose, he reached back inside the control room door as he left, pulled the cigarette lighter from his pocket and struck the arc. The ensuing explosion and fire tragically resulted in a number of serious burns and injuries. Fortunately the accident in this case wasn't fatal.