HYDROGEN GAS IS EXPLOSIVE

Sometimes I read something that just catches my attention. A billboard with a controversial slogan, the ingredients of most canned variety of soups, whatever, something grabs my attention and sometimes I learn something new. In this case I was reading a "Quick Start Guide" for a frontload clothes washer. And I got this part:

Under certain conditions, hydrogen gas may be produced in a hot water system that has not been used for two weeks or more. HYDROGEN GAS IS EXPLOSIVE. If the hot water system has not been used for such a period, before using a washing machine or combination washer-dryer, turn on all hot water faucets and let the water flow from each for several minutes. This will release any accumulated hydrogen gas. THE GAS IS FLAMMABLE. DO NOT SMOKE OR USE AN OPEN FLAME DURING THIS TIME.

Who knew doing laundry could be so hazardous?

Of course, that kind of thing isn't a danger in my house, where it's an exception that the clothes washer isn't in operation.

It's also one of those warnings that I'd like someone to independently verify. How easy it to cause an explosion in such a way? How does the hydrogen build-up in the first place? Common thought is that warnings that appear on products are there because some moron without two IQ points to rub together used the product incorrectly. That's why so see those, "This bag is not a toy" and "Poison DO NOT EAT" on those little silicon packets found with new shoes. My imagination takes me to that moment when some repair guy showed to look at a busted washer only to have the whole thing explode in his face when he lit a cigarette. It's straight out of a Daffy Duck adventure.