The sign on the reinforced door read “Projectile Testing” and the crowd gathered in the corridor outside had been warned to expect a small explosion. But when the hoverboard battery blew up with an almighty bang and a flash of yellow flame, Barbara Guthrie flinched all the same.

“Huh!” UL’s chief public safety officer said with a nervous laugh. “Would you say that’s something you want in your home?”

It’s a question parents and other consumers have been asking themselves as reports of spontaneously combusting two-wheeled hoverboards have multiplied in the weeks since the self-balancing electric scooters became Christmas’ must-have toy.

Now — with lawsuits proliferating, the devices yanked from the shelves of Toys ‘R’ Us and other retailers and banned as a fire hazard by major airlines, some college campuses and rail lines — safety-certification company UL, based in suburban Chicago, said it has developed a set of standards to ensure safety.

Last month, the Consumer Product Safety Commission warned that it could impound or recall uncertified hoverboards. UL is one of the places manufacturers can get their products certified.

Founded in 1894, UL provides product safety testing and certification, with its approval mark appearing on 22 billion products worldwide each year. Its labs are a kind of torture chamber for products, the kind of place whose awesome destructive possibilities might appeal to little boys. Products can be pummeled with weights, zapped with electricity or fired upon by an AK-47 assault rifle before they are certified.

Guthrie said most users will not abuse their hoverboards to the extreme that UL does. However, even the most extreme tests reveal flaws in the battery’s manufacturing.

While none of the technology in hoverboards is in itself new, the combination of technologies is, said John Drengenberg, UL’s consumer safety director. Some hoverboards have false UL certification stickers on them. No hoverboard has yet passed the test.