Common Fire Safety Device in Old Homes a Health Hazard

William Kibbel III, The Home Inspector

We have a liquid-filled glass ball hanging over our boiler in the basement. Our heating contractor called it a "fire bomb" that automatically explodes in case of a fire and spreads a chemical to put it out. It seems really old. Would it still be effective?

It's appropriate that your contractor called it a fire bomb as many of these contain a harmful chemical. They can even be deadly during a fire. They were sold through direct marketing and magazine ads from just before 1870 until about 1940. They seemed quite popular in my area as I still find them in around 1 in 15 older homes. Occasionally, I'll see a home with a dozen or more.

The earliest glass fire-suppression devices or "fire grenades" were hand-blown, patterned, often colored round glass bottles, usually filled with salt water until about 1900. These were intended to be thrown at a fire and the thin glass container would shatter and disperse the water to extinguish the flames. With only a very small volume of liquid in the bottles -- about a pint, I can't imagine they were very effective. It's not unusual to come across these early style devices in antique and collectible shops.

After the 19th century, the fancy blown glass began to disappear and a more industrial design prevailed, with smooth, frosted or clear glass. The liquid in the clear glass often had a blue or red coloring agent. In most of the more recent devices, the common type that are usually still around, a fire suppression chemical is likely to be present instead of the salt water. The chemical of choice was carbon tetrachloride a.k.a. tetrachloromethane, which can be really unhealthy if inhaled, ingested or absorbed. Material data safety sheets also show it to be a probable carcinogen. Even worse, when this chemical is exposed to the heat of a fire, it can produce phosgene gas, a chemical weapon used in WWI.

In addition to being able to be thrown at the fire, the more recent fire grenades usually had a bracket assembly that suspended them directly over areas of particular fire risk, like boilers and furnaces. If high temperatures reach some styles of brackets, it would release the grenade that would then crash and shatter, releasing the fire suppression liquid. Others had heat-activated, spring-loaded triggers that would break the bottom seal, spilling the liquid onto a deflector that would distribute it over a larger area. There is one brand that has an aluminum can instead of a glass bottle. This device is under pressure and has a heat-activated sprayer head.

When I find a fire suppression grenade in an old home and it doesn't clearly state that it contains salt water, I'll assume it contains carbon tetrachloride. I advise folks to have it disposed of professionally. Your local municipal environmental officer or fire marshal will probably have specific instructions on how it should be handled and where it can be disposed. I'll be checking to make sure you're not trying to unload it on eBay.

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