When and how to use fire grenades

In confined spaces, these mini extinguishers can save lives and property

It is tempting to dismiss thoughts of fire grenades based on our experiences with carbon tetrachloride bombs. But, as we're told to use the technology that works, it is worth revisiting these devices.

Before rushing headlong into what's on today's market, it behooves us to understand where these products came from and how they evolved.

The earliest fire grenades were hand-blown, colored round glass bottles usually filled with salt water. These were designed to be thrown at a fire so the thin glass container would shatter and disperse the water to extinguish the flames.

After 1900, a newer and more industrial looking glass bulb came into vogue. Instead of water, these grenades contained a blue- or reddish-colored liquid, carbon tetrachloride, also known as tetrachloromethane.

This technology was used in conjunction with a bracket assembly that could be mounted on walls or ceilings above high fire-risk areas such as boilers or furnaces.

Much like today's fire sprinklers with their fusible link, when high temperatures reached the device, the bracket would release the globe causing it to crash on the floor and release the carbon tet. 

Some models were more sophisticated and used a heat-activated, spring-loaded trigger to break a bottom seal on the glass vessel to release the liquid at which point a deflector would distribute the carbon tet over a wider area. That's pretty ingenious, especially for the early 1900s, right?

There was just one small problem. While the carbon tet will extinguish the fire, when it's exposed to the fire's heat it can produce a nasty phosgene gas. During the 1940s, scientists also learned that carbon tetrachloride was a probable carcinogen.

A rose by any other name
Today, most of the manufacturers refer to their products as a "fire suppression generator." But I’m pretty sure that the term fire grenade is still catchy, especially with firefighters.

Call them what you will, modern fire grenades do not explode like a grenade. The unit remains fully intact and sends out an aerosol mist at a typically discharge time of about 20 seconds.

This newer generation of fire grenade is touted as having the ability to provide quick fire suppression, especially for fires in enclosed spaces. Here are a few of the features of today's grenades.

  • Zero ozone depletion potential, meaning they don't contribute to global warming.
  • Included in the Environmental Protection Agency's new Significant New Alternatives Policy program as acceptable substitutes for Halon 1301 as a total flooding agent.
  • Extinguishing capability three times that of Halon 1301.
  • No oxygen depletion; they suppress at very low concentrations by interfering with the fire's free radicals, making the atmosphere safer for firefighters and any trapped occupants.
  • Reduces interior temperature in the space quickly, providing increased victim survivability and less heat stress for firefighters.
  • Units are compact, and easily portable to point of attack making them a reliable, cost-effective fire protection tool for a wide range of fire scenarios.

How they work
Most of the grenades operate the same way. In the event of a fire, the first responder activates the unit by removing the safety clip and pulling the ring pin — just like with a fire extinguisher. This initiates a combustion process. The unit can then be thrown into an enclosed space — even up or down a set of steps — to get it close to the fire. As with playing horseshoes, close counts.

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After a delay of less than 10 seconds, the fire grenade's combustion process will have reached a sufficient temperature that begins burning the enclosed stable combustible solid, potassium, producing a fire suppressing aerosol mist. This mist does not reduce the oxygen levels and the fire is extinguished because those ultra-fine particles in the mist interfere with the flame's free radicals. The agent will continue to hang in suspension after delivery providing ongoing suppression capabilities.

A grenade's coverage depends on the characteristics of the situation. Some of the factors at play are the class of fire, level of involvement and areas of potential leakage. 

Tests for units of approximately 1.5 pounds have shown significant suppression effects in a 8- x 10- x 10-foot room — around 800 cubic feet. More units would be required for a larger volume or spaces with excessive leakage.

The aerosol flows and spreads rapidly throughout the space, in a manner similar to a gas. However, since the aerosol is buoyant, more may be required in a high-ceiling situation. The unit is most effective when thrown directly at or near the fire.

Any downsides?
As we learned with fog streams, fire grenades work best on fires in enclosed spaces. That's because the confinement keeps the aerosol mist from dissipating so that it can keep "mixing it up" with those free radicals.

Other than that, I couldn't find anything to make a case against the use of these new fire suppression units. In fact, as demand for the product increases, and prices drop (one manufacturer sells the product in cases of four units for $600 per case), I foresee the fire grenade becoming a cost-effective alternative to fire extinguishers for these reasons:

  • Zero maintenance requirements.
  • Doesn't require the user to get into close proximity of the fire.
  • Less user training is required.
  • Rapidly cools the atmosphere in the room so there's less potential for damage to furnishings and equipment.

I don't know about you, but I'm all in for anything that helps firefighters do their jobs more safely, effectively and efficiently. Let's not forget Life Safety Initiative 8: Utilize available technology wherever it can produce higher levels of health and safety.

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