“Drying things out”
Over the last 2 parts of this series, we have looked at water and foam extinguishing agents. Before moving on to Gel
Products (in the final segment) we have to take a look at another major player in the Fire Suppression
arena: Dry Chemicals.
While chemical agents have been in use since the 1800’s, Dry Chemical agents didn’t truly take hold until the 1900’s. It is not hard at all to find an ABC extinguisher in close proximity to you, at nearly any time. We have them in our homes, automobiles, public buildings, industrial complexes and yes, even on our apparatus.
Dry Chemical agents have definitely become a mainstay in the public and the Fire Service. This is due to several factors.
1. The works very well for small (incipient/ignition stage) fires.
2. When used in proper quantity and application, by a trained individual, they work extremely well on flammable liquid fires (both large and small).
3. Most agents are compatible to use simultaneously with straight water or foam, without destroying the foam product.
4. Since they are mostly employed in small, handheld extinguishers, it is easy to teach a layperson how to operate and be effective at stopping small fires from growing out of control, in very little time.
A couple drawbacks of Dry Agents is that they can be quite corrosive if left on metal or painted surfaces, do not play well with electronics and they are MESSY and hard to clean up. Once an agent has been discharged into a convection column, of any size, the light powder product is invariably carried into areas that were nowhere near the fire. It is not uncommon for Firefighters to arrive the scene of a kitchen fire to find everything completely covered with a thin coat of yellow/green powder, no fire, and a homeowner saying, “okay, I put out the fire, now how do I clean up this mess?”.
Dry Chemical agents contain properties that make them impervious to water. They float quite nicely! This characteristic makes them both naughty AND nice, at the same time. This property allows the Firefighter that ability to operate Dry Agents in conjunction with water (utilizing a water stream to carry the agent to a fire that an extinguisher would not ordinarily be able to reach on its own). It also makes for a bit of a clean-up nightmare. Since it doesn’t “cling” to water like dust or other powders, it does not “wipe” up well with a wet cloth. You can wash it away but….only to find that it has puddled nicely in some corner (not to mention, it is probably not a brilliant idea to “wash” down your kitchen with a garden hose. That would be a mess all its own.)
Monoammonium Phosphate is the most common dry chemical agent on the market. It is sold in general stores and can be found in most businesses, offices, and even homes. It is pale yellow in color and is used for A, B, and C class fires. It is classified as a “multi-purpose” agent. Its major disadvantage is that is the most corrosive of the dry chemicals and does make quite a mess when utilized in an enclosed space. Its primary action is the “coat” the burning product, thus extinguishing the fire.
Sodium bicarbonate was the first of the dry chemicals and was developed to interrupt the chemical chain reaction in Class B and C fires. It is not seen quite as often now, as it has given way to more effective agents such as Potassium Bicarbonate.
Potassium Bicarbonate or “purple K” is one of my favorite agents. It is extremely useful on flammable liquid fires and is heavily utilized by the military and the auto racing industry. Purple K is also often found in large wheeled units next to airport hangers and taxi-ways. A major advantage of PK is the fact that it is very compatible with AFFF and is the only agent certified by the NFPA for that utilization. While fuel-oil and chemical companies prefer PK for its ability to rapidly handle class B fires, the racing industry (i.e.-NASCAR) utilizes PK for both its Class B properties and the advantage of fighting fires on highly-heated engine and brake parts without cracking the metal (as would happen if water/foam were applied).
Over the years, Sodium Bicarbonate, which was once a preferred agent for kitchen fires has gone by the wayside in favor of other K-class agents, however, PK and Monoammonium Phosphate have remained in heavy use.
While the intent of this article is not to describe all of the various “dry chemical” agents or to give a complete history of such, it is the intent to put together a broader view of fire-suppression agents for the reader. Dry chemical agents are not going away anytime soon. They are effective means of fire control and affordable fire protection for the average citizen. There are definitely times when the fire service should utilize them and they should not be overlooked.
Thus far, we have discussed water, foam and dry chemicals. Now that we all have had a brief refresher on the basic tools of fire suppression, we have used for over a century, our next venture will be into the future of fire suppression. Now that we understand where we have been and how we got to where we are to date, it’s time to look at the technology that will shape fire suppression in the future (and is doing so even today).
Till next time…..be safe out there!