25. June 2012 06:10
(A segmented look at Firefighting, Fire Extinguishing Products, and Fire Suppression)
In this segment we’ll look at fire extinguishing products and their effectiveness.
It appears that wildfires have become a pandemic and we have all seen the news clips of airplanes and helicopters dropping some sort of liquid on a fire…
But what is that liquid?
Some of it may be clear, some of it appears to be bubbly, and some of it may be red or blue. More often than not they are fire extinguishing products and some have been around for close to 100 years to aid firefighting efforts and help to firefighters with fire suppression. So let’s look at these fire extinguishing products and how well do they work for fire suppression.
Firefighting foams are the chemicals that have been around longest ever since the early 1900’s and developed by a Russian Chemist named Alexsandr Loran. Originally firefighting foams were designed to combat flammable or combustible liquid fires. It wasn’t until the 1980’s when the foam manufacturers came up with the idea of making a formulation to be used on wildland fires which has evolved into Class “A” foam.
So what are firefighting foams or class “A” foams?
The chemical composition of these fire extinguishing products vary from manufacturer to manufacturer but all contain some sort of surfactant. Surfactants are compounds that lower the surface tension of liquid (usually water). Surfactants are usually organic compounds which are carbon-containing compounds such as carbides, carbonates, simple oxides of carbon and cyanides. Other components of firefighting foams are organic solvents such as trimethyltrimethylene glycol and hexylene glycol, foam stabilizers such as lauryl alcohol, and corrosion inhibitors.
Now that we have your attention of what’s in firefighting foams! Let’s look at their effects on the environment…
The US Forest Service QPL (Qualified Products List) specifies a mix ratio of 0.1 to 1.0 % foam concentrate to water and clearly states that they must be mixed within that ratio to comply with their specifications. Now on the other hand firefighters are taught in the Fire Academy to mix firefighting foam at a ratio of 3 gallons of foam concentrate mixed with 97 gallons of water to get an end product of 3% foam. Hmmm the US forest Service says a maximum of 1%... Why?? Let’s look at toxicity on mammals and fish…
Acute Oral Toxicity Mammals (Foam Concentrate):
Phos Chek WD 881 = 4378 LD₅₀ (mg/Kg) it also is moderately irritating to non washed and washed eyes, and has a 0.9 primary irritation index for skin irritation.
Phos Chek WD 881-C = >5050 LD₅₀ (mg/Kg) it is also moderately irritating to non washed and washed eyes and has a 1.4 primary irritation index for skin irritation.
Tyco Silv-Ex = >5050 LD₅₀ (mg/Kg) it is also severely irritating to non washed and washed eyes and has a 2.7 primary irritation index for skin irritation.
National Foam KnockDown = >5000 LD₅₀ (mg/Kg) it is also moderately irritating to non washed eyes and mildly irritating to washed eyes and has a 1.2 primary irritation index for skin irritation.
**Note** The lower the Lethal Dosage value (LD₅₀) is - the more toxic it is.
Fish Toxicity (Foam Concentrate):
Phos Chek WD 881 = LC₅₀ 11 mg/L soft water and 10 mg/L hard water.
Phos Chek WD 881-C = LC₅₀ 17mg/L soft water and 10mg/L hard water.
Tyco Silv-Ex = LC₅₀ 46mg/L soft water and 28mg/L hard water.
National Foam KnockDown = 28mg/L soft water and 26mg/L hard water.
**Note** The lower the Lethal Concentration value (LC₅₀) is - the more toxic it is.
Let’s look at what firefighting foams do to fire equipment? We already established that firefighting foams contain corrosion inhibitors. Corrosion inhibitors are a chemical compound that decreases the corrosion rates of a material, typically a metal or an alloy. Corrosion tests are designed to measure the loss of structural integrity of the affected metal and potential loss of the metal item. Significant corrosion in fire pumps or aircraft may have catastrophic effects to human life. Corrosion testing is based on mils-per- year and the US Forest Service is looking to minimize the risk of corrosion- caused fire equipment failure in the field. The benchmark is less than (Uniform Corrosion Partial Submersion at 120˚F (Foam Concentrate):
Phos Chek WD 881 = 0.1 Aluminum, 1.9 Steel, and 0.5 Yellow Brass.
Phos Chek WD 881-C = 0.9 Aluminum, 4.7 Steel, and 0.7 Yellow Brass
Tyco Silv-Ex = 0.1 Aluminum, 4.9 Steel, and 3.5 Yellow Brass
National Foam KnockDown = 0.4 Aluminum, 1.1 Steel, and 0.1 Yellow Brass
While all of these firefighting foams comply with the US Forest Service Specifications it should be noted that the above testing results is public record and are published on the US Forest Service’s website.
How effective are firefighting foams in aiding firefighters in fire suppression or fire extinguishment?
Simply it last for seconds compared to water!!
Here are the test results from the US Forest Service QPL list.
Lateral Ignition Flamespread Test (LIFT)
Phos Chek WD 881 = 211 seconds compared to Water = 112 seconds
Phos Chek WD 881-C = 255 seconds compared to Water = 124 seconds
Tyco Silv-Ex = 139 seconds compared to Water = 128 seconds
National Foam KnockDown = 225 seconds compared to Water = 116 seconds
Basically what we have learned from this segment is that firefighting foam is corrosive to firefighting equipment, it’s not that great for the environment, and it’s not very effective compared to water.
So stop wasting the taxpayer’s money!
On a side note National Foam as well as AFG Firewall, Kidde, and Ansul are all owned by Tyco. In the next segment we will look at Long Term Retardants the red stuff being dumped from airplanes and helicopters…
By: Rob Rosovich, Fire Protection Engineer