Search Past Articles
Explore Past Articles
Haz Mat "Specialist Course"
« Foam 109 - Blended Fuels | Main | Foam 107 - Application Techniques »
Thursday
Oct312013

Foam 108 - Class "A" Wetting Agents

You noticed I refrained from using the “F” word for this material. Herein lays the problem with most fire department operations. Terminology attempts to classify this material as Foam. While it physically may be incorrectly referred to as, operationally, it should never be considered as such. The reason is it becomes acquainted with all our past discussions of Class “B” FOAM. When this happens, confusion on application, mitigation, and various techniques destroy all the hard study you have demonstrated to get to this point!

It is helpful, (and more appropriate) to use the term “Wetting Agent” for class “A” concentrate. This will divide the two substances based on their effective chemistry which is the core of this writing. NFPA-18 defines the standard for wetting agents/class A as;

“A chemical compound which, when added to water in proper quantities, materially reduces surface tension, increases its penetrating and spreading abilities, and may also provide emulsification and foaming characteristics”.

Class A fuels are defined as “woody cellulose materials” in other words organic once grown or “natural” substances. Wetting agents are designed to break down surface tension and “increase the penetrating power of water”. This is opposite chemistry to Class “B” Foam. Herein lays the “key” to understanding why they are rated as different classes by the NFPA. Wetting agents should only be used on class "A" fuels.

Many times potential “clients” may be enticed to purchase new products suitable for both classes of fires and vapor suppression activities. This should be avoided as it is untrue. The proof comes from NFPA 11 and NFPA 18 as evidenced by this development of separate standards within the same technical committee. Wetting agents can momentarily “encapsulate” fuel, but this only contributes to a quick knockdown with “possible” re-ignition protection from a constantly vaporizing hazard. A second “trick” demonstrated by these snake oil salesmen,  is to simply overwhelm a small fire using dilution from a large hand line and wetting agent. This demonstrates the adage; “dilution is not the solution to pollution”. The end result is a magnified volume of hazard, no post-fire security, and no stoppage of vaporization from the hazard surface. The hydrocarbon surfactants used in wetting agents/class “A” are not compatible with class “B” fuels and materials. It is just not physically possible for opposing chemistries to function on the same materials.

Class “A” wetting agents are basically degreasers requiring re-lubrication of valve operating appliances. To avoid issues with apparatus, either add a “flush” cycle to the pump operators SOP’s or better yet avoid internal pumping system contact. If your system must flow the class “A” wetting agent through your apparatus pump, be sure your service maintenance personnel are aware of your practices. Additional preventative service may be required. Your DPS crew can research this from their perspective more thoroughly. This can be accomplished by external devices such as the in-line Eductor. Class “A” wetting agents are available in two (2) basic types;

1] Regular and

2] Cold Water versions.

Regular wetting agents operate at a minimum temperature of 40 degrees Fahrenheit while “Cold” versions operate down to 15 degrees Fahrenheit specifically designed for colder regions of the Northern hemisphere.

Wetting agents in the class “A” world have many benefits;

1] Increase the volume effectiveness of water

2] Reduces suppression mop-up time

3] Simple Eduction

4] Effective on all types of class “A” fires

5] Provide “wild-land” fire barrier when used with a CAFS system

6] Raises moisture content in class “A” materials

7] Absorbs 3X more heat than water alone

Among the class “A” wetting agent concerns are;

1] As with most detergents they are irritating to the skin and eyes

2] By stripping natural oils they are abusive to clothing, footwear, and gloves

3] Degreasers remove lubrication from pump interiors and devices

Class “A” wetting agents have a variety of nozzle choices for a variety of uses. When discharging at a rate of 0.1 to 0.3% for firefighting, standard adjustable fog nozzles will optimize application. When discharged at 0.5 to 1% for mop-up or pretreatment of woody materials a Foam nozzle or CAFS system is a better choice. These nozzles will provide improved expansion and longer lasting foaming ability. Only use CAFS systems for exterior fire attack for firefighter safety.

In finished Foam suppression there is a difference. Class “B” flammable liquid Foam and Class “A” wetting agents are clearly separated by NFPA 11 and NFPA 18 for a reason! This includes testing, certification, materials, use, deployment, and UL testing for certification. Know these differences to prevent incident failure and to secure personnel life safety.

                        Haz Mat Mike

PrintView Printer Friendly Version

EmailEmail Article to Friend

Reader Comments

There are no comments for this journal entry. To create a new comment, use the form below.
Editor Permission Required
You must have editing permission for this entry in order to post comments.