Class A foam: Q & A
by
Dominic J. Colletti
Although the new generation of Class A foams were originally developed for
forestry firefighting in the mid-1980s, practical experience and testing has
shown that it can be a valuable tool to manually combat other Class A type
fuels, including structure fires. New foam application equipment has reduced the
logistical requirements burdened on the pump operator to efficiently supply
Class A foam on the fireground. This has made its use feasible for municipal
fire operations. What follows are some frequently asked questions about this
technology.
Why is
Class A foam more effective than plain water on Class A type fires?
Plain water has inherent limitations in cooling and penetrating Class A
fuels because of a naturally high surface tension. This high surface tension
causes water to form into droplets, and consequently, the majority of the
droplets roll off fuels, impeding water's heat absorption potential.
Class A foam concentrate treated water (foam solution) has reduced surface
tension and allows more surface area of water droplets applied to contact the
ordinary combustible surface. This provides increased heat transfer through
conduction.
Class A foam concentrate is technically known as a synthetic detergent
hydrocarbon surfactant, and when mixed with water at the recommended ratios, is
biodegradable. Because it is a hydrocarbon surfactant, it also has an affinity
for carbons and causes the water (as foam solution) to penetrate into wood
fuels.
Class A foam solution can be aspirated (entrained with air) by application
through a fog or air aspirating nozzle, or a Compressed Air Foam System (CAFS).
Different quality finished foam blankets can be formed using these foam
generation devices. Forming a low expansion, quick draining finished foam bubble
blanket will yield additional fire suppression proficiency upon direct attack by
enabling the foam solution to adhere to horizontal and vertical three
dimensional fuels. Foam bubbles adhering to fuels will cause the foam solution
to remain on it where it will penetrate or evaporate, until it is all gone. The
net effect of using Class A foam in this fashion is that the available water
supply is efficiently used to cling to and cool the fuel. This maximizes water's
ability to suppress the fire, rather than being wasted by running off of it.
How can
Class A foam help our daily fire operations?
The major percentage of working alarms that municipal departments respond to
are Class A fires. From that standpoint, methodologies that increase fire
suppression capabilities should be closely investigated because of the potential
benefit to the total number of incidents. In simple terms, using Class A foam
correctly can provide a tool to increase the effective application of water on
these hazards. The benefits of adopting Class A foam may include increased
firefighter safety, increased fire operation efficiency and reduced property
damage. In most scenarios, using water more efficiently will mean reduced
knockdown and total extinguishment time, and as a prime effect, firefighter
stress from exposure to heat and toxic products of combustion will be lessened.
Rural departments depending on a labor and equipment intensive water supply
can extend the capability of water shuttle operations. Because of faster fire
control, less total water may be needed for extinguishment when using Class A
foam. This can help reduce total fire and water damage, and thus the
environmental and financial impact of fire on the community.
Can the
benefits justify the cost?
From a cost standpoint, Class A foam concentrate is generally proportioned
at 3/10 to 5/10 of 1% when used for direct attack. This is only a fraction of
the proportioning ratio typically used with Class B flammable liquid foams
(usually 3% and 6%). This low proportioning ratio, and its ability to make water
a more effective firefighting agent makes usage cost effective. Each individual
department should prepare an analysis of required implementation/operation
costs. These costs should then be weighed against the potential benefits to the
total fire operation and the community. This should be performed after a
thorough review process of Class A foam technology.
Can Class
A foam be utilized for interior structural attack? If so, what are the benefits?
Most municipal departments have hydrated fire districts with good water
supplies. With proper training, Class A foam can be utilized very effectively
for both interior and exterior structure attack. At least one reason why Class A
foam should be used for interior attack, even though a good water supply may be
available, can be better understood through examining plain water application
requirements, such as the Iowa formula, and by looking at actual interior gpm
flows used today. Some have said that water flow formulas developed years
ago are no longer valid today because of the increased interior fire loading
characteristics of home furnishings manufactured from synthetic materials,
whereas all natural fires were ordinarily used years ago when these formulas
were developed. While it is true that these synthetic materials have
considerably increased fuel loading, it is also true that many departments have
replaced 1½" hose and variable gallonage nozzle with 1¾" hose and automatic
nozzle. In as much as this larger hose line and nozzle is capable of delivering
the higher flows primarily found with 2½" diameter hose line, aggressive
interior attacks are only normally delivering 95 to 150 gpm water flow. It is
difficult to realistically use higher interior flows because of high nozzle
reaction force, the inability of the attack team to advance awkward hose line
from the higher pressure required and because there are limited firefighting
personnel found on the responding engine. Realizing that there are practical
limits to interior attack flow rates, adding Class A foam concentrate can be a
justifiable alternative to increase the fire-killing and fuel securing action of
interior fire streams. This may help offset higher interior fire loading found
in most residential occupancies today.
When
talking about Class A foam, the term CAFS is often discussed. Can CAFS be used
by municipal fire departments, and do they offer any advantages?
Compressed Air Foam Systems or CAFS, describes a high energy foam generation
system that utilizes an air compressor to generate the foam bubbles within the
hose line. This system can offer advantages over conventional application
equipment. CAFS are becoming widely recognized as giving quicker flame
knockdowns, increased reach and more finished foam product variability for a
wide range of tactical uses. There are several municipal fire departments using
CAFS for structure attack.
What
equipment is needed to produce Class A foams in municipal fire operations?
Most departments have some experience with Class B flammable liquid foams.
Class B foam concentrates are mixed with water (proportioned) and then aspirated
(air-added) to create finished foam blankets. Class A finished foams are
produced in this way also. The major difference in producing Class A foam is
that lower proportioning ratios are required.
What is
the typical equipment installation for departments that are using Class A foam?
Many are installing variable speed direct injection, discharge side foam
concentrate proportioning systems. These systems offer advantages over common
educators and other methods of integrating foam concentrate with the fire
stream. They are available in 12 volt DC, are small in size and usually mounted
in a storage or pump compartment. These direct injection foam concentrate
proportioning systems allow reliable, easy to control foam production, and keep
foam concentrate out of the fire pump and water tank. They are unaffected by
changes in suction and discharge pressures within their design specifications.
Many apparatus installations include dual foam concentrate tanks, one holding
Class A foam concentrate, and the other holding 1% Aqueous Film Forming Foam
Concentrate. This allows for suppression of Class A type fuels and also normal
hydrocarbon Class B flammable liquid fires.
Conventional smooth bore and automatic nozzles are compatible with Class A
foam. Nozzles can be swapped or attachments added to aspirate the foam solution
and create finished foam blankets of varying degrees for a variety of tactical
uses, such as exposure protection.
Is
training required to place Class A foam agents in fire operations?
Training is essential for the successful implementation of Class A foam into
fire operations. The benefit of any new firefighting concept is directly
proportionate to the knowledge of the user. It is important that the entire
department become involved in the education and training process. This could
begin with the truck committee gathering all the technical information available
on the subject through contacting various manufacturers and users of Class A
foam systems. Training and educational manuals and videos should be purchased
through nationally recognized training agencies. Some equipment and foam agent
distributors are available to demonstrate their wares. Hosting a live fire
demonstration would be an excellent method to introduce the Class A foam concept
to the department and obtain some hands-on use. A qualified instructor that has
experience with Class A foam should be the instructor-in-charge of the foam
portion of the live fire demo.
After the decision has been made to purchase Class A foam equipment, a
systematic training program should be formulated and placed into action upon
system delivery. This should include but not be limited to:
Fire departments looking at Class A foam should realize that when the
technology is used correctly it can present a tangible gain in fireground
operational effectiveness and firefighter safety. However, it is not a "cure
all" for all the problems encountered in fire operations. A successful training
program will result in maximizing its benefits and communicating its limits and
capabilities to fire personnel.
About the author:
Dominic J. Colletti is the foam systems product manager at Hale Fire Pump
Company in Conshohocken, PA. A former volunteer firefighter in New York state,
he is a fire protection system engineer, specializing in foam systems
design/application.