Compatibility Requirements
The ability to mix Class B foams from different manufacturers has been an issue ever since their introduction. As manufacturers enter or leave the marketplace, the question of compatibility becomes even more urgent. The National Fire Protection Association (NFPA) historically has not permitted the mixing of different brands or types of AFFF or Alcohol Resistant (AR) – AFFF in long-term storage because they may prove to be incompatible. This ruling changed in May of 2002 when the following verbiage was adopted in NFPA 11: Standard for Low-Expansion Foam:

NFPA 11, 2.4.1 COMPATIBLITY OF FOAM CONCENTRATES

"Different types of foam concentrates shall not be mixed for storage. Different brands of the same type concentrate shall not be mixed unless data are provided by the manufacturer and accepted by the Authority Having Jurisdiction (AHJ) to prove that they are compatible. Foams generated separately from Protein, Fluoroprotein, FFFP and AFFF concentrates shall be permitted to be applied to a fire in sequence or simultaneously."

Military/Government Specifications
The testing for compatibility of AFFF agents for the U.S. Military has historically been guided by United States Federal Government Specifications. The Mil-Spec tests, as they are known in the industry, have proven to be excellent indicators of the compatibility of AFFF agents. The current Military Specification that guides this testing is MIL-F24385F. This specification reads in part:

"Compatibility. The concentrates of one manufacturer shall be compatible in all proportions with the concentrates furnished by other manufacturers listed on the Qualified Products List."

The Mil-Spec requires that the AFFF agents meet, among other tests, the following compatibility tests...

All 3% and 6% AFFF agents that qualify under the Mil-Spec can be mixed together in long-term storage without fear of compatibility problems. The Mil-Spec does not cover 1% agents, AFFF that is freeze protected regardless of the concentration, alcohol-resistant agents, Class A foam concentrates, or other types of firefighting agents such as emulsifiers and wetting agents. Anyone desiring to purchase Mil-Spec AFFF should be sure that the product is on the U.S. Military’s Qualified Products List (QPL). There have been instances where foam manufacturers have stated that their products "meet the Mil-Spec requirements" but the product is not on the QPL.

ANSULITE^® 3% (AFC-5A) and ANSULITE^® 6% (AFC-5) AFFF products are listed on the QPL having been successfully tested by the Naval Research Laboratories and found to meet all the requirements of the Mil-Spec.

Alcohol-Resistant (AR) AFFF Agents
With the change to NFPA 11 allowing the mixing of Class B foams, it has now become possible to mix AR-AFFF agents in long-term storage and still conform with the mandates set forth in the NFPA guidelines. Since the use of AR-AFFF is increasing, it is important to understand the difference between AFFF and AR-AFFF. The base material of AR-AFFF is that of a regular AFFF concentrate to which a high molecular weight polysaccharide (a type of sugar) has been added. The reason for the addition of the polysaccharide is to allow the AR-AFFF to form a blanket of foam on (water miscible) polar solvents thus facilitating fire extinguishment by allowing the foam blanket to build up on the polar fuel. If this did not occur, the polar solvent would dissolve the foam blanket. Due to the addition of this polysaccharide and the methods used to manufacture the products, the chemistry of the AR-AFFF products can vary from manufacturer to manufacturer. This manifests itself in several ways through variations in viscosity, color, refractive index, foam expansion, drain time and fire extinguishing performance (the density of the product necessary to extinguish the fire). Currently there are no known products that are identical in all the performance aspects that could be mixed without any testing to assure their compatibility. For this reason, it is very important to ensure that the products you are mixing have been found to be compatible by a reputable laboratory using valid testing procedures. Make sure the report showing this compatibility is verified in writing and signed by an individual who is authorized to represent the manufacturer.

It is important to understand the roles played by Underwriters Laboratories and Factory Mutual concerning mixing foams in storage. Because of the nature of the apprsoval testing done by each agency, any mixing of foam agents in storage will void the UL listing or FM approval. Often, UL listings or FM approvals are essential to the fire protection systems such as when required by an insurance carrier. If UL listings or FM approvals are not required and approval to mix the agents has been received by a qualified testing laboratory, the agents may be mixed in storage.

Also, because of the potential difference in viscosity, some of the agents may not readily mix together. This layering should not cause any problem with the agent’s compatibility. However, it is absolutely essential to remember that in many systems, such as a sprinkler system, the device that proportions the agent is designed to work using an agent of specific viscosity. Changing the agent could either increase or decrease the viscosity. Such a change will have an effect on the proportioning device causing it to potentially proportion too rich or too lean. In any event, the resulting foam/water mixture will not be what the system was designed to proportion and may have an effect on fire extinguishment.

Testing conducted at the agents laboratory of the ANSUL^® Fire Technology Center has indicated that ANSULITE^® 3x6 ARC (Alcohol-Resistant Concentrate) is compatible with National Foam’s UNIVERSAL brand and 3M’s ATC brand. Additional ANSULITE^® ARC’s have also been tested for compatibility.