Because of the environmental and toxicity issues associated with firefighting foam containing per- and poly-fluoroalkyl substances (PFAS), many firefighting professionals are contemplating changing to a PFAS-free foam (SFFF) as manufacturers have introduced these types of foams to the market. Here are some things to consider before making the switch.
FILM FORMATION
PFAS are added to formulations to enable the foam to form an aqueous film on, and more readily flow across, a flammable liquid. The film prevents evaporation of the flammable liquid and significantly aids in extinguishment of a fire and securement of a spill. This occurs due to the unique properties of PFAS at lowering the surface and interfacial tension of the foam solution. Depending on the hazard, PFAS-free foams available today may not have this film-forming capability and would then rely solely on the foam bubble for extinguishment and securement. Consequently, there may be scenarios where PFAS-free foams do not perform as effectively as foams containing PFAS.
EQUIPMENT
To ensure the best performance with a PFAS-free foam, make sure that it is listed or approved by an independent testing organization. These test organizations approve the foam in combination with proportioning and application equipment. Only use the foam with the listed equipment. Because PFAS-free foams may rely strictly on the foam blanket for extinguishment, the correct foam expansion ratio is critical to performance. The application device, at the correct inlet pressure, will provide the expansion ratio that was used to extinguish the test fires.
EXPANSION RATIO
A good source of information is the NFPA 11 Standard for Low-, Medium-, and High-Expansion Foam Annex H – Synthetic Fluorine-Free Foam (SFFF) Research Testing Summary. This annex states the following in reference to expansion ratio and PFAS-free foams.
“SFFFs presently available appear to work much better on extinguishing Class-B fires when applied using an air-aspirated nozzle, whether fixed equipment, handline, or master stream. This results in an air aspiration ration of at least 7 to 10 times foam solution to air aspiration.”
AFFFs are often applied with non-air aspirated nozzle because they perform well at a low expansion ratio, even as low as 4 to 1. The non-air-aspirated nozzle generates foam that provides longer reach and wind resistance, permitting the firefighter to apply foam from a safer distance.
PFAS-CONTAINING FOAM DISPOSAL
When removing PFAS-containing foam from a system, it will need to be properly disposed of. There is currently some controversy on the best way to dispose of PFAS-containing foams. A few years ago, incineration was recommended. But there are concerns that incomplete incineration may result in releasing PFAS into the environment. It is advisable to check with the local authority for the recommended disposal method.
SYSTEM CLEANING
Once the PFAS foam is removed from a system, the system should be cleaned prior to filling with a PFAS-free foams. Typically, several rinses may be required, and the rinse water (or other rinse substance) will need proper disposal, like the PFAS-containing foam. It is unlikely that the system can be cleaned to the degree that no PFAS can be detected in the rinse because todays analytical techniques can detect PFAS at levels of 10 part per trillion and even less. However, it is best to check with the local authority to determine the appropriate level of PFAS in a cleaned system and it may be necessary to test the PFAS level in the rinse water prior to filling
COST
The cost of changing out a system may include:
- PFAS-free foam
- Equipment modifications
- Discharge devices
- Tanks – if increased application density is required.
- Proportioning – some of the PFAS-free foams are very viscous and may require a larger proportioning orifice or a different proportioning system. Check the listings or approval.
- PFAS-containing foam disposal
- Rinse water (or other rinse material) testing and disposal
- System testing
- Other costs – such as engineering, labor, etc.
ACCEPTANCE TESTING
Prior to putting the new foam into service, typically foam flow tests are recommended to verify the foam is proportioning at the specified concentration.
NFPA 11 Section 12.9.4.1.4 "The foam concentrate induction rate of a proportioner, expressed as a percentage of the foam solution flow (water plus foam concentrate), shall be within minus 0 percent to plus 30 percent of the manufacturer’s listed concentration, or plus 1 percentage point, whichever is less."
Acceptable Concentration During Flow Testing
| Nominal Foam Concentrate (%) | Minimum % During Flow Test | Maximum % During Flow Test |
|
1 |
1.0 |
1.3 |
|
3 |
3.0 |
3.9 |
|
6 |
6.0 |
7.0 |
Even though the system will contain PFAS-free foams, check with local authorities to determine the proper commissioning and disposal of foam solutions discharged during testing.
ANNUAL TESTING
As with PFAS foam, it is recommended PFAS-free foam be tested annually by a laboratory. Verifying the expansion level and 25% drain time will be vital to ensuring continued performance.
NFPA 11 – 13.3.4.2 “Foam Concentrate Samples. Samples of foam concentrates shall be sent to the manufacturer or qualified laboratory for quality condition testing at the frequency recommended by the manufacturer.”
Comparison of PFAS-Containing and PFAS-Free Firefighting Foams
| Property |
PFAS-Containing |
PFAS-Free |
|
PFAS Concentration |
Typically, 10,000-0,000 ppm |
Less Than 1 ppm |
|
Film Formation |
On many flammable liquids
|
No |
|
Optimum Expansion (Typical) |
4:1 to 6:1
|
Greater than 7:1 |
|
Compatible with Non-Air Aspirated Application Device
|
Yes
|
No |
|
Environmental and Toxicity Concern |
Yes |
Check the product
|
|
Nozzle Reach |
Longer due to low expansion |
Shorter due to higher expansion |
If you have any questions regarding this article, please contact Dyne Fire Protection Labs at joan@dyneusa.com or 651-230-1177.
©Dyne Fire Protection Labs 2023