Non-aspirating use of AFFF’s has been with us since 1978 or even earlier. This provides us with a large body of peer reviewed data and actual fire fighting experience.
The references below provide some idea of the testing that was carried out. There is also large scale tank fire fighting experience including extinguishing the world’s largest tank fire that was achieved using non-aspirated application of AR-AFFF.
The ability of AFFF to achieve aspiration rates >4:1 traveling through the air is at least in part due to the relatively short carbon chain (8) of the fluorinated surfactants. Some AFFF & AR-AFFF formulations also used shorter chain hydrocarbon surfactants. This is important as the energy required to expand foams that use short chain surfactants is considerably lower than for long chain surfactants. Protein based foams on the other hand do not expand through the air as they require a much higher energy to achieve expansion, even fluoroprotein foams do not aspirate when discharged from fog nozzles. FFFP’s were the first protein based foams that could be used through non-aspirated nozzles as they used the same fluorinated surfactants as AFFF. In a way, the ability to be used through non-aspirated nozzles is an accidental by-product of the fluorinated surfactant content of AFFFs and FFFP’s.
Compared with this we know very little about using F3 foams in this application. They are certainly able to be used (with revised techniques) on spill fires from handlines. One method involves discharging the foam into the ground before the fire, building up a large foam blanket and then rolling the foam blanket over the fire. Clearly, this avoids issues with fuel pick-up and the ability to foam in non-aspirated equipment. However, it is probably not possible to translate this technique to monitors and automated systems such as helidecks and hangars.
The use of short chain surfactants in the F3 formulations will likely be necessary if non-aspirated application is to work. The challenge for F3 foams will be for them to work in more forceful applications such as from monitors.
Two F3 foams have been able pass UL Listing through standard sprinklers. While this is quite a big achievement for an F3 foam, it isn’t the same as non-aspirated application from a monitor. The application from a sprinkler is relatively gentle. The terminal velocity of foam from a sprinkler is likely to be a few meters per second at most, where monitor application velocities may be more than 20 times higher. This would make a big difference to the fuel pick up rate and challenge F3 foams. Extrapolating from non-aspirated sprinkler testing to non-aspirated monitor applications wouldn’t appear to be justifiable.
The main issues are:-
It should be noted that there are no UL or FM approval processes that we know of for non-aspirated foams, the practice arose from the extensive large scale testing carried out in the late 1970’s and 1980’s. It was in quite common use by the early 1990’s. The LASTFIRE project has attempted to produce a small scale test for this application but it would seem to me to be unwise to generalise this to F3 foams without large scale testing as verification.
As a general comment, it seems that large scale fire testing of AFFF’s preceded any approval fire testing. It would seem to be very risky to extrapolate from small scale fire testing to large scale application without any verification at larger scales. There doesn’t seem to be any engineering justification for making such a leap.
If any foam concentrate manufacturer has witnessed test data for this application we would be pleased to be able to publish it here along with their recommendations for application rates.
Bowen, J. E., “To Aspirate or Not to Aspirate AFFF Tests, Advice Helps Answer Questions,” Fire Engineering (February 1981).
Pignato, J. A. “Enhancement of Fire Protection with Directional Cooling Spray Nozzles by Use of AFFF, Fire Technology, Vol. 19, No. 1 (February 1983), p. 5.
Aspirating vs. non-aspirating nozzles for making fire fighting foams — Evaluation of a non-aspirating nozzle DiMaio, L.R., Lange, R.F. & Cone, F.J. Fire Technology (1984) 20: 5.