Immersed in Bubbles
Compressed-air foam systems frequently get a bad rap from mechanics and emergency vehicle technicians, partly because of the systems’ complexity. But rather than look at the system as a whole, instructors at last week’s International Class A Foam and CAFS Academy recommend that technicians look at the three components that make up a CAFS as separate systems.
“[Technicians] need to break it down into the three main components: traditional fire pump, a traditional foam proportioner and an air compressor system,” said Ray Frey, customer service manager with Waterous Arizona, who was one of the instructors for the foam academy’s mechanics’ track. “Most technicians look at the whole system and say it won’t work. We teach them to break the system down and what components are we working on.”
About seven years ago, Frey and Keith Klassen began to develop mechanic-specific classes on foam systems. They found that they couldn’t fit all the information they had to deliver into an 8-hour class and now they insist on 16 hours for a training class in order to really delve into CAFS.
“In years past, maintaining a CAF system would be a problem because of the lack of information and lack of classes on how to maintain the system,” Frey said.
Frey, Klassen and other CAFS instructors teach the basics of CAFS, and then go in depth with the each component of the systems, focusing on the foam proportioner and the air control circuit because, according to Frey, that’s where they see most issues.
“Once we do that, it clarifies the rest for the technician. From there we take them outside to run the system,” Frey said. “We make the system not function and have the students troubleshoot and make the repairs.”
Most CAFS instructors I have met are very objective and eager to dispel myths and rumors about CAFS. In fact, due to the high number of participants in the Glendale foam academy’s mechanic track, Pierce’s Clarence Grady jumped in and helped teach one group of students.
“Rather than teach just our system, we feel we should educate on all systems,” Frey said. “It’s better for the industry and for the fire service. Our goal is to get the information out and let the customers decide which one they like.”
“If technicians don’t know how to repair CAFS, they do the firefighters no good; the technicians should be higher skilled than the firefighters, otherwise how will they know if CAFS is operating or not?”
I’ve been writing about Class A for more than 18 years, and I’ve found that three arguments keep fire departments from embracing foam: lack of training, myths, and cost. I think the benefits of using foam, however, far exceed the arguments, but then again I just spent three days immersed in bubbles.
February 24th, 2010 at 4:16 pm
I wish I would have heard about the International Class A Foam and CAFS Academy so to have attended. Is there a published summary of the Acedemy? I would like to build on my foam training lesson plans.
February 24th, 2010 at 7:48 pm
We have three cafs trucks, two wild land and one class A pumper. I wouldn’t give up one of them, they save a lot of water usage and have a fast knock down. Preventative maintence will make your investment last for years. Our oldest unit was pruchased in 1999 and still going strong.
February 25th, 2010 at 12:41 pm
A few real world FAC’s concerning CAFS and water.
Fact #1 - CAFS is very expensive ($25 - 40 thousand per unit)
FAct #2 - Water is free.
Fact #3 - CAFS is 99.9% water
Fact #4 - Water is free. (same as fact #1)
Why are we spending thousands to save water?
Fact #6 - CAFS is very expensive and complicated to run and maintain and without proper maitainance it will not work.
Fact #7 - A typical water pump is relatively simple and inexpensive to maintain and can be run with very simple instruction.
Why are we making this whole process of fighting fire more difficult in this day and age in the quest to save water?
Fact # 8 - Water is free. ( same as Facts 2 & 4)
Fact #9 - Plain water when applied at the PROPER flow rates and GPM has the same effect as CAFS for knockdown.
Fact #10 - Flow rates and GPM are the SAME for CAFS as they are for PLAIN WATER. Hydraulics cannot be changed.
SOMEBODY please help me understand what is wrong with plain water??
February 25th, 2010 at 7:38 pm
Water is not free. CAFS increases the effectiveness of water and that IS important when water supplies are critical or non existant. In our District, rural water supplies do not include fire suppression and for the most part water districts run their supply through lines way to small to use. USE TENDERS!???! The most dangerous apparatus in the fire service. No thank you. Let me stay with our 100% CAFS fleet where we use less water, put the fire out faster, do less property damage, and have fewer hose handling mishaps and injuires. Thank You. Then again parts of Texas are classified as semi-arid.
February 26th, 2010 at 4:29 pm
Oh Henry…
FACT: Foam extinguishes in much less time than water
FACT: Foam is safer for firefighters–less exposure to fire and carbons, less stress as hoses are lighter and less rekindles
FACT: “Water is the new oil”…many U.S. cities are struggling with a lack of water!
FACT: Less than 1% of Class A foam is required and 1/8 the water when used together.
FACT: CAFS is not complicated if you are trained on the system.
FACT: Knockdown is significantly lower!
FACT: MUCH less water used and less rekindle.
Honestly!
February 26th, 2010 at 5:58 pm
There is nothing wrong with plain water, the addition of foam and air to the water allows it to do its job better.
Fact #1 As a fire chief I do not think 10% of the apparatus price is very expensive for what I get.
Fact #2,4,8 Although water is free, it is getting more scarce in certain areas of the US
Fact #3 It is actually about 80% water for structural firefighting.
Fact #6 and 7 They are not complicated to run today. They do require more maintenance.
Fact #9 CAFS is proven to be about 5 times more effective than plain water for extinquishment.
Fact #10 In a given hose there is less water flow to make up for the air in the hose.
February 26th, 2010 at 10:41 pm
Fact? #1 I would object to the adjective “very”. A 10% portion of an apparatus is a significant percentage but as a fire chief with three CAFS engines I think it is a tool that is worth the cost.
Fact? #2,4,8 Yes, water is cheap, not free. In the city I live in the wells and distribution system is not free. Water in some areas of the US can be scarce and restricted during some times. Because a natural resource is cheap should we waste it?
Fact? #3 Actually for structurally firefighting CAFS is about 80% water.
The investment in CAFS not only saves water but it also is safer for my firefighters because of the fact that we do exterior attacks first. The quicker knockdown also means that my firefighters are spending less time fighting fire.
Fact? #6 Yes there is an added expense to own for maintenance, but again I could not classify it as “very” expensive. It is no more difficult to operate than plain water engines, ask my engineers.
Fact? #7 See fact? 6.
Fact? #9 Comparing like flows CAFS has been proven to be about 5 times more effective than plain water.
Fact? #10 What is your point?
Again plain water works, I think that has been proven since fire was discovered. Horse travel also works but we advanced from that.
February 27th, 2010 at 4:47 pm
I am not going to get into a he said she said debate but will offer the following:
We have been using CAFS for 11 years with great success, and don’t plan on going back to water only. We are a Volunteer Department with limited staffing and manpower concerns. CAFS has helped greatly in that. For us we have access to tons of water, buts it’s not free – it takes time, men and equipment to move it, for us these are in limited supply. CAFS allows us to use the water we show up with (2000 Gallons) to be used more effectively, or maybe the word should be completely- as compared to water alone.
March 9th, 2010 at 2:52 pm
To all the CAFS Lovers. Please read the following article that appreared in Fire Chief Magazine. I believe Class A form will assist with extinguishment of Class A material in many cases. I am not convinced that it is necessary to use CAFS to apply it. CAFS has many dangerous aspects and should not be used during interior fire attack.
Heat Stress
Oct 1, 2007 12:00 PM
By Holger de Vries
The German city of Tübingen has a population of 84,000 and is situated 18.5 miles southwest of Stuttgart, in the state of Baden-Württemberg. In the early hours of a December morning, two firefighters died while attacking a structure fire with foam. It was the first such deaths for the nation.
The fire department operates 11 volunteer fire companies and including a central downtown station with a daytime crew of 12, of which seven work in the dispatch center and five are assigned to workshops on premises and respond to emergency calls citywide as first response and to support the local fire companies. There are about 600 volunteer personnel responding to 350 non-EMS calls annually.
On Dec. 17, 2005, the unit had two fatalies. Six months later, the state finished its investigation. Here’s what happened.
At 2:55 a.m. Tübingen’s Platoon 1 turned out to a reported working fire about 1.5 miles away from the downtown fire station. There were no paid crew available at night. The first crews arrived on scene at 3:01, and consisted of one senior officer, two pump companies, and one ladder company.
The crew found a 2H-story historical timber-frame construction with brick overlay, extensions and a peaked roof. It had wooden ceilings, mostly open wooden stairs, and wooden internal walls partly insulated with hard polystyrene insulation. The ground floor was used as bicycle workshops and upper floor as artists’ studios. Firewood was stored in many rooms around stoves. Investigators later determined that reckless handling of ashes from a wood stove started the fire on ground floor. It spread into first and second upper floor and attic.
Firefighters found flames showing from a ground-floor window at 3:06. Two-man Team A initiated suppression with a 2-inch line from the outside though the window. Then Team A entered the structure for interior attack, while two-man Team B prepared a second 2-inch line at the ladder basket to address the upper floors.
Between 3:15 and 3:25 the initial attack seems to be successful. The incident commander through the crew commanders instructs a third two-man Team C to enter the structure through a third door to investigate the stairs to the upper floors, progress to the upper floor, and take a 2-inch Compressed Air Foam System hand line.
In Germany, fire departments first deploy one or several lengths of 3-inch hose from the pump to the fire, and then use a distributing valve (called a water thief) with three valved outlets to connect to the 2-inch attack lines.
Team C belonged to pumper 2, but were briefed by the crew commander of pumper 1 that there might “still be people in the building”, although the likelihood of this was considered relatively small. Besides taking the CAFS hand line, the team wore complete turnout gear and full positive-pressure SCBAs, and carried a hand light, an ax, a radio and two escape filter hoods for possible casualties.
On their way into the building, Team C met Team A on the ground floor, temporarily supported their fire suppression, then told them that Team A would remain on the ground floor while Team C advanced upstairs into the first upper floor. At that time, the smoke conditions still were moderate, and no fire was showing up the stairs or on the upper floors.
After the incident, investigators asked why Team C left doors on the first upper floor leading to rooms untouched and advanced seemingly directly into the second upper floor attic. This might have been because those doors were rather flush with the wall and the team might not have recognized them. This might have led to Team C walking past presumably at least one burning room unnoticed. During their advance, Team C did not radio their progress to the crew or incident commander. The officers assumed Team C was on the first upper floor. More access into the building was made on the ground floor and suppression appeared to be successful.
At 3:27 another two-man team, which was not letter-coded in the investigation report, deployed a third CAFS line. That team set up for an outside attack against flames showing at the windows of the first upper floor. Between 3:28 and 3:41, smoke conditions on the ground floor were described as light and as moderate on the first upper floor. This was probably an assessment from the outside since Team C had not communicated with command.
At about 3:35, a two-man Team D was sent into the building to relieve Team C at their assumed first upper floor position, after Team C reported having two-thirds of the initial air remaining.
Investigators could not determine when Team C connected their regulators to their masks. They were seen leaving the staging area unconnected, so it was assumed that they connected and began using their air tanks upon entering the building. Investigators determined that laying the hose line along that staircase involved a high physical workload, thus requiring more air so that the time span of approximately 10 minutes until the two-thirds-full message appeared realistic.
Team C sent a one-third-full message between 3:35 and 3:38 and the relief Team D advanced. Before Team D met with Team C, Team C radioed for more hose. This was overheard by Team D who were just about to enter the building, advancing pressurized hose loops of Team C’s attack line on their way up to relieve Team C. There was still no visual or voice contact between Teams C and D. Team D later described the smoke conditions as light, getting a bit thicker towards the upper floors, with good visibility, and no flames showing.
However, at 3:41, flames were spotted at the rim of the roof and the fire behind the windows on the first upper floor re-ignited.
A member of Team D said that as they “went up the stairs from ground floor to first upper floor we realized a tremendous heat. On the first upper floor I encountered one door that had already burnt down halfway. I could see that the room behind that door was fully involved. My team leader told me that due to the heat we could not advance further. [One of the firefighters was wearing a leather coat instead of a standard turnout coat]. We were planning to retreat temporarily, and get another hose line for ourselves.”
This meant that the escape route for Team C was becoming blocked.
At 3:45 the roof showed no more flames. Photographs taken at the time show the color of the smoke changing from black to white, indicating that at that time Team C should still have been fighting the fire, since no other attacked had been directed at the roof.
Between 3:46 and 3:49, a couple of incidents occurred. Team D, still on the head of the stairs on the first upper floor, saw the hose line to Team C bursting “with a clear, significant sound, without anything (no glowing embers, etc.) touching the hose.” They tried to patch the hose line with their gloved hands but failed due to the pressure. They went for replacement line.
Team D returned to the ground floor and demanded a 2-inch line from the bystanding firefighters. Without waiting for that replacement attack line, Team D went back upstairs and directed the foam pouring out of the burst hose into the adjacent burning room. Eventually Team D had a replacement hose line and began spraying the burning room to follow the burst hose line deeper into the building to relieve Team C.
At about 3:49, Team C sent a mayday message over a portable radio saying, “hose is burst and way out is blocked.” A second, weaker mayday was received later, but Team C still did not reveal their position. Further calls to Team C remain unanswered.
Two more two-man teams were sent in and by 4:16 the first member of Team C was found next to his ax on the second upper floor. He was approximately six feet from the stairs with his SCBA mask removed but his escape mask donned. Another rescue team found the second team member 15 minutes later only six feet further away, with turnout gear and SCBA mask completely in place. Both firefighters died of carbon-monoxide intoxication.
These fatalities were caused partly by the historical wooden construction plus the newer modifications, which did not separate the staircase from other rooms like contemporarily required. Team C did not realize that they were running into a firetrap when they left the rooms on the first upper floor unattended. Investigators assumed that they returned into the second upstairs floor attic after realizing that they could not negotiate the way downstairs and looked for an alternative escape route.
Preliminary calculations and trials run after the incident reveal that hose lines filled with compressed-air foam are more prone to fail than those filled with water due to radiant heat. Double-jacketed hose is not used in Germany or likely any other European nation. The type of hose used by German fire departments can be compared to that of Niedner’s HDI-600 or Niedner’s Hotline.
The police crime lab found that the burst hose line could be connected with the hose’s high exposure to radiant heat on the first upper floor. It was found that at temperatures of around 394°F (200°C), hoses fail sooner when filled with compressed-air foam than when filled with water. The reason lies in the reduced water contents and thus in the reduced heat capacity of foam.
Based on these findings, the state chief fire officer of Baden-Württemberg issued a leaflet on using CAFS for structural firefighting, which was later adopted by other German states. This leaflet states the hoses used with compressed-air foam can fail sooner than hoses lines with water. This was observed under radiant exposure as well as when exposing the hose lines to glowing embers. The measured time differences are several minutes with water versus within a minute for CAFS. It gets more critical if the compressed-air foam does not flow because the nozzle is closed. Fire departments are advised not to use CAFS, if the hose lines may be exposed to heat or hot particles in due course of the operations.
During firefighting operations, the exposure of hose lines to heat or hot particles is a given. Compressed-air foam could however be used for single room-and-contents fire with a safe attack route in a brick-and-stone environment. Yet even in a brick-and-stone environment there usually will be combustible furniture, wall decorations, partitions or false walls, that expose hose lines to heat or hot particles. A safe attack route — as well as a safe escape route can only be attested in retrospect — when the fire is out, and the troops are all out again.
Holger de Vries joined the German fire service in 1981 and is now volunteer platoon commander with the Hamburg Fire & Rescue Service. He served in the German Navy and as a reserve officer is now one of the instructors at the German Navy Damage Control School. He earned a Ph.D. in safety engineering with a major in fire engineering in 1999; he has worked in Hamburg as a freelancing consulting engineer and as sworn-in expert witness in that field. In 2006 he began as a lecturer in the rescue-engineering program at the Hamburg University of Applied Sciences.
History in Foam
In hearsay and in some manufacturers’ literature it is claimed that compressed-air foam systems had been used successfully during World War II. As in many cases, a look into original sources produces some interesting details.
Since the 1930s, the British Royal Air Force has continuously developed airfield crash tenders in order to match the increasing military air traffic as well as the increasing size of the individual aircrafts. The tenders were built on various different chassis (mostly Crossley TPY 3-ton 6×4, Crossley FEI 6×4, Crossley Q30 4×4, and Fordson W.O.T.1 6×4). Yet they basically carried the same fixed firefighting system, which consisted of a water tank that held 900 liters, a Saponine foam agent tank that held 127 liters, and a PTO-driven water pump to which an emulsifying column and expansion chamber were flanged. The assembly of these three was referred to as the “foam pump.” Until the mid-1940s, the RAF tenders also carried four carbon dioxide extinguishing cylinders that discharged in pairs and were completely independent of that water-foam system.
A look at the RAF’s fire manual (Air Publication 957 Part 2) describing the foam pump’s operation shows that this isn’t a foam pump. Instead, it is an “air leaking displacement pump” with something similar in design to a classical expansion nozzle permanently fixed to it, then a CAFS into which air is induced forcefully.
Another myth that is often quoted says that the U.S. Navy had used CAFS in the 1940s and 1950s. It is correct that the U.S. Navy developed trailer-mounted triple-pump pressure from generators. However, these were not developed for manual or structural firefighting, but to use these trailers as one possible means to inject foam into oil tanks using subsurface injection during oil farm fires. So again, a look at the original sources draws a much clearer picture of the background, intended application, and limitations of compressed-air foam.
CAFS Fireground Performance
If a driver punches a car’s cruise control plus button to increase the speed from 60 mph to 65 mph, it takes a few seconds until the engine revs up to match the required 65 mph. Comparing this to a compressed-air foam system would mean that the “CAFS cruise control” in theory must be able to go from 0 mph to 100 mph and back within two seconds.
CAFS requires a rather complex and timely interaction of various sensors (for water, foam agent and air flow and/or pressure) and actuators (water pump, foam agent pump, air compressor or tank), which are interconnected by valves. The whole ensemble needs some kind of processor to compare readings and settings, and to trigger changes such as pump revolutions.
Consider the flows of 2- and 3-inch hoses at pressures around 70 to 100 psi. As an example, let’s choose a 2-inch line at 80 gpm. First, consider water only. The velocity of the water in that hose line is approximately 8 feet per second. That means that every bit of water travelling through the hose will need approximately six seconds of travel time. If the attack line is six lengths of hose long, the overall time from pump outlet to nozzle will amount to 36 seconds.
Since water can be considered incompressible, a water stop at the nozzle will immediately be transmitted back to the pump and can be seen on the pressure meter and felt by any pressure sensor near that pump. However, because CAFS is compressible, the signal of a water stop — which is travelling back through the hose line to the pump will — be delayed in time as well as in sharpness. Without a decent sensor signal there is no proper adjustment of the system.
On a real fireground, however, nozzles will not be opened and closed only once. Firefighting is a very dynamic process requiring hose operators to immediately respond to changes. This includes opening and closing the nozzle, and adjusting flow and, if possible, spray pattern to match the balance between efficient knockdown and avoiding excessive water damage. The flow of attack lines over time can be recorded.
If the numbers of the first example are applied again, then one bit of water will need approximately 36 seconds to travel from the pump outlet to the nozzle. Within these 36 seconds, the nozzle operator might have closed and opened the nozzle a few times (between minutes four and six). The CAFS control system is lost and will not be able to match the requirements, even if the dead time (time from when all necessary signals are there to when the output is adjusted) is zero.
Some kind of foam will exit the nozzle tip. However, it is doubtful which properties it has and whether this has anything to do with the control panel’s wet and dry settings. The promises that these settings make only can be fulfilled by the system if it is kept running under the same constraints, such as revolutions.
This mismatch also applies to noncompressed air foam systems, systems that only have a foam agent proportioner to which a line is connected that is dynamically opened and closed. So bits of water-foam solution will arrive at the nozzle that may have on an average 0.5% foam agent. That means that some bits will have 0% and some will have maybe 3% foam agent. With Class A foam that is in reality not a big deal, because there will basically always be enough foam agent inside the hose line to allow for improved wetting capabilities.
Hose Diameter Flow per Minute Velocity Travel time [sec] through 50 feet of hose
[liters] [gallons] [m/s] [ft/sec]
2 inches 100 26 1 3 19
2 inches 200 53 2 5 10
2 inches 300 79 2 8 6
2 inches 400 106 3 10 5
3 inches 100 26 0 1 40
3 inches 400 106 2 5 10
3 inches 600 159 2 7 7
3 inches 800 211 3 10 5
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