Manchaca Fire Rescue

CAFS OPERATIONS CAFS Basics CAFS for the Firefighter CAFS for the Driver / Operator

It’s just foam… CAFS stands for: Compressed Air Foam System Terminology Review: Foam Concentrate: The raw foam liquid as it rests in its storage container prior to the introduction of water and air. Foam Solution: Mixture of foam concentrate and water after it leaves the proportioner but before air is added to it. Finished Foam: Extinguishing agent formed by mixing a foam concentrate with water and aerating the solution for expansion

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CAFS or NAFS NAFS = Nozzle Aspirated Foam System – The liquid in the hose is foam solution (concentrate + water) and the air is introduced at the nozzle. Typically a fog nozzle breaks up the stream into droplets and mixes the solution with air

CAFS or NAFS CAFS = Compressed Air Foam System – The product in the hoseline is finished foam. Solution, water and air are mixed at the apparatus before the stream is discharged into the hoseline. Typically this stream is discharged by a smooth bore tip since the fog nozzle is not needed to create finished foam. In fact, moving CAFS through a fog nozzle will degrade the quality of the finished foam.

Why CAFS? The process of injecting the foam concentrate and air at the apparatus and allowing it to mix as it travels down the hoseline results in a high quality foam with a small, uniform bubble structure. This process of mixing the finished foam in the hoseline is also called “scrubbing”. In order for the CAFS foam to discharge properly mixed, there are minimum hose lengths for lines so proper scrubbing can occur. 1 ¾” hose = 100 feet 2 ½” hose = 150 feet 3 “ hose = 200 feet

Why CAFS? The foam resulting form CAFS gives water a vastly increased surface area, allowing it to more efficiently absorb heat over the same quantity of straight water.

The foam will also adhere to vertical and overhead surfaces and remain in place longer, absorbing more heat in the higher portions of the room. The majority of straight water applications will run off and fall from these surfaces, exposing little of the water to the superheated areas of the fire.

Why CAFS? The energy of the compressed air in the hoseline provides extra propulsion to the stream. This gives a CAFS stream excellent reach and reduced friction loss characteristics.

The Flow Question With the increased efficiency provided by CAFS foam, it would logically follow that fires can be extinguished with decreased flow (gpm) compared to a straight water fire stream. It is IMPORTANT to remember that air bubbles do not extinguish fire – WATER EXTINGUISHES FIRE. There is still a critical application rate that must be applied in order for enough water to be present in the CAFS stream. This application rate insures that the fire is extinguished and firefighters are protected by the stream.

The Flow Question While it is not our goal to use less water with CAFS (with respect to the rate of application). We do have the potential to put the fire out faster due to the heat absorbing efficiency of the CAFS application (thus using less water due to less application time). The flow of a CAFS stream is a product of the gpm pumped into the line plus the cfm of air injected into the line. The quality of the foam will depend on the water-air ratio plus the percentage of foam concentrate injected into the stream.

CAFS Application Class A Foam: .1% to 1% .3% for interior fire attack .5% for overhaul and protective streams Interior Attack: Flow: .3% @ 100 psi (water) and ~35 cfm air (15/16” tip)

Class B Foam: 3% or 6% 3% for Hydrocarbon Fuels 6% for Polar Fuels and Ethanol Fuels

CAFS Application CAFS foam quality can be made to be “wet”, “fluid”, or “dry” This is determined by the ratio of water to air in the stream Water-to-Air Ratio

Application

Wet: 3:1

Interior Fire Attack

Fluid: 2:1

Overhaul Operations

Dry: 1:1

Wet

Blanketing and Structural Protection

Fluid

Dry

CAFS Application Foam quality can be controlled at the pump by the adjustments of the DO or at the nozzle by changes made by the nozzle operator. The DO controls the proportioner percentage, the gpm and the cfm. The nozzle operator controls the orifice size and gating of the nozzle shut off. – The smaller the nozzle orifice, the more the nozzle compresses the bubbles, making the foam wetter. Larger openings will “dry out” the foam.

CAFS Application Controlling CAFS quality via pump & nozzle 1 ¾” Hoseline

.3% with 15/16” tip .3% ~ .5% with 1 3/8” waterway .5% with 1 3/8” waterway 2 ½” Hoseline .3% with 1” tip .3% ~ .5% with 2” waterway

.5% with 2” waterway

“wet” foam “fluid” or “medium” foam “dry” foam with a 1:1 ratio from the pump “wet” foam “fluid” or “medium” foam

“dry” foam with a 1:1 ratio from the pump

Gating the nozzle will also affect foam quality

Hose Handling Nozzle Reaction – When operating with CAFS, air pressure will build in the hoseline when the line is shut down. This will cause a short surge and sharp nozzle reaction when the line is opened.

Water Hammer – While not eliminated, water hammer is less of a concern due to the compressible nature of the air mixed into the stream.

Hose Handling Application in interior fire attack: – In a pre-flashover state, apply to upper portions of walls and ceiling for maximum heat absorption. Foam will stick to the surfaces in the superheated atmosphere and continue to absorb heat. – In a post flashover state, “paint” the room in a box pattern (walls, ceiling, lower areas – seat of the fire – Foam is applied by “painting the surfaces” with foam

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Tank to pump Ensure correct foam tank is selected Activate foam system (defaults to .3% Class A) Activate Air compressor Set system to AUTO

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Establishing CAFS



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Establish correct discharge psi for water Activate air switch as hoseline is charged with solution

Water PSI 100 psi to any interior attack line 140 psi to any master stream

Establishing CAFS

SLUG FLOW • Water and Air will not mix without foam concentrate in the mix. • If air is injected into the hoseline with no foam in the system, slug flow is the result. • The nozzle operator will experience alternating pulses of water and air – This will produce an ineffective stream and is a hazard to interior fire crews.

• If you run out of foam or turn off the foam and TURN OFF THE AIR TO THE DISCHARGE LINE

Capacity – ENG503 The foam injection system on ENG501 is a 6 gpm Advantus foam proportioner. With a maximum output of 6 gpm of foam concentrate into the manifold, the system can support these foam solution flows: Class A Tank: 20 Gallons Class B Tank: 30 Gallons Air Compressor Maximum 200 cfm

Foam %

Max Flow of Water/Solution

.3%

2000 gpm

.5%

1200 gpm

1%

600 gpm

3%

200 gpm

6%

100 gpm

Minimum Flows These minimum flows allow for appropriate application rate (flow) for firefighting operations AND it provides enough flow in the line to minimize effects of hoseline kinking. 1 ¾” Line

90-100 gpm (minimum 100 psi)

2” Line

110-120 gpm (minimum 100 psi)

2 ½” Line

130+ gpm (minimum 100 psi)

Master Streams

Minimum 140 psi

Operation and Troubleshooting • Slug Flow: system is injecting air into straight water • Foam Strainer Plugged: system shows foam flowing but there is no foam being produced

• Switching Foam Tanks: (system normally left on “A” tank) select “flush” for 20 seconds and then select other tank • Ensure water is circulating at all times (the air compressor is water cooled from the fire pump) • ENG501 can supply straight water, class A or B (NAFS) foam, full CAFS, or air only depending on settings at the pump panel

Operation and Troubleshooting • The Water psi needle (black) and the Air psi needle (red) in the master discharge gauge should be within 20 psi of each other • Compressor should be ran for a minimum of 15 minutes at the weekly equipment check (remember to circulate water through the fire pump) • Normal temperature range for the compressor oil is 150-180°F (Alarms at 260°F)

• Foam system will read LOCON when concentration tank is low • Foam system will read NOCON when tank is empty. Shut down CAFS operation to prevent slug flow

LOCON

System Shut Down





1. Shut down air to discharge line 2. Switch compressor to “unload” to bleed pressure off the compressor system 3. Shut down compressor



4. Shut down foam system 5. Flush clean water through the line until clear (20-30 seconds typically)



The DO can leave the compressor on so the hoseline can be purged of water with the compressor air once the line is flushed