Chapter 3 Low Expansion Foam Systems

Unit 4

Low-Expansion Foam System Design

NFPA 11

Standard for Low Expansion Foam

Which one is safer?

Flammable or Combustible???

Flammable Liquids

Flammable liquid is defined as a liquid that has a flash point below 100ºF and having a vapor pressure not exceeding 40 psi

What is flash point? Lower Flammable Limit

What is vapor pressure? Closed container, vapor-air mixture above the

liquid

Combustible Liquids

Combustible liquid is defined as a liquid that has a flash point at or above 100ºF

Low-Expansion Foam

“Low-expansion foam systems are used when a blanket of foam is needed to float on the horizontal surface of a flammable or combustible liquid.”

Limited vertical surface protection Use when Coating and O2 Displacement

are the preferred method of extinguishment

Low-Expansion Foam (cont.)

Coating Separates the fuel from the flame Blocks admission of air to the combustion

process (i.e. oxygen dilution/separation of the fire)

Cools the surface of the fuel

Low-Expansion Foam (cont.)

Low-Expansion foam is an appropriate substitute for water when water is heavier than the Flammable/Combustible liquid being protected.

Specific gravity

Expansion Ratio

Expansion Ratio

Low Expansion Foam Up to 20:1 Typically 8:1

Medium Expansion Foam 20:1 to 200:1 Typically 100:1

High Expansion Foam 200:1 to 1000:1 Typically 500:1

Expansion Ratio (cont.)

The expansion ratio of foam is computed by measuring the volume of the foam produced after water and air are added and comparing that volume to the original volume of foam concentrate used

Low-Expansion Foam = up to 20:1 of the hazard

The Components of Foam

Components of Foam

Air Contained within Foam bubbles

Water Delivered at a specified density in

GPM/SQ.FT Foam Concentrate

Injected into the water stream at a specific percentage

Components of Foam (cont.)

Foam concentrate is usually stored in drums or barrels 1st - the Foam Concentrate is mixed with water to

make a Foam Solution 2nd - the Foam Solution flows through the piping

system to the hazard location 3rd - the Foam Solution is mixed with air (disch.

devices) at the specified rate to make FOAM “It’s like blowing bubbles”

Types of Foam

Types of Foam

Protein Foam Fluoroprotein Foam (FFFP) Aqueous Film-Forming Foam (AFFF) Alcohol-resistant Foam Chemical Foam

Protein Foam

Expansion ratio between 8:1 and 10:1 Protein-based animal additives (hooves,

feathers) Hmm, Hmm, Good!… Can be effective on hydrocarbon fires, but

absorbs fuel and tends to fail, no film What does hydrocarbon mean?

Organic Compounds that contain only carbon and hydrogen (i.e. Natural Gas, Petroleum, Coal, etc)

Protein Foam (cont.)

Shorter shelf life More frequent replacement compared to

other types of Foam May not maintain “floating” above the fuel

Fluoroprotein Foam

Protein Foam Contains fluoroprotein additives

Less absorption of fuel Film-Forming fluoroprotein (FFFP)

More effective than regular Fluoroprotein Produces a film barrier between the foam and

the fuel

Protein-based Foams(Summary)

Ranked by Effectiveness Film-Forming Fluoroprotein Foam (FFFP) Fluoroprotein Foam Protein Foam

Aqueous Film-Forming Foam (AFFF)

Synthetic Foam Recommended for flammable liquids in

storage tanks Thin aqueous film that separates the foam

from the fuel Readily available Foam of choice for many applications

including Aircraft Hangars protection

Alcohol-resistant Foam

Used for the protection of alcohol-based flammable liquid fires

Effective because the alcohol in the flammable liquid does not collapse the foam bubbles (water absorption) like other foams

Forms a polymeric membrane between the foam and the fuel

Chemical Foams

Depends on chemical reaction within the Foam Solution to create air bubbles (Foam)

Obsolete due to AFFF and FFFP

Proportioning Methods

Proportioning Methods

Foam Concentrate must be mixed with water by a Foam Proportioner Ensures proper expansion Ratio and proper

proportions Example 6% Foam Concentrate

6% Foam Concentrate, 94% Water

Types of Proportioners

Venturi /In-Line Proportioner Pressure Proportioner Balanced Pressure Proportioner

Venturi /In-Line Proportioner

Water moves past the metering orifice, thus creating negative pressure at the orifice that forces (pulls) Foam Concentrate into the water stream of the Venturi

Foam is dependent on metering orifice size, but is typically 1%, 3%, or 6% mix

Pressure Proportioner

Draws a portion of incoming water stream into the tank holding the Foam Concentrate This is done in an effort to pressurize the tank where

the foam concentrate is stored Collapsible bladder holds the Foam Concentrate Water increases the amount of pressure on the

bladder tank, thus forcing foam concentrate out of the bladder and towards the proportioner

Balanced Pressure Proportioner

Uses an atmospheric foam concentrate tank Uses a pump to pressurize the concentrate and

force it toward the proportioner A proportioner that balances the pumped

concentrate pressure to the water supply pressure, mixing the two at the correct ratio

Types of Foam Systems

Types of Foam Systems

Mobile and Portable Apparatus Semi Fixed Systems Fixed Foam Systems

Mobile and Portable Apparatus

Fire Departments Hand (portable) F.D. Truck Wheeled Platform (Mobile)

Selection of Foam or Foam Equipment should match the expected flammable or combustible liquid

Semi Fixed Systems

Permanent Foam makers and outlets Spaced as needed or required Piped to a connection

Located a safe distance from hazard

Semi Fixed Piping used in conjunction with mobile or portable foam equipment Mobile or portable foam equipment should be able to

serve multiple semi fixed piping installations Detection system, continuously attended central

station, on-site fire brigade is recommended

Fixed Foam Systems

This course is focused on Fixed Foam Systems Automatic Self-contained No manual intervention

Specifically fixed storage tank foam F.P. and fixed aircraft hangar F.P.

Storage Tank foam fire protection

Four types of protection systems we will discuss in FET-222 Subsurface injection Surface application Seal protection for floating roof tanks Dike protection

Subsurface Injection – Low Expansion Foam Systems

Subsurface Injection Foam Systems

Storage tank w/fixed permanent roof Prevents the collection of rainwater above or

below flammable/combustible liquid Foam is applied below the surface of the

liquid, and floats to the top of the fuel surface

Subsurface Injection Foam Systems

#1 Dedicated foam line Piping and nozzles at bottom of tank with nozzles in the

liquid, dedicated solely to foam injection Nozzle spacing provides uniform disbursement of foam

to surface of the liquid (more gentle and uniform than surface application of foam)

Not practical for existing tanks

#2 Injection into product (liquid) line Tapped directly into the tank product line Practical for existing tanks

Subsurface Injection Foam Systems (cont.)

High back-pressure foam makers required on both types of subsurface injection types

Design Methods for Subsurface Injection Foam Systems

Step #1-Calculate fuel surface area The circular area of the exposed fuel at the

upper level of the tank Area=(pi)(r)^2

Step #2-Determine application rate (R) and discharge time (T) See Figure 3-8

Design Methods for Subsurface Injection Foam Systems (cont.)

Step #3-Calculate minimum foam discharge rate Foam Discharge rate Dgpm=(Area) (Rate)

D=foam discharge rate (gpm) A=tank surface area (Step #1) R=application rate (See Figure 3-8)


Step #4-Calculate foam concentrate quantity Foam Concentrate Quantity Q=(A)(R)(T)(%)

Q=primary foam concentrate quantity (gal) A=tank surface area (Step #1) R=application rate (See Figure 3-8) %=concentrate percentage for foam selected

1%(0.01), 3%(0.03), (6%(0.06)


Step #5-Determine the number of subsurface foam application outlets See Figure 3-9

Step #6-Determine supplementary protection requirements See Figure 3-10

# of addl. hose streams x 50gpm

See Figure 3-11 (# of addl. hose streams) x (50gpm) x (Operating Time) x

(%)


Step #7-Determine total discharge rate Dt=D+Ds

Step #8-Determine total foam concentrate quantity Qt=Q+Qs

Step #9-Hydraulically calculate the system

Break

Surface Application - Low Expansion Foam Systems

Surface Application Low Expansion Foam Systems

Surface application discharge devices are designed to roll a thin blanket of foam over the surface area of the fuel with fixed discharge outlets permanently located above the fuel surface See Figures 3-12, 13A, 13B in textbook

There are two types of discharge devices

Surface Application Low Expansion Foam Systems (cont.)

Discharge devices Type I Outlet Discharge Devices

Designed to deliver foam onto the liquid surface in a very gentle fashion

Two types Porous Tubes – tube overcomes diaphragm pressure and

drops into tank from the Foam Chamber Foam Trough – Chute securely attached to the inside of

the tank, “like pouring concrete”

These outlets are designed to extinguish fire with a minimum of Foam-producing materials.


Discharge devices (cont.) Type I Outlet Discharge Devices

Considered obsolete because nearly all currently manufactured foams are suitable for use with Type II discharge outlets


Discharge devices (cont.) Type II Outlet Discharge device

Designed to deliver foam (less gently than Type I Outlets) onto the liquid surface, but to lessen submergence of the foam and agitation of the surface

Commonly called Foam Chambers Most Foam Chambers are of a Type II discharge outlet

design, since they are normally suitable for use with modern foams

Seal Protection forFloating Roof Tanks

Seal Protection forFloating Roof Tanks

What is a floating roof? A floating roof floats on the surface of the flammable

liquid, rising and falling as the liquid is added to or removed from the tank

The floating roof allows no space between the bottom of the roof and the surface of the liquid, no vapor buildup

What is seal protection? A system that involves building a dam around the

perimeter of a floating roof and filling the seal area with low expansion foam

Seal Protection forFloating Roof Tanks (cont.)

What part of the floating tank gets Foam protection? The space between the edge of the floating roof and

the perimeter of the tank The (weather) seal that covers this area requires Foam

Protection This involves building a “Dam” of Foam around the perimeter

of the floating roof and the tank

Some cases require Foam Distribution Piping to penetrate the (weather) seal Seal must be able to hold the Foam

Seal Protection forFloating Roof Tanks (cont.)

Spacing of Discharge devices Top of Seal protection (foam dam)

Foam dam height 12 inches, Outlets-40ft max Foam dam height 24 inches, Outlets-80ft max

Protection below Seal (pipe penetration of seal) Mechanical Shoe seal, Outlets-130ft max Tube seal, Outlets-60ft max typically Foam dam required when 6 in or less between top of roof

and tube

Dike Protection Low Expansion Foam Systems

Dike Protection Low Expansion Foam Systems

Containment dike for tank farms will often have a supplemental Low Expansion Foam System

The dike area is flooded with Foam that will float on top of any flammable liquid that may have been spilled within the containment area

See Figure 3-19, Plan view

Dike Protection Low Expansion Foam Systems (cont.)

A dike protection system may also be recommended as supplemental protection fixed cone roof (FCR) floating roof tank (FRT) dike area

Systems can be portable or mobile under certain guidelines


Design Procedure Calculate dike area

Note: If a tank is installed with its bottom mounted to the floor of the dike, then the surface area of the tank may be deducted from the total dike area

Determine application rate and discharge times per NFPA 11

Calculate foam discharge rate and concentrate quantity

Determine the number of foam discharge devices required


Design Methodology Step #1

Calculate dike area Step #2

Determine application rate(outlets & monitors) Determine discharge times(outlets &

monitors)


Step #3 Calculate foam discharge rate Calculate concentrate quantity

Step #4 Determine # of foam discharge devices

required N=(2L+2W)/30

See page 11-19, NFPA 11

Low Expansion Foam Systems for Aircraft Hangars

Low Expansion Foam Systems for Aircraft Hangars

Aircraft that are stored or serviced in an aircraft hangar contain large amounts of flammable fuel

Servicing the aircraft offers numerous opportunities for the spilled fuel to ignite

Low Expansion Foam Systems for Aircraft Hangars (cont.)

NFPA 409 Standard on Aircraft Hangars

Low expansion foam systems not only smother flammable liquid pool fires on the floor, but effectively coat the aircraft skin with an effective exposure protection barrier.

Low Expansion Foam Systems for Aircraft Hangars (cont.)

Hangars are classified by three groups Group I, Group II and Group III

Aircraft hangar fire protection design can consist of low expansion foam systems Ceiling protection (coats skin)

Aspirated foam water nozzles (Air) vs. Non-aspirated sprinklers

Underwing protection (WOM) Water Oscillating monitors

Supplementary Hose protection

Truck Loading Rack Protection

Truck Loading Rack Protection

NFPA 11- Standard for Low Expansion Foam NFPA 16- Standard for the Installation of Deluge

Foam-Water Sprinkler and Foam-Water Spray Systems

NFPA 16A- Standard for the Installation of Closed-Head Foam-Water Sprinkler Systems

The point where flammable and combustible liquids are pumped from storage tanks to a truck

See Figure 3-25, Page 69

Hazards Associated with Truck Loading Racks

Most dangerous portion of the manufacture of a flammable or combustible liquid

Pumping the liquid involves Pressurization of the hose line that transmits the liquid

Pump could fail Hose could burst or become dislodged

from the connection to the truck

Hazards Associated with Truck Loading Racks (cont.)

Numerous other ignition sources: Smoking Electrostatic charges Truck Battery

Fire Protection Strategy for Truck Loading Racks

Roof protection Foam-water sprinklers or Foam-water spray nozzles

at the roof of the truck loading rack. Typically, at a maximum of 100 sq.ft.(10’ x 10’) i.e. Extra Hazard

Goal of Roof Protection To provide complete protection of the drainage area

The drainage area is the curbed area designed contain spilled flammable or combustible liquids as it flows towards floor drains. Note: Drainage area may not always coincide with the Roof area. The hazard area is always the drainage area, not the roof area.

Fire Protection Strategy for Truck Loading Racks

See Figure 3-28 Additional nozzles are aimed directly at

the point of connection of the hose to the truck

Additional nozzles are aimed beneath the truck to enable the sweeping of liquid from beneath the truck

See Figure 3-29

Summary

Use Protection of Flammable or Combustible liquids (Two-

dimensional) Expansion ratio – Low Expansion

Up to 20:1 Components of Foam

Foam concentrate, Water, Air Types of Foam

Protein, Fluoroprotein, AFFF, Alcohol-resistant, and Chemical

Summary (cont.)

Applications Subsurface injection Surface injection Seal protection Dike protection Aircraft Hangars Truck loading racks

Questions???

Chapter 3 Low Expansion Foam Systems

Documents

truck loading racks

outlet discharge devices

fire protection strategy

fixed foam systems

floating roof tanks

determine application rate

portable foam equipment

low expansion foam