hazardous materials awareness during fire incident...

Foam Systems

WILLIAM HICKS

MSc, CFEI, CFPS, IAAI-CFI, MIFireE, EFO, CFOD, F-IAFI Associate Professor

Eastern Kentucky University

William.Hicks@eku.edu

Objectives

Classify high, medium, and low-

expansion foams, given their respective

expansion ratios

Determine whether a liquid is flammable

or combustible

Know the advantages and

disadvantages of the currently available

varieties of low-expansion foams

Objectives (con’t.)

Design and calculate a surface or

subsurface low-expansion foam system

for the exposed fuel surface within a

flammable or combustible liquid storage

tank

Design and calculate a low-expansion

foam seal protection system for a

floating roof tank

Objectives (con’t.)

Design and calculate a low-expansion

foam dike protection system for a tank

farm

Design and calculate a low-expansion

foam system for an aircraft hangar

Perform a detailed layout of a low-

expansion foam system, designed in

accordance with NFPA 11

Objectives

Determine appropriate situations for the

use of low-expansion, medium-

expansion, and high-expansion foam

Discuss the differences in the

application and the methods of

extinguishment for low-expansion,

medium-expansion, and high-expansion

foam

Objectives (con’t.)

Perform a calculation of a high-

expansion foam system to determine

the rate of discharge and number of

high-expansion foam generators

required

Lay out a high-expansion foam system,

showing foam fences, generator

locations, and piping locations

Components of Foam

All foams contain three components

– Air, contained within foam bubbles

– Water, delivered at a specified density in

gallons per minute per square foot of applied

area

– Foam concentrate, injected into the water

stream at a specific predetermined

percentage

Fire-fighting foam: mixture of the foam

solution with air

Expansion Ratio

Expansion ratio: measure volume of the foam produced after air is added to the foam solution and compare that volume to the original volume prior to air addition

Expansion Ratio

Classifies Foam based on Expansion

Ratio

– Low Expansion = up to 20:1

typical - 8 : 1

– Medium Expansion = 20:1 – 200:1

typical -100 : 1

– High Expansion = 200:1 – 1000:1

typical -500 : 1

Types of Foam

Protein foam: contains protein-based animal additives

Fluoroprotein foam: contains fluorochemical additives to improve flow

Film-forming fluoroprotein foam: uses fluorinated surfactants to produce a fluid aqueous film for suppressing hydrocarbon fuel vapors

Types of Foam (con’t.)

Aqueous film-forming foam (AFFF): a

synthetic foam that forms a thin aqueous

film that separates the foam from the fuel

Alcohol-resistant foam: for the protection

of alcohol-based fires

Chemical foams: depends on the

initiation of a chemical reaction within

the foam solution to create air bubbles in

the foam

Proportioning Methods

Foam proportioner: ensures delivery of

the precise ratio of foam concentrate to a

foam solution

Venturi proportioner: uses the negative

pressure created by water flowing past

an open orifice to draw foam concentrate

into the water stream

Proportioning Methods

Aspirating Foam Maker

Proportioning Methods (con’t.)

Pressure proportioner: draws a portion

of the incoming water stream to

pressurize the tank holding the foam

concentrate

Balanced pressure proportioner: uses an

atmospheric foam concentrate tank, a

pump to pressurize the concentrate and

force it toward the proportioner

Types of Foam Systems

Mobile and Portable Apparatus

Semi-fixed Systems

Automatic Fixed Foam Systems

– Subsurface injection

– Surface application

– Seal protection for floating roof tanks

– Dike protection

Applications for Low-, Medium-, and High-

Expansion Foams

Subsurface Injection

Low-Expansion Foam Systems

Subsurface injection: foam is discharged below the surface of a flammable or combustible liquid

A low-expansion foam is used for this application

Design Method for Subsurface Injection

Subsurface Injection

Low-Expansion Foam Systems

Ex. 4-1: Subsurface Injection

Ex. 4-1: Subsurface Injection

Table 4-1

28

Table 4.2

29

Table 4.3

30

Table 4.4

31

Surface Application

Low-Expansion Foam Systems

Surface application: rolls a thin blanket of foam over the surface area of the fuel

Design Method for Surface Application

– Type I discharge outlet: delivers foam onto the liquid surface in a gentle fashion

– Type II discharge outlet: applies foam less gently than a Type I outlet, but submergence and agitation are kept to a minimum

Surface Application Low-Expansion Foam

Systems (con’t.)

Surface Application Low-Expansion Foam

Systems (con’t.)

Ex. 4-2: Surface Application

Ex. 4-2: Surface Injection

Table 4.3

37

Table 4.4

38

Table 4.5

39

Table 4-6

40

Table 4-7

41

End Part 1

42

Seal Protection for Floating Roof Tanks

Floating roof: tank roof that floats on

the surface of a flammable or

combustible liquid

Seal protection: filling or covering the

seal area with low-expansion foam

Seal Protection for Floating

Roof Tanks (con’t.)

Sectional view of a floating roof tank with above-seal low-

expansion foam protection using a foam dam

External Floating Roof Tank

http://www.hghouston.com/images/rooftank.jpg

Types of Seals for Floating Roof Tanks

Source: Figure 5.3.5.4.5 – NFPA 11

Source: Figure 5.3 C & D – NFPA 11

Design Procedure for Floating Roof

Tank Seal Protection

Low-expansion foam protection of floating roof tank seals uses following methodology

– Calculate foam distribution area

– Determine application rate and discharge time

– Calculate foam discharge rate and concentrate quantity

– Determine spacing of discharge outlets

– Determine number of discharge devices

Design Procedure for Floating Roof Tank

Seal Protection (con’t.)

Methodology (con’t.)

– Determine supplementary hose demand

and concentrate quantity

– Calculate supplementary hose demand

foam quantity

– Hydraulically calculate the system

Dike Protection

Low-Expansion Foam Systems

Tank farm: an enclosure containing tanks that store flammable or combustible liquids, surrounded by a containment dike

Dike protection systems: dike area is flooded with foam that floats on top of a flammable liquid that spills within the containment dike

Plan and sectional view of a dike protection system with

low-expansion foam protection (part 1)

Dike Protection Low-Expansion Foam

Systems (con’t.)

Dike Protection Low-Expansion Foam

Systems (con’t.)

Figure 4-18. Plan and sectional view of a dike protection

system with low-expansion foam protection (part 2)

Formula to Calculate Dyke protection

A dike measuring 300 feet by 300 feet surrounds a

tank farm. Assume a fuel with a flash point less than

100 F and assume the use of’ fixed discharge

devices. Draw a 6% AFFF low expansion foam

system, and calculate the minimum amount of low

expansion foam concentrate that would be required

for the protection of the dike area. Also determine the

minimum amount of foam solution required, and the

minimum amount of water that must be available for

this design.

56

1. Calculate dike area.

A = (L) ´ (W) = (300) ´ (300)

A = 90,000 square feet

2. Application rate = 0.10 gpm/square

foot for fixed discharge on outlets

Discharge time = 30 minutes (assume

flash point less than 100 F)

57

3. Calculate foam discharge rate and

concentrate quantity, using 6% AFFF

foam concentrate.

D = (A) ´ (R) = (90,000) ´ (0.10)

D = 9000 gpm

Q = (A) ´ (R) ´ (T) ´ (%)

Q = (90,000) ´ (0.10) ´ (30) ´ (0.06)

Q = 16,200 gallons 6% AFFF

concentrate

58

4. Determine number of foam discharge

devices required.

𝑵 =𝟐𝑳+𝑾

𝟑𝟎

N= 𝟔𝟎𝟎 + 𝟔𝟎𝟎 / 30=40 Devices

59

Low-Expansion Foam Systems for Aircraft

Hangars

Low-expansion foam systems smother

flammable liquid pool fires on the floor

and also effectively coats the aircraft

skin

Group I Aircraft Hangars

Group II Aircraft Hangars

Group III Aircraft Hangars

Aircraft Hangar Foam System Design

Ex. 4-5: Aircraft Hangar Low-Expansion Foam

System Application

Ex. 4-5: Aircraft Hangar Low-Expansion Foam

System Application (con’t.)

Ex. 4-5: Aircraft Hangar Low-Expansion Foam

System Application (con’t.)

Loading Rack Protection

A loading rack is the critical point where

flammable or combustible liquids are

pumped from or to storage tanks to or

from a truck or rail car

Hazards Associated with Loading Racks

Fire Protection Strategy for Loading

Racks

Loading Rack System Design Procedure

Loading Rack Protection (con’t.)

Figure 4-29. Truck loading rack-ground sweep nozzles

Hydraulic Calculation of Foam Systems

After foam quantity estimates are made

– Designer draws CAD layout of the system

– Performs a comprehensive computerized hydraulic calculation of the low-expansion foam system

When hydraulically calculating a foam system, perform the calculation both to the supply and to the demand

Local Application Medium- And High-Expansion

Foam Systems

The majority of medium- and high-

expansion foam systems are total

flooding systems

Foam fills a volume to a specified height

For local application systems, NFPA 11

specifies minimum design criteria

Electrical Clearances For Medium- And

High-Expansion Foam Systems

Because foam contains water, application of foam could transmit electricity

– Designer must prevent this

The proximity of foam components to live electrical components must be coordinated

Electrical Clearances For Medium- And High-

Expansion Foam Systems (con’t.)

For altitudes greater than 3300 feet

(1000 m), the clearance is required to be

increased at the rate of 1% for each 330

feet (100 m) of altitude above 3300 feet

(1000 m)

See Table 5-1, Page 168 for electrical

clearances

Medium-Expansion Foam

The required depth of medium-expansion

foam over a protected hazard shall vary

as a function of expansion ratio

The depth of medium-expansion foam

shall be determined by tests

The rate of discharge of medium-

expansion foam shall be determined by

tests

The quantity of medium-expansion foam

shall be determined by tests

Applications For High-Expansion

Foam Systems

For hazards in which smothering of a

three-dimensional fire or oxygen

deprivation of a three-dimensional fire is

primary objective

A three-dimensional object requiring

high-expansion foam is one that requires

foam to be totally flooded and completely

covered to an elevation above the

highest level of the object requiring

protection

Applications For High-Expansion Foam

Systems (con’t.)

Figure 5-2. Sectional view of a flammable liquid pump

protected by a high-expansion foam system

Medium- and High-Expansion Ratio

Foams

Other Applications For High-Expansion Foam

Suppression Systems

High-expansion foam systems

– Primarily for extinguishment of flammable

liquid fires

– Should be specified with some degree of

caution with respect to personnel safety

High-Expansion Foam Systems For Robotic

Flammable Liquid Rack Storage

First consideration: personnel

Second consideration: fire protection

engineer must determine and solve the

performance objectives of the system

High-Expansion Foam Systems

For Aircraft Hangars

NFPA 409 permits high-expansion foam systems to be specified in lieu of the low-expansion foam systems

Overhead AFFF low-expansion foam systems protect flammable liquid spill fire hazards in aircraft hangars

High-expansion foam may be an answer to EPA concerns about low-expansion foam

High-Expansion Foam Systems As Dike

Protection

Successful use of high-expansion foam

has been employed

High-Expansion System

Extinguishment Mechanisms

High-expansion foam systems are suitable for the protection of

– Class A ordinary combustibles

– Class B combustible liquids

Extinguishment is accomplished by

– Smothering

– Cooling

– Insulating

– Penetrating

Design Of Total Flooding High-Expansion

Foam Systems

Total flooding method: completely filling a room or enclosure volume with a fire protection agent

Personnel Considerations for High-Expansion Foam

High-Expansion Foam Components

Determination of High-Expansion Foam Quantity

Design Of Total Flooding High-Expansion

Foam Systems (con’t.)

Duration of High-Expansion Foam Application (see Table 5-2, Page 181)

Discharge Rate

Number of Generators Required

Ex. 5-1: High-Expansion Foam

Ex. 5-1: High-Expansion Foam

Summary

High-expansion foam systems – Primarily for volumetric total flooding of

three dimensional objects

– Use a foam with an expansion ratio of

between 200 to 1 and 1000 to 1

Foam is expanded by a high-expansion

foam generator that resembles a large

fan

Summary (con’t.)

High-expansion foam extinguishes fire by smothering, cooling, insulating, and penetrating

NFPA 11 requires that high-expansion foam be flooded to an elevation exceeding 10% above the highest combustible, or 2 ft. above the hazard, whichever is higher

The rate of high-expansion foam discharge must consider foam breakdown that might occur if a sprinkler system is activated above the area protected by high-expansion foam

References

Design of Special Hazards and Fire Alarm

Systems - 2nd Edition-Gagnon

Fire Protection Systems-2nd Edition-Jones

Fire Protection Handbook-20th Edition-

NFPA

NFPA Standard

85

Questions?