hazardous materials awareness during fire incident...
TRANSCRIPT
Foam Systems
WILLIAM HICKS
MSc, CFEI, CFPS, IAAI-CFI, MIFireE, EFO, CFOD, F-IAFI Associate Professor
Eastern Kentucky University
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
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
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
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
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
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
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
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
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?