Post on 17-Dec-2015
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)
Design Methods for Subsurface Injection Foam Systems (cont.)
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)
Design Methods for Subsurface Injection Foam Systems (cont.)
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
(%)
Design Methods for Subsurface Injection Foam Systems (cont.)
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.
Surface Application Low Expansion Foam Systems (cont.)
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
Surface Application Low Expansion Foam Systems (cont.)
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
Dike Protection Low Expansion Foam Systems (cont.)
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
Dike Protection Low Expansion Foam Systems (cont.)
Design Methodology Step #1
Calculate dike area Step #2
Determine application rate(outlets & monitors) Determine discharge times(outlets &
monitors)
Dike Protection Low Expansion Foam Systems (cont.)
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???