Transcript Dry and Wet Chem Systems

Low Expansion Foam
• NFPA 11
• class B
– flammable liquids, FP < 1000F
– combustible liquids FP > 1000F
• forms blanket
• 2-D horizontal surface
• tank farms, airports etc.
Expansion Ratio
Classification
Range
Low expansion
Medium
High
up to 20:1
20:1 to 100:1
200:1 to 1000:1
Components of Foam
Air
– within bubbles
– most of volume
Concentrate
– to be mixed with water
– final concentration 3% or 6%
Water
– water + concentrate = solution
Types of Foam
Protein
–
–
–
–
older type
no film
from animal protein
little in use now
Types of Foam
Fluoroprotein
– better than protein
– forms film
Types of Foam
Aqueous Film Forming Foam
–
–
–
–
AFFF
most common for fuels
thin film
not for alcohols
Types of Foam
Alcohol Resistant
–
–
–
–
also “Alcohol type”
for small alcohols
methanol, ethanol etc
from membrane bewteen water and foam
Types of Foam
Chemical
– chemically generated foam
– obsolete
Proportioning Methods
• To mix concentrate with water
• either 3% or 6% concentrate in water
• 3 mechanisms
–
–
–
–
Venturi proportioner
Pressure proportioner
Balanced pressure proportioner
skip details
Types of Systems
Mobile
– fire dept. trucks
Semi-Fixed
– permanent piping, foam makers
– mobile concentrate and pump
Types of Systems
Fixed
–
–
–
–
Subsurface injection
Surface application
seal protection for floating roofs
dike protection
Sub-Surface Injection
•
•
•
•
•
•
Fixed roof storage tank
foam applied below surface
floats to surface
gentle, uniform application
fluoroprotein foam
has good fuel-shedding properties
Sub-Surface Injection-design
1. Calculate fuel surface area
A =( )( r)2
2. Determine application rate (R) and
discharge time (T)
• see 3.8
Sub-Surface Injection-design
3. Calculate discharge rate (D) and foam
concentrate quantity (Q)
D = (A) x (R)
Q = (A) x (R) x (T) x (%)
4. Determine the number of subsurface
application outlets
• see 3.9
Sub-Surface Injection-design
5. Determine supplementary requirements
– number of hoses (see 3-10)
– discharge time (see 3-11)
6. Calculate supplementary discharge rate
(Ds) and foam quantity (Qs)
Ds = (N) x (50 gpm)
Qs = (N) x (50 gpm) x (Ts) x (%)
Sub-Surface Injection-design
Total requirement for concentrate
Qtotal = Q + Qs
see example 3.1
Surface Application
• Fixed discharge units
• on rim of tank
Surface Injection-design
1. Calculate fuel surface area
A =( )( r)2
2. Determine application rate (R) and
discharge time (T)
• see 3.14
• note difference between types I and II
Surface Injection-design
3. Calculate discharge rate (D) and foam
concentrate quantity (Q)
D = (A) x (R)
Q = (A) x (R) x (T) x (%)
4. Determine the number of surface
application outlets
• see 3.15
Surface Injection-design
5. Determine supplementary requirements
– number of hoses (see 3-10)
– discharge time (see 3-11)
6. Calculate supplementary discharge rate
(Ds) and foam quantity (Qs)
Ds = (N) x (50 gpm)
Qs = (N) x (50 gpm) x (Ts) x (%)
Surface Injection-design
Total requirement for concentrate
Qtotal = Q + Qs
see example 3.2
Seal Protection
Floating Roof Tanks
• No vapour space
• gap at edge of roof a problem
• seal spans gap
Floating Roof Tanks-design
1. Calculate fuel surface area
A = total roof area - unprotected roof area
A =( )( r1)2 - ( )( r2)2
2. Determine application rate (R) and
discharge time (T)
• R = .30 gpm/ft2
• T = 20 min.
Floating Roof Tanks-design
3. Calculate discharge rate (D) and foam
concentrate quantity (Q)
D = (A) x (R)
Q = (A) x (R) x (T) x (%)
4. Determine the spacing of outlets
• see text
Floating Roof Tanks-design
5. Determine number of discharge devices
N = C/S
N = number
C = circumference ( x diameter)
S = maximum spacing
Floating Roof Tanks-design
6. Determine supplementary requirements
– number of hoses (see 3-10)
– discharge time (see 3-11)
7. Calculate supplementary discharge rate
(Ds) and foam quantity (Qs)
Ds = (N) x (50 gpm)
Qs = (N) x (50 gpm) x (Ts) x (%)
Floating Roof Tanks-design
Total requirement for concentrate
Qtotal = Q + Qs
see example 3.3
Dike Protection
• To contain tank farm
Dike Protection- Design
1. Calculate dike surface area
A = dike length x dike width
2. Determine application rate (R) and
discharge time (T)
R = .10 gpm/ft2 fixed outlets
R = .16 gpm/ft2 monitors
T = 30 min., flamm. liquids
T = 20 min., comb. liquids
Dike Protection- Design
3. Calculate discharge rate (D) and foam
concentrate quantity (Q)
D = (A) x (R)
Q = (A) x (R) x (T) x (%)
4. Determine the number of discharge devices
• every 30 ft
N = (2L + 2W)/30
Aircraft Hangers
• omit
Truck Loading Rack
Truck Loading Rack
Hazards
Truck Loading Rack
Strategy
Truck Loading Rack
Design