CXS490 Dry
Chemical Systems
NFPA 17
 minimum requirements
 standard includes only essential to make standard
workable by skilled hands
 not applicable to installations prior to effective date
of standard
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Dry Chemicals
 most systems pre-engineered or designed by
manufacturer
 most design details are proprietary
 used for applications such as vehicle systems
 dry chemical = powder mixture (very small
particles)
 powder suspended in gas, which permits the
distribution to the hazard
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Dry Chemicals Sodium Bicarbonate
 NaHCO3 in use since 1920’s
 modified in 1960’s
• metal stearate additive enhances flow and prevents
caking
• silicone enhances compatibility with water based foam
 effective and cheap
 used on class B and C fires
 forms a soap-like surface on grease or cooking oil
fire - saponification, surface coating broken down
by heat
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Dry Chemicals Potassium Based
introduced in 1960’s
potassium carbonate, KHCO3, Purple K
potassium Chloride, KCl, Super K
urea based potassium carbonate, KC2N2H3O3,
Monnex
 used on class B and C fires, best on class B
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Dry Chemicals Multipurpose
 NH4H2PO4, monoammonium phosphate
 introduced in the 1950’s
 used on class B and C fires, and on class A
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Dry Chemicals Multipurpose
 forms a molten residue to prevent oxygen from
contributing to combustion
 not effective on deep fat fryers and delicate
electrical equipment where temp is more than 250
F and humidity is more than 50%
 deposits are difficult to remove not to be used with
delicate electrical equipment
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Dry Chemicals –
Properties Stability
 at low and ordinary temperatures
 additives may melt and cause sticking at higher
temperatures
 upper storage temp recommended 49 C or 120 F
 temp of 66 C or 150 F for short periods - 4 hours
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Dry Chemicals –
Properties Stability
 at fire temps decompose and dissociate
 danger when mixing multipurpose (acidic) with
other dry chemicals (alkaline) releases free carbon
dioxide gas and causes caking
 extinguisher shells have been known to explode
 dry chemicals may react violently with other
chemicals
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Dry Chemicals –
Properties
 commercial additives to improve storage, flow and
water repellency
 additives include metallic stearate, tricalcium
phosphate and silicones
 particle size 10 to 75 microns - 20 to 25 best,
beyond performance drops
 momentum gained from large particles will
transport smaller particles
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Extinguishing
Properties
 Comparison on Class B fires – best to worst
 monnex
 potassim bicarbonate & chloride
 multipurpose
 sodium bicarbonate
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Cautions
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most effective on class B materials
can be used with class C - non conductive
transitory on class A
supplement with water
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Advantages
 rapid knockdown of flame 2x as effective by weight
as CO2
 surface coating does not run down
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Disadvantages
 surface coating
 cleanup
• can be cleaned up with hose but mixture may
have environmental impact
• could vacuum
 caking into solid block when exposed to humidity
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Personnel Hazards
 nontoxic and noncarcinogenic
 acute effects include irritation of mucous
membranes and possibility of chemical burns to
skin, eyes and mucous membranes lining the
respiratory system
 temporary discomfort and irritating
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Procedure for
Personnel Protection
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Pre-discharge alarms
Signs
personnel training
egress analysis
provision of SCBA
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Testing
 Regular testing ensures system functions as
designed/intended
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Extinguishing
Mechanisms
 chain breaking - dry chemical thermally
decomposes and combines with the free radicals
and is major contributor
 smothering from carbon dioxide and release of
water vapour when agent heated
 cooling - decomposes endothermically
 radiation shielding is of some significance as cloud
of dry chemical shield the fuel from some of the
heat radiated by the flame
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Extinguishing
Mechanisms - A
 smothering from metaphosphoric acid with
multipurpose dry chemical
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System - Containers
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placed as close as possible to the hazard
up to 3000 pounds
maximum, pressure at 130 F
protected from damage
reserve not required unless located in remote
location
 systems protecting multiple hazards require a
reserve supply
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System – Expellant
Cylinders
 usually nitrogen, sometimes CO2
 mix with powder for ease of distribution to the
hazard, fluidization
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System – Piping
 pipe withstand the pressures encountered;
resistant to chemical corrosion
 galvanized, stainless steel, copper or brass
 welded or rolled groove, schedule 10, 1/8 to 3
inches, up to 560 psig
 steel threaded or cut grooved couplings,
schedule 40, 1/8 to 4 inches, up to 500 psig, 6
to 8 inches ,up to 420 psig
 fluidized agent likely to settle & lose momentum;
remix chemical at each tee
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System – Nozzles
 blow-off caps in dusty and oily environments
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Sequence of Operation
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Application Methods
Three basic application methods for dry chemical
piped systems:
Total flooding,
Local application - overhead.
Local application – tankside
Hazard characteristics determine most appropriate
method
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Applications
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liquified natural gas loading platforms
paint spray booths and dip tanks
transformer, generator and turbine protection
mining, conveyor and lubrication areas
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Extinguishing Systems
Two types:
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Engineered Systems
Pre-engineered Systems
Engineered Systems
Require:
 Individual design
 Calculations
 To determine the:
 Flow rates,
 Quantity of dry chemical,
 Number, size, location & pressure of nozzles,
 Size and length of the piping & fittings
Refer to NFPA 17 & listed design manual
Pre-Engineered
"Package" Systems
• Must conform with pre-determined parameters
•
Limits defined by testing and approval agencies
Ex: vehicle system.
Refer to:
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NFPA 17 and
Manufacturer’s listed installation manual
Total Flooding
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Total Flood Calculation
How much agent is required when space is 10 ft long by 10 ft
wide by 10 ft high?
The application rate is 0.077 lb/min/ft3
Minimum duration of discharge is 30 seconds
Total Flood Calculation
W = V x Ar x T
Volume = L x W x H = 10 x 10 x 10 = 1000 ft3
Ar = 0.0077 lb/min/ft3
T = 30 seconds = 0.5 min
W = V x Ar x T = 1000 x 0.077 x 0.5 = 38.5 lb
Compare with CO2:
W = V x Fv x Fc = 1000 x 0.063 x 1 = 63.0 lb
Total Flood Calculation
Number of Nozzles?
Each nozzle requires 500 ft3
Number = __V__ = 1000 = 2 nozzles minmum
500
500
Area per nozzle = 500 / H = 500 / 10 = 50 ft2
Space = L x W = √50 = 7.1 ft
L / 7.1 = W / 7.1 = 10 / 7.1 = 1.41 --> 2
Number of nozzle = 2 x 2 = 4 nozzles
Local Application
Overhead
• Based on "area protection" - dry chemical is
applied to areas from nozzles mounted
overhead.
• Hazard located in a large room or building where
total flooding application is inappropriate.
• Effective on such hazards as dip tanks, drain
boards, quench tanks, pipe coating,
manufacturing equipment and wax coaters
• Up to 80 sq. ft. (7.4 m2).
Local Application Tank-side
• Based on ‘area protection’
• Applied horizontally over the fire surface.
• Nozzles are mounted above liquid surface
• Minimize liquid splashing &
• To cover the complete surface of the tank
• Used for dip tanks, drain boards, quench
tanks or floor areas under machinery
• Up to 120 sq. ft. (11.1 m2)
Local Application Tank-side
Local Application
Combination
In some cases, combination of types
Examples: Quench Tank & Exhaust Duct System
Hand Hose
Lines
Consists of:
• Supply of dry chemical &
• Supply of expellant gas &
• One or more hand hose lines
• Deliver the dry chemical to the fire.
• These systems require trained personnel
Piping Method Tee
Splits
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The expellent gas - usually nitrogen.
Gas/dry chemical mixture must be maintained
as fluidized, homogeneous mixture
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Some tee split conditions will split mixture into
components - dry chemical and nitrogen.
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Possibility of insufficient flow rate
Can result in failure to extinguish.
Piping Method Tee
Splits
Two methods to overcome separation
 Venturi ensures homogeneous mixture when
entering a tee
 Critical length (20 x pipe diameter) to allow
remixing of the dry chemical to occur after a
change in direction.
 Critical length more cumbersome but lower
pressure drop of the agent mixture
Piping Method Tee
Splits
Inspection &
Maintenance
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Both must be provided
Suppression systems – mechanical
Need periodic care
Carried out in accordance with manufacturer’s
recommendations
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Inspection I
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Necessary to provide reasonable assurance
the fire suppression system is:
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Fully charged and Operable
At regular intervals.
Recommended daily
Performed by the operator of the apparatus.
Inspection II
Visual observation system components
Inspection VI
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Discharge during daily inspection not
recommended.
When inspections give concerns -> reliability
may be desirable to discharge the system
Discharge during training exercises &
certification inspections provide testing
opportunities
Maintenance I
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To provide maximum assurance system will
operate effectively and safely,
Conducted at six-month intervals or
Earlier when indicated by an inspection
Very complex & detailed operation
including discharge of the system
Strict adherence to manufacturer’s
recommendation
Maintenance II
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Nitrogen cylinder regulators tested
annually
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Often performed by contract with outside
firm
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If fire department personnel not certified to
perform the maintenance on a system
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contractor recommended
Recharge
When necessary:
operator follow the manufacturer’s
recommendation in the operator’s manual
 Clean out the hoses and pipes
 Short bursts of nitrogen builds up pressure in
the hoses - making clean out more effective
end
of
Presentation
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