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 2

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 3

Dry Chemicals Sodium Bicarbonate

     NaHCO 3 in use since 1920 modified in 1960 ’s ’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 4

Dry Chemicals Potassium Based

     introduced in 1960 ’s potassium carbonate, KHCO 3 , Purple K potassium Chloride, KCl, Super K urea based potassium carbonate, KC 2 N 2 H 3 O 3 , Monnex used on class B and C fires, best on class B 5

Dry Chemicals Multipurpose

   NH 4 H 2 PO 4, monoammonium phosphate introduced in the 1950 ’s used on class B and C fires,

and

on class A 6

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 7

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 8

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 9

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 10

Extinguishing



Properties

Comparison on Class B fires – best to worst  monnex  potassim bicarbonate & chloride  multipurpose  sodium bicarbonate 11

Cautions

    most effective on class B materials can be used with class C - non conductive transitory on class A supplement with water 12

Advantages

  rapid knockdown of flame 2x as effective by weight as CO 2 surface coating does not run down 13

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 14

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 15

Procedure for Personnel Protection

     Pre-discharge alarms Signs personnel training egress analysis provision of SCBA 16

Testing

 Regular testing ensures system functions as designed/intended 17

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 18

Extinguishing Mechanisms - A

 smothering from metaphosphoric acid with multipurpose dry chemical 19

System - Containers

      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 20

System – Expellant Cylinders

  usually nitrogen, sometimes CO 2 mix with powder for ease of distribution to the hazard, fluidization 21

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 22

System – Nozzles

 blow-off caps in dusty and oily environments 23

Sequence of Operation

24

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 25

Applications

    liquified natural gas loading platforms paint spray booths and dip tanks transformer, generator and turbine protection mining, conveyor and lubrication areas 26

Extinguishing Systems

Two types:   Engineered Systems Pre-engineered Systems 2

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 2

Pre-Engineered "Package" Systems

• • Must conform with pre-determined parameters Limits defined by testing and approval agencies Ex: vehicle system.

• • Refer to: NFPA 17 and Manufacturer ’ s listed installation manual 2

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 3

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 3

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 3

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). 3

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) 3

Local Application Tank-side 3

Local Application Combination In some cases, combination of types Examples: Quench Tank & Exhaust Duct System 3

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 3

Piping Method Tee Splits

  The expellent gas - usually nitrogen. Gas/dry chemical mixture must be maintained as fluidized, homogeneous mixture  Some tee split conditions will split mixture into components - dry chemical and nitrogen.

  Possibility of insufficient flow rate Can result in failure to extinguish.

3

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 4

Piping Method Tee Splits

4

Inspection & Maintenance

 Both must be provided  Suppression systems – mechanical  Need periodic care  Carried out in accordance with manufacturer ’ s recommendations 42

Inspection I

     Necessary to provide reasonable assurance the fire suppression system is: Fully charged and Operable At regular intervals. Recommended daily Performed by the operator of the apparatus. 4

Inspection II

Visual observation system components 4

Inspection VI

   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 4

Maintenance I

     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 4

Maintenance II

 Nitrogen cylinder regulators tested annually  Often performed by contract with outside firm  If fire department personnel not certified to perform the maintenance on a system  contractor recommended 4

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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