Dry and Wet Chem Systems

1
Dry and Wet Chem Systems

• Ch. 8, pages 148-162
• Dry Chemical Systems
• Dry Chem. System Components
• Dry Chem. Sequence of Operation
• Applications for Dry Chem Systems
• Types of Dry Chem. Systems
• Wet Chemical Systems

2
Dry Chemical Systems

• either pre-engineered
• or
• designed by supplier
• design details are proprietary
• commercial cooking
• dry chem is different from dry powder

3
Dry Chemical Examples

• Commercial cooking
• heavy-duty vehicles
• graders, buses
• portable units
• (up to 300 lb)
• flamm. Liquids
• combined with foam (twin agent)

4
Dry Chem. Agents

• Small solid particles
• suspended or fluidized in air
• more complicated than gaseous or liquid agents

5
Dry Chem. Agents

• 3 broad categories
• sodium carbonate based
• potassium based
• multipurpose

6
Sodiium Bicarbonate based

• NaHCO3
• baking soda
• Flamm. Liquids (class B)
• Electrical (class C)
• ideal for grease fires
• saponify (soap-like layer)

7
Potassium based

• Flamm. Liquids (class B)
• Electrical (class C)
• better than sodium bicarbonate except on grease
  fires
• KHCO3, potassium bicarbonate, Purple K
• KCl, potassium chloride, Super K
• KC2N2H3O3, Monnex

8
Multi-purpose

• Monoammonium phosphate
• A B or C
• Form molten residue
• Not effective on deep fat fires
• Not as effective as narrow purpose agent

9
Dry Chem. advantages

• Rapid knockdown
• minimizes damage
• 3D surface coating
• minimizes reignition
• sprays, leaks etc.

10
Dry Chem. disadvantages

• Surface coating
• messy residue
• expensive cleanup
• caking
• from moisture
• vibration
• particles commonly coated

11
Personnel hazard

• Material is non-toxic
• particles too large to penetrate into deep lung
• products of combustion harmful
• usual precautions to prevent exposure

12
Testing of systems

• Testing
• messy
• expensive
• requires clean-up
• most are not tested
• reliability issue
• least risk with popular pre-engineered systems

13
Extinguishing mechanism

• Coating
• smothering
• heat absorption
• block chain reaction

14
Container

• From 1lb to 3,000 lb
• small are pressurized
• large have separate expellant gas cylinder
• minimize piping runs
• rupture disk
• see fig 8-1

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Expellant gas cylinder

• For large systems
• 100s of lb
• N2 or CO2
• to fluidize dry chem

16
Piping and nozzles

• Minimize runs
• remix at each tee
• withstand pressure
• corrosion resistant
• not cast iron
• variety of nozzles available

17
Sequence of operation

• See 8-4
• 1. Detector senses fire
• 2. Signal to panel
• 3. Panel interprets signal, if interpreted as
  fire
• 4. Alarm sounded
• 5. Equipment, HVAC shutdown
• 6. Could be manual activation

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Sequence of operation

• 7. Could have remote activation
• 8. Signal to actuator on propellant tank
• 9. Valve opened
• 10. Propellant flows to dry chem tank
• 11. Powder fluidized
• 12. pressure builds in tank

19
Sequence of operation

• 13. Rupture disk bursts
• 14. Fluidized particles/propellant gas flow
• 15. Discharge from nozzle

20
Applications

• Commercial cooking
• petrochemical
• paint spray booths
• dip tanks
• tranformers
• generators
• conveyors

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Types of systems

• Total flood
• local application
• hand hose line
• pre-engineered

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Total Flood

• Fill enclosure
• paint spray booth
• enclosure must be sealed
• ventilation shut down
• additional dry chem for unclosable openings

23
Local Application

• Hazard must be isolated
• drum filling stations
• if liquid, consider splashing
• if outdoors, consider wind dispersion

24
Hand lines

• As a supplement to fixed system
• minimum 30 sec capacity/line

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Pre-engineered

• Commercial restaurants
• vehicle fueling
• mobile equipment
• packaged units
• highest reliability

26
Wet Chemical

• Water and extinguishing chemical
• usually potassium based chemical
• pre-engineered restaurant systems