Dry and Wet Chem Systems Ch. 8, pages 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

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

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

Dry Chem. Agents Small solid particles suspended or fluidized in air more complicated than gaseous or liquid agents

Dry Chem. Agents 3 broad categories sodium carbonate based potassium based multipurpose

Sodiium Bicarbonate based NaHCO 3 baking soda Flamm. Liquids (class B) Electrical (class C) ideal for grease fires saponify (soap-like layer)

Potassium based Flamm. Liquids (class B) Electrical (class C) better than sodium bicarbonate except on grease fires KHCO 3, potassium bicarbonate, Purple K KCl, potassium chloride, Super K KC 2 N 2 H 3 O 3, Monnex

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

Dry Chem. advantages Rapid knockdown –minimizes damage 3D surface coating –minimizes reignition sprays, leaks etc.

Dry Chem. disadvantages Surface coating –messy residue –expensive cleanup caking –from moisture –vibration –particles commonly coated

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

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

Extinguishing mechanism Coating smothering heat absorption block chain reaction

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

Expellant gas cylinder For large systems 100’s of lb N 2 or CO 2 to fluidize dry chem

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

Sequence of operation See 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

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

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

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

Types of systems Total flood local application hand hose line pre-engineered

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

Local Application Hazard must be isolated –drum filling stations if liquid, consider splashing if outdoors, consider wind dispersion

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

Pre-engineered Commercial restaurants vehicle fueling mobile equipment packaged units highest reliability

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