Ventilating Hazardous Classified Locations. Steve Brandt, P.E. D.F. Brandt, Inc. Isolation Air Systems, Inc.

Transcription

1 Ventilating Hazardous Classified Locations Steve Brandt, P.E. D.F. Brandt, Inc. Isolation Air Systems, Inc.

2 Where did the concept of hazardous locations originate? Early 1900 s conversion from gas to electric lighting Electrification of mines and ensuing explosions Early mine safety alarms comprised two bare wires that were meant to be shorted by miner s tool to complete electrical circuit and energize alarm bell above grade, often sparking and igniting Firedamp gases (predominantly methane)

3 Handling the arrival of the Hindenburg at its US mooring station in Lakehurst, NJ presented several challenges. In the 1920s the US controlled virtually all the world s supply of helium, and realizing its strategic importance in lifting reconnaissance airships, the US Congress passed the Helium Act of 1927, prohibiting the sale of helium to foreign nations. Zeppelin Hindenburg Undeterred, the Hindenburg s management were confident they could influence their American business partners to lobby Congress for an exception, thereby making the inert gas available for the Hindenburg. The Hindenburg s engineers proceeded with designing the airship for helium. The German Zeppelin Company would also have to convince the Nazi government to part with a significant amount of hard currency if helium could be made available, all at a time when the regime had imposed strict controls on the export of capital, which was being retained to finance Germany s regrowth and rearmament. While designed for Helium, the Hindenburg was inevitably doomed to lift with Hydrogen.

4 Hangar No. 1, Lakehurst, New Jersey Built in 1920 to provide a fabrication facility for America s rigid Zeppelin program, Lakehurst Naval Station s massive Hangar No. 1 was built to allow safe storage and service of Germany s hydrogenbased airships, most notably the Hindenburg. With a continuously grounded steel floor, explosion-proof lighting and electrical components, Hangar No. 1 was deemed suitable to service the hydrogen-based vessels. All of the US airships built and serviced at Lakehurst were helium-based airships, and the Lakehurst facility incorporated a helium purification and storage plant.

5 May 6, Disaster Strikes the Hindenburg Following 20 successful transatlantic crossings in its inaugural season, the Hindenburg s first crossing in 1937 ended in disaster. After circling the landing site at Lakehurst for more than three hours, and unable to level the Hindenburg s tail by repeated ballast drops, spectators recalled seeing the skin of the tail section ripple as it approached the landing moor, only to explode in flames. While conspiracy theories remain alight today, aviation experts believe the deflagration was caused by a structural cable that snapped, in turn piercing one of Hindenburg s sixteen gas cells. While pure hydrogen is not ignitable, once mixed with air it became a volatile cocktail likely ignited by static charge from the airframe.

6 What constitutes a hazardous location? Ignitable concentrations of flammable vapors, liquids or gases, or combustible dusts or fibers which may be present and the likelihood that a flammable or combustible concentration or quantity is present -NEC Article 500

7 NEC Hazardous Area Classifications Class I Locations- those in which flammable gases or vapors are or may be present in air in quantities sufficient to produce explosive or ignitable mixtures Class I Division 1: A location in which ignitable concentrations of flammable gases or vapors can exist under normal operating conditions, or in which ignitable concentrations of such gases or vapors may exist frequently because of repair or maintenance operations or because of leakage ; or in which breakdown or faulty operation of equipment or processes might release ignitable concentrations of flammable gases or vapors, and might also cause simultaneous failure of electric equipment Class I Division 2: A location in which volatile flammable liquids or flammable gases are handled, processed, or used, but in which the liquids, vapors, or gases will normally be confined within closed containers or closed systems from which they can escape only in case of accidental rupture or breakdown of such containers or systems, or in abnormal operation of equipment; or in which ignitable concentrations of gases or vapors are normally prevented by positive mechanical ventilation, and which might become hazardous through failure or abnormal operation of the ventilating equipment; or that is adjacent to a Class I Division 1 location, and to which ignitable concentrations of gases or vapors might occasionally be communicated unless such communication is prevented by adequate positive-pressure ventilation from a source of clean air, and effective safeguards against ventilation failure are provided

8 What about the Class II, Class III locations? Class II Locations: Are those that are hazardous because of the presence of combustible dust Class III Locations: Presence of easily ignitable fibers or flyings, but in which such fibers or flyings are not likely to be in suspension in the air in quantities sufficient to produce ignitable mixtures

9 What about the Groups? Flammable Gases and Vapors having flash point (temperature at which a particular organic compound gives off sufficient vapor to ignite in air) below 100 F Examples Group A: Acetylene Group B: Ethylene Oxide, Hydrogen, Propyl Nitrate Group C: Ethylene, Hydrogen Sulfide, Toluene Group D: Ethanol, Gasoline, Methane, Styrene

10 Hindenburg Trivia The electrical room of the Hindenburg contained (2) 35 KW generators driven by 60 HP Daimler diesel engines. Electrical distribution at 220V and 24V One generator was sufficient to meet the entire electrical demand of the vessel

11 Common hazardous classified areas Wastewater Treatment Facilities Gas and oil production and processing Printing industries, paper and textiles Hospital operating suites Grain handling, storage and processing Sugar refineries Light metal working, e.g. aluminum, titanium, magnesium Woodworking Commercial Garages- Class I Div 2 to 18 AFF except when ventilated

12 Where would we encounter a hydrogen atmosphere in industry today?

13 Where would we encounter a hydrogen atmosphere in industry today?

14 When is a Gas or Vapor a Hazard? When the gas concentration is air is between the lower (LEL) and upper (UEL) explosive limits (percent by volume) Gas LEL UEL Hydrogen H2S Ammonia Gasoline Methane

15 Hydrogen vs Helium as a lifting gas The Hindenburg could lift 240 gross tons with Hydrogen with 7,062,000 cubic feet distributed through 16 gas cells But would be limited to 212 tons on Helium

16 Codes and Standards National Electrical Code NFPA 497 Electrical Installations in Chemical Atmospheres Involving Flammable Liquids, Gases, or Vapors NFPA 820 Standard for Fire Protection in Wastewater Treatment and Collection Facilities 10 States Standards for Wastewater Facilities

17 NEC Ignition Temperature Codes Example Gasoline, Methane Methyl Ethyl Ketone Butane Hydrogen Sulfide autoignition temperature or kindling point of a substance is the lowest temperature at which it spontaneously ignites in normal atmosphere without an external source of ignition, such as a flame or spark. This temperature is required to supply the activation energy needed for combustion.

18 What are the required Ventilation Rates for Wastewater Plant Class I Locations? NFPA 820 Varies by location and function within the plant, up to 12 continuous air changes in Class I Div 1 Locations Odor Control Systems- Class I Div 2 Areas within 3 ft of leakage sources such as fans, dampers, flexible connections, flanges, pressurized unwelded ductwork and odor control vessels 10 States Wastewater Standards Housed Facilities: Fresh air shall be introduced continuously at a rate of at least 12 air changes per hour, or intermittently at a rate of at least 30 air changes per hour. Odor control facilities may also be warranted

19 Smoking was allowed on the Hindenburg, but only in the pressurized airlocked smoking room

20 How do we reconcile the NEC Temp Code Requirements with Heating these Spaces? Wastewater: Hydrogen Sulfide-T2B, 500 F; Methane T1, 450 F Maximum Surface Temperatures Current standards and codes do not directly address the surface temperatures of heating systems serving classified locations One can argue it is not good practice to use heat exchangers with surface temperatures that exceed 500F, e.g. Indirect Fired Gas Heaters, Open Coil Electric Duct Heaters serving classified locations

21 Heat Options Glycol / Hot Water Self Contained Electric / Glycol Heat Exchangers No concerns regarding surface temperature restrictions, but requires boiler system located in un-classified space. Lower fuel cost than electric options No remote boiler system required, but capacities limited by FM/UL approved terminal devices. Higher fuel cost than remote boiler option

22 Either way, utilize heat recovery options Heat Pipes- Sensible Heat Recovery A traditional heat pipe is a hollow cylinder filled with a vaporizable liquid. A. Heat is absorbed in the evaporating section. B. Fluid boils to vapor phase. C. Heat is released from the upper part of cylinder to the environment; vapor condenses to liquid phase. D. Liquid returns by gravity to the lower part of cylinder (evaporating section). For balanced air flows, Effectiveness = Percentage difference between high dry bulb temp and low dry bulb temp air streams that is transferred to the colder air stream from the warmer air stream For example: 70F-10F= 60F; at 50% Effectiveness cold air stream heated to *(70-10)=40F

23 Combining Heat Pipes w/ Electric Glycol HX +

24 189 KW Class I Div 1 Duct Heater Array 6 row 12 fpi Heresite Coated Heat Pipe 19,000 cfm supply / exhaust Heat pipe 55% Effectiveness = Installed in Baltimore, MD, the heat pipe recovers the equivalent of 547 MMBTU annually

25 How do you control altitude in your dirigible? You vent gas! The wheel in the upper right simultaneously vented hydrogen from 11 of the 16 gas cells on the Hindenburg. When fore or aft trim was required the hand toggles below the wheel would allow release of gas pressure on any of the individual 16 cells to level the ship

26 Eliminating the Ignition Source- Static Charge ASTM D-4167: Carbon-rich exterior resin coating on fiberglass ductwork, vessels and fans maintains electrically grounded system eliminating build-up of static charge Ground wire

27 Electrically bonded ductwork for Hazardous Dust Collection Wet dust collection system handling aluminum dust Aluminum dust oxidizes to form hydrogen, requiring these collection systems to be internally vented to release the gas

28 NFPA 820 re Odor Control Systems Areas within 3 ft of leakage sources such as fans, dampers, flexible connections, flanges, pressurized un-welded ductwork, and odor-control vessels Class I Div 2, Group D

29 Stay beyond the 3 envelope! Class I Div 1 Group D dehumidifying makeup air unit serving WWTP pipe gallery- Brine chiller to the right is outside the 3 envelope and therefore does not need to be XP

30 Odor control in Wastewater Treatment Facilities Clinton Street Combined Sewer Overflow Storage Facility Dual 12 diameter x 20 high radial flow carbon vessels, each holding 40,000 lbs activated carbon pellets; each vessel conditions 30,000 cfm exhaust air from storage tank and tunnel system. Exhaust air contacts carbon bed for 2.7 seconds before exhausting to Armory Square district 1.3 lbs carbon/ CFM

31 Scrubbing H2S - Challenge testing Results: Vessel # % removal efficiency Vessel # % removal efficiency

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33 Even Fido could fly on the Hindenburg The Hindenburg s Chief Steward Max Henneburg takes a passenger s dog for a walk along the ship s keel during the first flight to South America in April 1936

34 What are the advantages of using heat pipes for heat recovery?

35 What are the advantages of using heat pipes for heat recovery? Answer: Free heat recovery No moving parts

36 How far does the classified area extend beyond the odor control system ductwork per NFPA 820?

37 How far does the classified area extend beyond the odor control system ductwork per NFPA 820? Answer: 3

38 When hydrogen sulfide fumes condense, what is formed?

39 When hydrogen sulfide fumes condense, what is formed? Answer: Sulfuric Acid

40 And finally, for extra credit name the 6 noble gases

41 For extra credit name the 6 noble gases Helium Neon Argon Krypton Xenon Radon Oganesson

42 Questions?