Venturi Perchloric Acid Exhaust System
Perchloric Acid Information
Perchloric acid is clear liquid that has no odor. Solutions below 73% at room temperature are strong non-oxidizing acids. Perchloric acid becomes a strong oxidizer when heated or at higher concentrations, at or above 73%. Organic, metallic and non-organic salts formed from oxidation are shock sensitive and pose a great fire and explosion hazard. There are many documented accidents resulting from perchloric acid.
Inappropriate and Appropriate Materials
The following materials are not recommended for use with 72% perchloric acid: Nylon/polyamides, Dynel/modacrylic ester, Dacron/polyester, Bakelite, Lucite, vegetable-based Micarta, cellulose-based lacquers, copper/brass/bronze (which form shock sensitive salts), aluminum (dissolves), high nickel alloys (dissolve), cotton, wool, wood, and letharge (glycerin and lead oxide).
The following are suitable for use with 72% perchloric acid: Viton, chemically pure titanium, 316 stainless steel, Hastelloy C (slight corrosion rate), PVC, CPVC, Teflon, polyethylene, polypropylene, FRP, epoxy resins and glass. Acceptable coatings are limited to inorganic ceramic types, such as porcelain.
- A unique patent pending Corrosion resistant FRP perchloric acid exhaust system specifically designed by addressing the corrosion, fire, and explosion hazards of perchloric acid.
- Induced exhaust, no moving blower or moving parts in the air stream.
- Fiberglass Reinforced Plastic (FRP) construction providing superior corrosion resistance to perchloric acid.
- Vertical design without horizontal runs.
- Internal washdown system to flush any accumulated crystals in the venturi.
- Blower is mounted outside the air stream for safe service and inspection.
- Stack is insulated to prevent condensation of acid vapors and formation of ice.
- Water wash line is electrically heat traced to prevent freezing in sub-zero applications.
- Complies with "ACGIH" and "CRC Handbook on Laboratory Safety". CRC reference.
Sizes and Performance
- Available in 8 sizes, from 8" to 20", 500 to 3200 cfm and up to 2" SP.
- Roof mounted or inside duct mounted.
- Curb or flange mounted.
- Additional FRP stacks height available.
- Additional spray nozzles and wash rings available for new or existing ductwork.
- Solenoid valves are available to controls each washring or wash nozzle.
- A patent pending Controller is available to sequence fan operation and wash cycles.
Additional Reference Information
Standard on Fire Protection for Laboratories Using Chemicals
6-11 Perchloric Acid Hoods.
6-11.1* Perchloric acid heated above ambient temperatures shall only be used in a laboratory hood specifically designed for its use and identified as "For Perchloric Acid Operations."
Exception: Hoods not specifically designed for use with perchloric acid shall be permitted to be used where the vapors are trapped and scrubbed before they are released into the hood. (See also 9-1.2.4.)
6-11.2 Perchloric acid hoods and exhaust ductwork shall be constructed of materials that are acid resistant, nonreactive, and impervious to perchloric acid.
6-11.3 The exhaust fan shall be acid resistant and spark-resistant. The exhaust fan motor shall not be located within the ductwork. Drive belts shall be conductive and shall not be located within the ductwork.
6-11.4 Ductwork for perchloric acid hoods and exhaust systems shall take the Shortest and straightest path to the outside of the building and shall not be manifolded with other exhaust systems. Horizontal runs shall be as short as possible, with no sharp turns or bends. The ductwork shall provide a positive drainage slope back into the hood. Duct-work shall consist of sealed sections. Flexible connectors shall not be used.
6-11.5 Sealants, gaskets, and lubricants used with perchloric acid hoods, ductwork, and exhaust systems shall be acid resistant and nonreactive with perchloric acid.
6-11.6* A water spray system shall be provided for washing down the hood interior behind the baffle and the entire exhaust system. The hood work surface shall be watertight with a minimum depression of 13 mm (1/2 in.) at the front and sides. An integral trough shall be provided at the rear of the hood to collect wash down water.
6-11.7 The hood baffle shall be removable for inspection and cleaning.
6-11.8* If a laboratory hood or exhaust system was used for perchloric acid heated above ambient temperature, tests shall be conducted for explosive perchlorates before any inspections, cleaning, maintenance, or any other work is done on any part of the exhaust system or hood interior.
6-11.9 Prior to using a perchloric acid hood for any purpose, the hood shall be water-washed and shall be tested according to 6-11.8 to assure no presence of residual perchlorates.
Exception: In lieu of a sign, a properly maintained log of all hoods giving the above information shall be deemed acceptable.
Excerpt from NFPA 45, Standard on Fire Protection for Laboratories using Chemicals.
* CRC Handbook of Laboratory Safety.
Individuals working with perchloric acid and perchlorates must be trained inprocedures which will let them conduct their research with maximum safety. These are extremely dangerous materials.
* 188.8.131.52.8. Perchioric Acid Hood.
Under circumstances which would allow this errant material to be exposed to heat or to receive a sudden shock, the result could be a fire or an explosion in the space outside the duct.
It is recommended that the interior fittings of a perchloric acid hood should be non-sparking and that the lights should be explosion proof.
As a minimum, the blades and any other portion of the exhaust fan which might come into contact with the perchloric fumes should be coated with PVC, teflon, or another approved material which will resist the effects of the perchloric acid. An induction exhaust fan, where none of the fumes actually pass through any part of the motor or fan, is recommended...
Excerpt from CRC Handbook of Laboratory Safety. 4th Edition, 1995 by CRC Press LLC