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You've got me under Pressure

Thu, 10/18/2012 - 11:01am
Vince McLeod, CIH

A facility support technician was called to repair a leaking valve in the compressed gas cylinder storage room. Upon entering the room he found the leaking valve near the floor under one of the large gas cylinders near the back corner. Kneeling down with his tools he started in on his assigned morning project. Within minutes he noticed he was breathing hard, getting a headache, and feeling tired. Remembering his long list of things to do that day, his first thoughts were to push ahead and hurry to finish this job. Fortunately, he yielded to his instincts that something was not quite right and tried to recall what these symptoms meant from that safety training long ago. He stood up and was hit with an overwhelming feeling of dizziness. He steadied himself and then left the room to seek assistance.

This close call turned out to be the result of a leak in the carbon dioxide gas delivery system. The much heavier than air carbon dioxide gas had settled near the floor displacing the normal air and its oxygen. Colorless, tasteless, and odorless, the greatly increased concentration of carbon dioxide might have easily gone un-noticed except for the symptoms produced. Had the technician tried to finish the valve repair job, a few more minutes of breathing the heavily concentrated carbon dioxide probably would have resulted in unconsciousness and possibly death.

Forensic laboratories, just like many research laboratories, use a variety of compressed gases. These can range from the classic inert gases like carbon dioxide (used in the scenario above), helium, and argon to the highly flammable acetylene and oxygen used for gas chromatographs and high performance liquid chromatography. So in this issue the Safety Guys offer a few basic tips on safe use of compressed gas cylinders and preventing accidents and close calls.

How do you know what you are dealing with?
Compressed gas is loaded into, transported in, and used from heavy walled metal cylinders. These cylinders come in all sizes and shapes from little one pound “lecture” bottles to railroad tank cars. The size most commonly used in forensic laboratories and facilities are the eighty pound cylinders, referred to as “K” sized bottles. They are about eight inches in diameter and forty eight inches tall and can contain a wide array of compressed gases.

The requirements for manufacture of cylinders are detailed in Title 49 Code of Federal Regulations, Part 178, Specifications for Packaging.1 For our purpose we just want to point out that all cylinders should have permanent stamped markings on the shoulder. These should show the DOT specification, the proper service pressure (in gauge pounds per square inch, psig), the manufacturer’s symbol and serial number, the owner’s symbol, and most importantly for safety, the date of the initial qualification test and any subsequent tests. Cylinders need to be re-tested every five years. In addition to the permanent markings, the cylinder should also have an identifying label on the shoulder indicating the cylinder’s contents.

Basic Rules for Safe Handling of Cylinders from Acceptance to Zero (gas left)
What follows here is a condensed set of basic guidelines applicable to all gas cylinders. The Compressed Gas Association publishes an excellent reference2 as well as a large number of specific pamphlets with more detailed information. Additional resources that we use a lot are Prudent Practices3 by the National Safety Council and the Canadian Compressed Gas Safety Web site.4 An attempt to cover all the different classes of compressed gases is beyond the scope of this article but we will gladly respond to readers’ special concerns perhaps with follow up articles if interest is high.

 

Step 1: Before accepting or receiving compressed gas cylinders perform a quick inspection. All cylinders should be shipped with regulators removed and safety caps in place. Check cylinders for heavy rust or pitting and refuse any questionable ones. Check the certification date(s). Finally, make sure all cylinders have a durable label that cannot be easily removed and that clearly identifies the contents.

Step 2: Transport compressed gas cylinders with care. Since we are only moving cylinders from the vendor supply truck to our storage area or direct to the laboratory or facility use area, this step is straight forward but often done haphazardly or with a cavalier attitude. Compressed gas cylinders should only be transported using wheeled carts designed for this purpose. Make sure safety caps are in place and cylinders are secured to the cart. When moving multiple cylinders, do not allow them to bear against or strike each other. Finally, know the route you will travel and remove all potential obstacles. If lift gates or ramps are used, enlist a spotter or helper before moving cylinders.

Step 3: Develop specific safe handling and use procedures for your compressed gas cylinders. Depending on the specific gas used, safety procedures can become quite complex. For example, extremely hazardous gases may require dedicated ventilated storage cabinets, safety interlocks, and elaborate alarm systems. Here are a few basic ground rules to follow. When transporting, ensure all cylinders are properly secured. Common methods include chains, straps, and specialty clamps. Install a proper regulator when in use and when not in use remove the regulator and install safety caps. Maintain adequate ventilation and temperature control for the area. Finally, close the valve and release the pressure in the system at the end of each use.

Step 4: Don’t forget about storage areas. Most sites have a designated area for compressed gas cylinder storage, particularly large facilities and those with high volume use. These areas are often relegated to the back closet and overlooked. General safety considerations include many already mentioned above such as securing cylinders to prevent tipping, falling, and knocking together; having regulators removed and safety caps installed; and maintaining good ventilation and temperature control. There are a few important additions however. First, the area should be locked and secured against theft and vandalism. Preferably, the cylinder storage area is located away from emergency exits. The next most important issue is storage by compatibility along with proper separation between hazard classes. Be sure to check with local fire codes that specify distances and quantities allowed. Clearly mark all empty cylinders and segregate these from full cylinders as well. Empty cylinders should be moved and handled with the same care as full ones and returned to the vendor promptly.

Summary
Taking the time to develop and implement a compressed gas safety program for your research or production facility will go a long way in preventing accidents and potential tragedy. Most fixes and corrections are low cost and easily installed and maintained. Compared to the costs associated with the alternatives, it is hard to argue against a good compressed gas safety program.

References

  1. 49 CFR Part 178, Specifications for Packaging. U.S. Department of Transportation, January 2005. http://www.access.gpo.gov/nara/cfr/waisidx_04/49cfr178_04.html
  2. Handbook of Compressed Gases, Compressed Gas Association, Arlington, VA. Van Nostrand Reinhold. NY latest edition.
  3. Prudent Practices in the Laboratory, National Research Council. National Academy Press, Washington D.C. latest edition.
  4. Compressed Gas Safety page. Canadian Centre for Occupational Health and Safety. July 2008 http://www.ccohs.ca/oshanswers/prevention/comp_gas.html

Vince McLeod is an American Board of Industrial Hygiene Certified Industrial Hygienist and the senior IH with the University of Florida’s Environmental Health and Safety Division. He has 24 years of experience in all facets of occupational health and safety and specializes in conducting exposure assessments and health hazard evaluations.

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