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.