Avoid Use of PVC Pipe and Water Hose Clamps With Compressed Air
July 4, 2016 - Compressed air is a common source of power for tools and equipment utilized in many shops and at construction sites. And while we constantly fret about the hazards associated with many of the tools that are powered by the compressed air, we give very little thought to the piping systems and hoses we utilize to distribute the compressed air from the compressor to the tools. So allow me to alert you to three very common hazards (and OSHA violations) that I see when conducting workplace safety audits for customers around the country.
Compressed Air Distribution Systems Fabricated From PVC Pipes and Fittings
I’ve run across this particular hazard more times than I care to admit; the use of Polyvinyl Chloride (PVC) piping systems to distribute compressed air within workshops and, in many cases, throughout entire buildings. This looks innocent enough; in fact the stamp on the PVC pipe in one of the photos below clearly states the Schedule 40 PVC pipe is rated for 600 PSI . . . . But look closer, it also says “water”, not air!
PVC pipes and fittings are primarily intended for use in plumbing applications. But they are neither suitable nor recommended for building a high-pressure compressed air distribution system. That is because water under high pressure is nearly incompressible, while air can easily be compressed. As a result, water under high pressure does not behave nearly as violently as compressed air does when the vessel in which they are contained ruptures. Therefore, PVC pipe and fittings, which can become very brittle after prolonged exposure to ultraviolet light from the sun and/or cold temperatures, can rupture and shatter relatively easily when subjected to high-pressure compressed air, sending sharp pieces of shrapnel flying through the air.
Numerous plastic pipe and fitting manufacturers and industry organizations, such as the Plastic Pipe and Fittings Association (PPFA), specifically warn that PVC pipes and fittings should not be used to store and/or convey compressed air or other gases. They also warn that PVC pipes and fittings should not be leak-tested with compressed air or other gases. The same warnings apply to use of chlorinated polyvinyl chloride (CPVC) pipes and fittings for building compressed air systems. Even OSHA has a letter of interpretation that warns against this practice, stating they will cite employers for violating the General Duty Clause [paragraph (5)(a)(1) of The OSH Act of 1970] when their inspectors discover PVC pipes and fittings being used for compressed air distribution systems in the workplace. The only allowable exceptions OSHA makes? When the PVC piping system is buried entirely underground, or encased in a suitable material such as steel pipe, both of which will encase the pieces of plastic when a component ruptures and shatters.
As a side note, there are some types of plastic pipes and fittings that are actually suitable for use in compressed air distribution systems. In fact, Polyethylene (PE) piping is produced specifically for this purpose. In addition, acrylonitrile butadiene styrene (ABS) is a material suitable for piping compressed air in many cases, as are pipe and fittings fabricated from high-density polyethylene (HDPE). Just check the manufacturer’s data to see when their product is, and is not, suitable for transport or storage of compressed air.
Water Hose Clamps Used For Compressed Air Hose Connections
Another very common hazard that I run across during inspections at both manufacturing and construction work-sites is the use of water hose clamps (aka worm-driven hose clamps)to splice compressed air hoses, as well as to connect compressed air hoses to quick couplers and other hose fittings.
OSHA Construction standard 1926.302(b)(5) states that “The manufacturer's safe operating pressure for hoses, pipes, valves, filters, and other fittings shall not be exceeded”. There is a similar standard in Subpart P of the OSHA General Industry standards at 1910.243(b)(2), which states that “Hose and hose connections used for conducting compressed air to utilization equipment shall be designed for the pressure and service to which they are subjected”.
Most compressed air hose manufacturers utilize a crimped fitting to make their connections to fittings (see photo on the right above). But water hose clamps are not made to withstand the same pressure as the clamps and other devices used by manufacturers to make connections when they fabricate compressed air hoses. A water hose clamp can also cut into compressed air hose material easily and cause it to break. Water hose clamps also loosen relatively easy when they are pulled across the ground or floor. So improper types of clamps and connectors must be avoided because they could fail and allow the end of a pressurized hose to whip around violently and strike someone. In fact, I will admit that as a teenager (many, many moons ago), I personally felt the wrath of such an angry air hose while working as a helper in a fabrication shop.
One quick side note; in some cases, I have seen where the proper type of compressed air connectors are used, but they are not the right size for the hose (fitting is usually too large). And even though the fittings are crimped into place, they too can come loose and cause the hoses to come loose and whip around.
Crow’s Foot Hose Connectors / Wires Or Retainer Pins Not Utilized
The same general hazard from the previous paragraph (about improper use of water hose clamps) also applies to compressed air hoses that are connected to one another with what I call a “Crows Foot” connector. These matched fittings are installed on the ends of each section of hose (hopefully with the proper type of clamps) and are then aligned and twisted to “lock” them together. However, there is nothing to keep them from accidentally “untwisting” during use and becoming disconnected.
To prevent this hazard from occurring, manufacturers of these types of hose connections instruct the user to insert either a retaining wire or a retainer pin (typically provided with the hose connectors) into and through the small holes that line up when the two couplers are twisted together (see pin inserted in one half of a clamp in one of the photos above). This helps lock both pieces of the compressed air hoses together and prevents the hose connectors from rotating and separating.
So these are three simple hazards (and potential OSHA citations) that can easily be identified if present in your workplace. And when they are found, they should be corrected as quickly as possible. Because no one should have to go to work and risk being struck by flying shrapnel or beaten half-to-death by a whipping hose just to earn a paycheck.
Do you have any comment or experience you’d like to share about the hazards discussed in this post? Or perhaps you have a different hazard associated with compressed air piping and hoses you’d like to discuss? If so, please to post your comments for this particular blog by CLICKING HERE. And as always, Please Share this Blog post with others in your Network who might benefit from this information.
ABOUT THE AUTHOR:Curtis Chambers is a Certified Safety Professional (CSP) and holds a Master of Science degree in Occupational Safety and Health. He has held numerous leadership positions managing and evaluating health and safety programs and providing training on workplace safety and health topics at various public organizations and private corporations. Mr. Chambers is currently the President of OSHA Training Services Inc. Visit their website at www.oshatraining.com.