Yesterday, in response to my Coilhose Redi-Burst pocket air blow gun post, HangFire said: a missed opportunity to describe just what “OSHA Compliant” means in an air gun.
Yikes, I’d been avoiding this discussion for a while! I managed to dig up OSHA regulation standard 1910.242(b), which says:
Compressed air used for cleaning. Compressed air shall not be used for cleaning purposes except where reduced to less than 30 p.s.i. and then only with effective chip guarding and personal protective equipment.
That’s more or less what I heard before, that the outlets of compressed air blow guns must be reduced below a certain pressure (30 PSI) for safety purposes.
Why? Directive STD 01-13-001 answers that:
This requirement is necessary in order to prevent a back pressure buildup in case the nozzle is obstructed or dead ended.
OSHA provides 2 acceptable methods (PDF) in which tools can be compliant with their regulation. The first involves an air pressure reducer that is placed before an air blower nozzle, usually in the air line between compressor and air blower, and the second involves a nozzle with built-in pressure reducer or relief device that reduces the air pressure in case the nozzle is dead ended (blocked).
In the same document, further explanation of the standard is offered:
The intent of the regulation is to allow for proper cleaning operations and to prevent chips and other waste materials from being blown into eyes or skin of the workers which may cause injuries. The design of the orifice and the velocity of the air passing out of the orifice or nozzle shall be such that it will not cause the waste material being cleaned away to be blown into the eyes or skin. Any relief vents or ports shall not be a hazard to the operator.
In another comment to the Coilhose Redi-Burst post, Brett explained OSHA compliance in a way I’ve heard it discussed before, that the reduced pressure is to prevent skin and blood vessel infiltration should an air blow gun be aimed at someone’s body.
In an Exair explanation of OSHA regulations, it describes things a little better.
Looking at product description of the OTC blow gun that’s shown above, it says it’s designed for an operation pressure of 50 to 235 PSI and that when inlet pressure is 90 PSI, the venting design prevents pressure exceeding 30 PSI if tip becomes blocked. This wasn’t crystal clear to me until I looked at Exair’s explanation.
I should point out that OTC and Exair are not related companies, but the OTC had a related product description and Exair has an informative OSHA discussion page.
Going by the Exair explanation, an air blower or nozzle with relief or reduction valve ensures that, if it’s held against your skin, the full velocity and force of the compressed air won’t be forced into your body. The outlet pressure should not exceed 30 PSI if the air blow gun or nozzle is properly designed to be OSHA compliant.
Okay, so it’s starting to get clearer for me. Some air blow guns, such as this Coilhose model, require that Line pressure must be regulated to 30 PSI or less for rubber tip to be OSHA compliant. Those satisfy OSHA’s first acceptable compliance method. Others have built-in or attachable safety tips that satisfy OSHA’s second acceptable compliance method.
If your air gun doesn’t have a built-in pressure relief, you can buy a safety tip, such as this Guardair attachment via Grainger. I don’t recall seeing any safety nozzle tips that are female threaded to accept additional nozzle attachments.
There is also a great discussion at manufacturing.net, where they interviewed Guardair’s director of engineering. Towards the bottom of the article, there’s an explanation of how these types of safety nozzle tips, with side holes that redirect air in case the front of the tip is dead-ended or blocked, can actually improve air gun performance. They say that the Venturi nozzle design can increase the volume of air exiting the nozzle to boost available thrust by up to 250%.
Oops, this completely slipped my attention, but it makes perfect sense. Thanks to Bernoulli’s principle and the Venturi effect, there will be a pressure drop in the nozzle due to the movement of the high velocity air, causing more air to be drawn into their airflow from the holes on the side. Thus, you will have a greater volume of air passing through the front of the safety air blower nozzle tip, compared to volume or air that enters the inlet of the nozzle tip from your compressor.
Anyway, I think I’ve got a good understanding of OSHA’s air gun safety regulations now. There are also standards that regulate how loud an air gun can be, but maybe that’ll be a discussion for another time.
Please don’t take any of this as safety advice, because it’s not. Remember, I’m just trying to understand the standard ands regulations.
How’s your understanding of this stuff? If you have added insight, please share it in a comment!