Air

Question
Hi
   Although I am a diver this question is concerning Breathing apparatus for rescue. I would like to know if you know of any regulations regarding the length of time, air will remain good for breathing in a cylinder. I have asked SCBA manufactures and have not received a decent answer to this question.

I am in a location where self rescue is very likely to be needed at some point. The SCBA can have a cylinder which will only be charged once per year. Your opinion is welcome.

Thanks Norman


Answer
Norman,

The "shelf life" of the air inside a SCBA is really going to be dependent on the material the cylinder is made from and the presence of moisture inside the cylinder.

OSHA and NIOSH have pretty strict requirements for the moisture content of compressed air used to fill both SCUBA and SCBA cylinders.  If those requirements are being met, then moisture should not be a concern.  

However, if there is moisture in the air used to fill the cylinders, this can cause problems with steel cylinders.  The oxygen in the air can react with the moisture and steel to form iron oxide (rust) inside the cylinder.  This could lead to a depletion of the oxygen in the air (as well as weakening the strength of the cylinder itself).  Aluminum cylinders are not as susceptible to this oxidation.  As the aluminum oxidizes, a coating of aluminum oxide (looks like white powder) is formed and that will limit the amount of corrosion, and thus limit the amount of oxygen that is removed from the air in the cylinder.

I don't think you will find any specific regulations that cover the amount of time the air will remain safe for breathing, given the variables I've stated.  You will find that the OSHA and NIOSH requirements for inspections and maintenance will most likely cover the concerns of oxygen depletion, if any, inside the cylinders.

It's disappointing that the manufacturers were not very helpful to you.  Try contacting OSHA or NIOSH to see if they have a definitive answer to an actual length of time air will remain safe in your cylinders.  Another resource for information might be the Compressed Gas Association.

Hope this helps,

Henry Babcock
AllExperts SCUBA Expert