Do you trust that Gas? – Tips for Getting Safe Dive Air

At some point before every dive you hand over the care of your lungs to the dive shop employee filling your tank. Few divers ever think about and even less understand what goes on behind the scenes in preparing and operating the complex system that fills his/her tank. When we did research on this question we came away surprised that we ever get good air. Air compressor and purification systems are extremely complex. There are many points along the path from air intake to scuba tank at which a seeming minor change can cause a major problem with the quality of your breathing gas.

This article was inspired by our personal experience of twice getting a “bad fill.” Prepping for a dive, I found the air tasted like diesel fuel. That started my quest to find out what happened and how to be sure that it never happened again. Along the way we heard a dangerous myth from more than one dive shop employee that goes like this. “We use food grade oil in our compressor, so even if the air tastes bad it is non-toxic.” However, that is wrong. Any oil in your lungs can cause a potentially serious lung inflammation know as “lipoid pneumonia.” The symptoms can range from persistent cough to lesions on the lung.

Oil in the air is only one of many varieties of an air fill incident. Others include particulate matter, tank damaging moisture and even deadly carbon monoxide. This was all the incentive we needed to want to help ourselves and other divers increase their chance of getting pure safe breathing gas.

As with many industry failings that are likely to cause harm or death, economics can play a big role. Also common to these types of issues is the battle between short term pay offs and long term prosperity that makes all of the difference.

Every diver we talked with and many dive shop staff and owners we spoke with were as surprised, as we were, to learn

that dive shops do not make money on fills. Filling tanks is in the business category of a “loss leader.” A loss leader is a product or service that is sold at or below cost in order to stimulate other profitable sales. In other words, air fills get you in door of the shop in hopes you will buy equipment or classes that are profitable.

Why is there no money in it? Just a simple viewing of the the numbers for an example air fill tells the tale. Lets say you pay $6 for an air fill. On the front end,  the $8-$12 hour staff has to spend maybe 10-15 minutes or $2 to $3 dollars of that in time to setup, fill your tank and check you out. The shop had to pay thousands for the compressor and air purification system. Compressors are great electricity hogs which add more money to the deficit side of the equation. But the real costs, even after the compressor is paid for is the rigorous maintenance that is required and the associated expendables (e.g. oil and filter material). The replacement costs for  mid size filter materials is about $100 dollars. The staff time for each routine maintenance session is around 2 hours. Average time between a full filter replacement sessions is surprisingly short, often less than 100 hours. For DiveTech on Grand Cayman, during peak season, filter replacement is every 4 days. For Hoodsport ‘N Dive in Hoodsport Washington it is every 2 weeks and they run double the required filters on both compressors. It costs so much time and money to maintain fill system many shops don’t even want to think about it and sadly some don’t.

But to stay in business local dive shops have to offer air fills. During air fill waits is often the time when you sell products to customers. If shops don’t provide air someone else will get those customers (see our nitrox article). If they even slip up once, do not keep up the maintenance program or buy inferior expendables they run risk of having a bad incident. This can turn customers away for good. However, if a dive shop that was doing well falls a little short, the may decide to try to cut corners on compressor maintenance. It can be a slippery slope. You, the diver, can catch it if you know what to look for.


  • Is the shop and compressor neat and clean?
  • Is the compressor room too hot?
  • Does the compressor have an hour meter?
  • Do they have a maintenance log?
  • Is the air intake wide and clear of polluted areas?
  • How does the air taste and smell?
  • Do they have a recent air test result certificate posted?
  • Are their cascade storage tanks hydro-tested and visual inspected the same as your scuba cylinders?
  • How was you visual inspection after getting fills from this shop?

Ask to see the shop’s compressor. If they will not show it too you or give you some flimsy excuse about safety, leave right away. A good shop will be happy to show you their well cared for compressor. When you see the compressor room it should be neat, clean, dry and protected from the elements and tampering. There should be no dust or dirt on around the compressor. There should be no oil leaks or oil on the system. The room should be large enough and well ventilated to keep the temperature a cool as possible. Air conditioning is a plus. The effective life of the filter material plummets as the temperature and humidity rise. The compressor also must have an hour meter.

Look for the air intake. Is it clear of any area that may be polluted by engine exhaust or chemical fumes. Too many shops put their compressors in a shed in the parking lot where a car or truck may sit idling next to the air intake. If the air intake is piped from another area, make sure the pipe is large. The pipe must be .25 inches larger than the compressor intake for every 10 foot of length and every bend in the pipe. If it is PVC pipe it should not be glued at the joints. It is not likely you would check some of these details, but we added them just in case.

Ask to see the maintenance log. If they do not have one, it is likely they are guessing about the timing of maintenance and you should have doubts about the air quality.

Look for or ask to see certificates which may be posted or on file certifying the latest quality of air test.

Take a few breaths from a recent fill from the compressor and smell and taste the air. If you taste or smell anything do not get a fill. However, remember that you will not taste carbon monoxide if it is the system.

Lastly keep your own log of where you get fills or add it to your dive log. This is very helpful if you visual inspector spots excessive moisture, rust, corrosion, particulate matter, or oil (as we had) in your tank. With your own log, you can narrow down shops that gave you the bad fills.


If you want to know more than you ever imagined about air compressors, Jess Stark of Stark Industries has a book for that. He has written and is constantly improving on his book “Compressors for Dummies.” It comes with compressors you buy from Stark or can be purchased separately (although it is pricey). It is part manual and part general education about compressors.

We also recommend Vance Harlow’s "Oxygen Hackers Companion" from Airspeed press.


Do not count on government or other agencies to monitor and keep your air safe. Training agencies, like PADI and NAUI do require their affiliate shops have the air tested quarterly. However, we found many shops that only test once a year and some not at all. Other than that any governing agency requirements that would affect the quality of your air would be much more likely to the brought up in a law suit after the fact. It is very unlikely that an inspector is
showing up a your dive shop to make sure they are following good practices. Good shop owner ethics and customer pressure are the only forces that are going to encourage the dive shop to maintain rigorous testing and maintenance.

We want to the thank Bill Dickson of Bauer Compressors, Jess Stark of Stark Industries and Dane Allen of Seattle Underwater Sports, Ron Ault of  Hood Sport n’ Dive, Greg Beyette of Dive Tech (Grand Cayman) and Divers Alert Network, for help with background information and knowledge for this article.

Safe Breathing!