ehuber:
Hydros are done once every 5 years. VIPs are done once a year. VIPs are done to ensure that the inside of the tank hasn't taken on any water and started to corrode. If you bring an empty tank in for me to fill, I will be concerned about why it's empty. Sure you can tell me your just bought them and they haven't been used yet. But how do I know this is true? How do I know you aren't just saying that? How do I know you didn't drain the tanks on your last dive and let water in which has now corroded the steel and made the tank unsafe to fill?
Let's say the tanks and valves were oxygen cleaned. Since the cleaning, you brought them to a shop that doesn't have oxygen clean air and got them filled several times. Now you take them back to a shop that does PPB to get nitrox. The tank monkey connects the oxygen to the valve, cranks it open and BOOM, the adiabiatic heating and high oxygen content causes the hydrocarbons to ignite. The proper thing for the shop that was pumping air into your tanks would have been to remove the oxygen service label and replace it with a label that states the tanks are not oxygen serviced.
Unfortunately there are a lot of shops out there that don't follow strict standards. There are a lot of shops that don't even know the standards for doing PPB fills. I'm not saying it's right for the shop to be bending you over, but they do need to look out for their own safety.
