It has been estimated that, were all the air in your pneumatic rifle's fully-charged air tank to BE released instantaneously, the explosive blast would be as lethal as a half stick of dynamite! 
This is the powerhouse of your rifle and is what drives pellet after pellet at high velocity downrange with such stunning accuracy.

Your air rifle is, effectively, a small, efficient bomb and must be treated with due care and respect, especially when working on it. The air tank or reservoir of your rifle can be detonated by impact, heat, drills and even rapid decompression. The integrity of the tank's walls are of huge importance in containing air under very high pressure. Any scarring, denting or other deformation to the air tank MUST render the rifle unfit for use until either checked by an expert or the tank is replaced. This is NOT negotiable! If it explodes while you are holding it in a firing position you will suffer potentially lethal injuries!

Before you commence work on your air rifle you should stop to consider if the work you intend to carry out will involve the air system in any way. If the air tank is removable, take it off the weapon until work is complete, otherwise slowly drain the air tank before commencing any repairs. This will not only render the weapon inherently safe but will also remove the risk of injecting high pressure air through the skin. THIS CAN PROVE FATAL!

This Author has; 
1. Witnessed an amateur gunsmith shoot himself in the face with valve components by unthinkingly pulling the trigger on a semi-stripped but fully-charged and cocked Falcon Raptor-
2. Seen a contact lens blown off an eyeball by an accidental discharge of air while peering into a semi-stripped but fully-charged B4-
3. Examined a neat 1.5" hole blown in the 3/4" plywood end wall of a garden shed by a Webley Axsor's reservoir end cap that had had two of its retaining screws removed - the owner had forgotten to drain the air tank with the result that the end cap became a high velocity aluminium projectile. (It was never found and the reservoir was wrecked by the tearing out of the third, remaining half-undone screw.) 

Use the correct tools for the job, avoid damage to the rifle's components at all costs and keep everything clinically clean.

ORDINARY OIL IN A HIGH PRESSURE AIR SYSTEM WILL SPONTANEOUSLY IGNITE - WITH POTENTIALLY DEVASTATING RESULTS!   USE ONLY DIVER'S SILICON GREASE FOR LUBRICATING ANY PARTS THAT COME INTO DIRECT CONTACT WITH THE AIR SUPPLY.

You don't take risks when your rifle is loaded - so use the same caution in your workshop and be safe!

IF IN DOUBT - DON'T!

Now, Happy Tinkering!
Regards
Bob Craske