Quote:
Originally Posted by gorrilla
take a soda bottle down about 100 feet under water and fill it with air and let it float the the surface
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This hypothesis does not make PVC safe to use with gases under pressure.
If you do that, you will have to fill the water bottle to a high enough pressure to match (or exceed) the water around it, otherwise it will be crushed by the water pressure. If you make the air pressure in the bottle match the ambient water pressure around it, then at 100 feet down everything will be in equilibrium and nothing spectacular will happen.
Despite being at the same pressure, the mass of air inside the bottle is less than equivalent mass of water at the same volume, so the bottle will float upward. As it hits the surface, the relative pressure difference between the bottle and the water around it will begin to skyrocket. At it hits the surface, the pressure of the water bottle will be very high compared to the water/air around it, and then has a high chance of violently exploding. The resulting possible explosion would be very much like that if you filled a water bottle 1/3 with water, put in some dry ice, screw on the lid, then run like there's no tomorrow - e.g. a
very violent and VERY LOUD explosive decompression.
The same thing can happen to the dissolved gases in the blood stream of divers who surface too fast, resulting in
the bends.
Quote:
Originally Posted by gorrilla
by the by water is just as dangerous as air under pressure and water under pressure explodes things too
they test scuba tanks by filling them with water to 3000psi
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I never said water [or more generally, liquids] under pressure are not dangerous, as in fact it can cut through objects six or more inches thick in the form of a waterjet.
How materials react to these differences between pressurized liquids and gas
is what I am concerned about. PVC reacts much more violently during a fracture with pressurized gases rather than pressurized liquids,
which is why PVC is banned by OSHA for any pressurized gas applications.
Avoiding PVC for pressurized gases is like never pointing a gun towards anyone at any time, or always using your seatbelt in a car. Sure, you can always claim a few times where one has ignored these concerns and nothing bad happened. But accidents are just that - accidents - and by not following safety guidelines you seriously increase the risk of serious bodily harm to both yourself and anyone around you.