Is it okay to use plasma to cut aluminum on a water table?
When cutting aluminum with plasma over a water table, small particles of aluminum and aluminum oxide form. These particles cool as they hit the water and sink to the bottom of the table. Once at the bottom, the aluminum oxide absorbs the oxygen leaving only hydrogen behind, since water is composed of hydrogen and oxygen. This hydrogen rises to the surface of the water in the form of bubbles, which then pop and dissipate into the surrounding air in very small quantities.
This production of hydrogen is most likely harmless, but there are some water table designs that utilize a submerged tank or chamber. This tank or chamber is used to raise and lower the water table rapidly by displacing water with low pressure compressed air. If this type of water table is in use, it is possible for some of the aluminum oxide particles to get stuck inside the lower chamber. Once inside the chamber, the aluminum oxide will absorb the oxygen leaving just the hydrogen. Over time and much use, a relatively large bubble of hydrogen could form, and this could potentially cause an explosion in the presence of an ignition source.
Consult with the table manufacturer and other experts prior to cutting aluminum to implement a risk assessment and mitigation plan that eliminates the risk of detonation by preventing hydrogen accumulation.
Also, make sure that the water table, fume extraction (ventilation), and other parts of the cutting system have been designed with aluminum cutting in mind.
Do not cut aluminum alloys underwater or on a water table unless you can prevent the accumulation of hydrogen gas.
Note: With proper mitigation, most aluminum alloys can be plasma cut on a water table. An exception is aluminum-lithium alloys. Never cut aluminum-lithium allows in the presence of water.