Customer Uses
Training & Education


Previous | Back to Newsletter | Next


Q. Can wet cutting of aluminum cause combustible dust? What measures would you use? Also, do you know anything about cutting polyethylene/polypropylene on a CNC machine? Will this cause combustible dust and what measures would you use?

A. When you cut aluminum over a water bed (often called a water table) the small, resolidified particles of aluminum and aluminum oxide cool and sink to the bottom. Aluminum has a tendency to absorb oxygen from water, leaving just the hydrogen.

If you look closely at the water in a water table after cutting aluminum, you will see small bubbles rising and popping at the surface. These are hydrogen bubbles which under most conditions just dissipate into the surrounding air in very low volumes.

If the water table has areas that can trap these hydrogen bubbles (hydrogen is lighter than air so it will rise,) these bubbles can accumulate and cause an occasional explosion when the plasma arc or a spark causes ignition. Hydrogen could also become trapped under a fresh sheet of material if the material was left on the table and was somehow bowed upwards, providing a place for hydrogen to accumulate.

Though many hundreds of installations cut aluminum on a water table, it is best practice to ensure the manufacturer of the table has designed the table with aluminum cutting in mind. It is also a good idea to lower the water level, then raise it if a plate or sheet has been left in place. This will remove any hydrogen that may get trapped.

By cutting polyethylene/polypropylene, I am assuming that you mean metal sheets that have a protective masking made of this material. Cutting non conductive materials such as these is not possible with plasma. If it is masking material, the plasma will cut through to the metal. Accidental combustion should not be an issue, however there could be some dangerous fumes released from the plastic material. For that reason you should check with the material supplier.

Best Regards, Jim Colt

Hypertherm's Jim Colt is an avid fabricator who has worked with plasma cutting systems for more than 30 years. He is the author of many articles and white papers on plasma cutting and a frequent speaker at key industry conferences. If you have a question you'd like Jim to answer please send it to

Get answers to more of your metal cutting questions at the Hypertherm Cutting Institute.
Cut With ConfidenceT

Hypertherm Inc. Etna Road, P.O. Box 5010 Hanover, NH 03755 USA