Welding sparks can be hot enough to melt into plastic they land on, but I have yet to see one melt through. The exterior lens protectors on welding hoods are .03" thick polycarbonate, and my welding hood gets much closer to the action then my player.
Grinding shrapnel can be both hot and dirty. Some grinding/cutting results in melted metal shrapnel flying in any direction. We use plastic weld curtains in the shop to keep from spraying our neighbors. The fiberglass and zirconium oxide used in the grinder consumables is very dirty and tends to stick to whatever it lands on.
Metallic dust is created when the 10,000 degree F arc from the welder turns metal to liquid, some metal is vaporized along with any oils or oxidization and this gets into everything. We have lost more than one computer motherboard to this dust. Also nearly everything plastic builds up a static charge that grabs this dust. Somehow the dust tends to etch into the plastic and is very difficult to remove.
I purchased a $2 plano tackle box and had some very low density foam from an old RC car to make my case.
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