The pair were unaware that they needed a hot-work permit.    From Wordnik.com.  [AroundTheCapitol.com] Reference

The ability to produce components in a range of materials including hot-work steels, stainless steel, cobalt chromes and Inconel, plus titanium and aluminium alloys, presents the aerospace industry with large potential for direct part production using ALM.    From Wordnik.com.  [Manufacturingtalk - manufacturing industry news] Reference