LA Police Gear has 5.11 fire-resistant T-shirts on sale for $5 each, down from $40. Quite a deal. The fit is generous; I have a 46"-47" chest and I found the XL a bit loose, but the L fit very nicely. The seams are all flat sewn and the armpits have a gusseted panel for an unrestricted fit.

A fire-resistant T-shirt doesn't make you fireproof but its one less thing to burn & melt into your skin.