i dunno about specific photo labs but the offices here are above 17 and usually 23 is the max that people can comfortably work.
If you were approching your employer suggest that it is not a safe place of work because at these temps fainting, dizziness, heat rash, headaches are very likely to occur. He will most likely a) send you home b) rotate your working (ie 2 hours printing 2 hours checking & packing 2 hours counter service) c) buy you fan's for localised cooling - a bit futile because the machines give out a load of heat. Suggest the latter 2 and see what he says.