Please understand I am not trying to cotradict here, IF you are going to use the polyester resin with MEKP (Methyl Ethyl Ketone Peroxide) Please use the proper PPE (Personal Protective Equipment) Chemical resistant gloves, goggles, tyvek coveralls (impermeable) And most of important of all,.... FOLLOW THE MIXING DIRECTIONS!!!
I have been doing Advance Composite Repair for more the 16 years now in the US. Navy, in fact the US NAVY has banned the use of MEKP completely due to its rather nasty habit of destroying internal organs.
Dont mix it hot, you will make your resin brittle, and you will also risk a possible exothermic reaction. (simply put) a chemical fire you cannot put out.
There are so many other types of resin to use that are easier to mix, like 1 to 1 ratio resins that dont use MEKP. I would highly reccomend using those instead!
It is safe to use provided you strictly adhere to what the can say to do.
I hope this helps!