worked on a main steam header on the last outage, preheat at 450 constant. All of the welders wanted to die. Heat exaustion and stroke are very likely at extended exposure. That being said, I had to do some intenal crack repairs on the ends of the existing header to make it to the next outage to be replaced at arms lenght inside with TIG gloves and stick gloves over them blistered my knuckles within 4 rods. After that we used TIG gloves, stick gloves, a cool pad, and leather sleeves. Very hot and exhausting, so please be very carefull, I will have the scars for the rest of my life. A constant reminder to watch out and think ahead. Keep your welders in the proper PPE, hydrated, and rotate to a cool place or cooler than where they are welding if prolong exposure is needed.