yojimbo,
in '93, we did a water line for the city of Sheridan, Wy. Our smallest line was a 12" sch 10. Yes I reread that, NO TYPO! We hand mitered and custom built all the 30°, 45's, 90's etc. It was also cement lined!. Our helper was 5'-0" and weighed less than 90#s. We tied a rope to his feet and he could crawl up a 12" cement lined pipe (had to repeat that!) and patch the internal grout after welding. One man would pull on the rope and another would be at the other end so he could give commands to the "rope man" to halt the pulling when he got into a bind. This was not a rapid process on entry or egress.
On a similar note, back in 75 when I weighed 140, I spent 30 days of my "apprenticeship" with ARMCO Steel crawling inside 18" sch. 40 pipes fixing busted X-rays. I was not amused since my buddy who only weighed in at 130 missed out on this. Being a union shop though, he had 1 week's seniority on me and was able to pass it off on the FNG. And FWIW, I had no helper or hole watch. Just me with a hand full of tracing paper skins, an air hose, die grinder, drop light, and welding lead in the Houston August sun and a 100 yards of ugly pipe welds. Whaaaaahhh, whimper!
What we'll do for a buck... and no OSHA.