interesting, everytime I've seen them flowing its been clear,maybe the bad water is gone by then. Hum. My thought though was more standpipes as that takes a mear turning of a wheel in the stairwell.Those pipes are much larger and are verticle so any junk i would figure would not be lying in the pipe.

I'll say everytime I've opened up a line running off a standpipe its looked good to me. We connect one floor below the fire,stretch the line up the stairs,crack the line to bleed it off then attack the fire. In fact a month a go we practiced using a 2 1/2 off a standdpipe . all the water was clear. Oh this was done on the roof( they get amd when you destroy the office) and more of advancing a 2 1/2 up the stairs and out on to the 'floor" ( roof) but we did flow water and it was clear .

Perhaps these places where its black and full of gunk should do a little PM and water tests and flows . I'd have real concerns about hoseline pressures and even if it'll flow at all.

Ya I was not clear about heat/smoke sprinklers . I meant two things.The smallest fire will make a lot of smoke,and two if you some how set them off( to big a fire) you'll be wet as well.

But then when the FD shows up we could give you some water I guess.....