almost everytime It was the result of a poorly (Or no training ) Engineer that had way to much pressure on the hose line.
when you see three Firemen get lifted off their feet its kind of a sign of to much pressure!---LOL
I was a Water Supply officer with the FD in my later 4-5 years after we got Large Diameter Hose and hydraulics was just kind of my thing well before then, I swear some of the Engineers there were just pitiful and many had been Engineers for many years as well.
course IF you can't multiply or divide then likely you can't work out formulas>
what can I say hiring requirements kind of went down the tube about 1980.