Imagine that you are a firefighter, hose in hand, approaching the flames inside a burning building. You open the nozzle on your attack line and...nothing. Someone has driven over the hose outside in the street and ruptured it causing a loss of pressure. Not only are you unable to fight the fire, you are at risk now too.
This imaginary driver is guilty of two traffic offences. The obvious one is driving over an unprotected fire hose without the permission of the fire department official in command. What you may not be aware of is that you are prohibited from driving or parking within 150 meters of fire apparatus that has stopped in answer to a fire alarm. This is also the minimum mandatory following distance that you must maintain from a fire vehicle answering an alarm.
During the initial attack at a fire scene, firefighters are focused on saving life and property. They do not have the time or the manpower to guide drivers over the fire hoses nor to watch out for you as you drive through their scene. The law makes it simple for drivers in these cases, don't go there, period.
These rules are aimed at insuring the safety of emergency crews and require you to either wait until police arrive for traffic direction or to find another way around the scene of the fire or fire alarm.
Reference Link: http://www.drivesmartbc.ca/emergency-vehicles/dont-drive-over-fire-hose