Look at this photograph and consider the challenges of fighting a fire in the bitter cold. 

• It’s bitter cold and you need to put people into it for hours while you battle a fire
• Those people are getting covered in water
• the water you’re spewing onto the structure is freezing as soon as it leaves the tip of the hose
• you’re icing over the trucks, the ladders, pretty much every tool you’re using
• The truck that you’re spewing water from is now sitting in freezing water
• you’ve added thousands and thousands of pounds of weight to a weakening structure

I’m sure there are more, but this is what immediately comes to mind. I do not envy the men and women of the Fire Department - but I’m glad they’re there.