Big rig fires used to be rare .Diesel fuel can be hard to ignite, especially if its cold. But things may be changing today. Modern electronic engines-especially the new emissions regulated engines -tend to run hotter fuel back to your tanks. Diesels return most of the fuel they draw from the tank back to the tank unless your at wide open throttle. Use to be that the return fuel was cooler -under 140 degrees- but the newer engines are pumping 200 degree plus fuel through the return line back into your tank. Fuel at this temperature is much easier to ignite creating a much bigger fire hazard in any accident that traps you in your rig. The "flash point" (" the lowest temperature at which a petroleum product will burn. Below this temperature insufficient petroleum vapour is available to support combustion.") for diesel is suppose to be 144 degrees F. Fuel temperatures above this are hazardous.
This picture shows two of your major problems -big exposed tanks and a battery box close by. Here's a common scenario: You hit something up front and break the axle loose, the axle swings back taking out the battery box which in turn punches a whole in the tank. The shorted out batteries explode, igniting the fuel spray from the tank. We once worked on a case where a rig hit a horse on the interstate and generated this kind of accident. Once the steering axle breaks loose you've lost control and your going over unless you can stop first which is unlikely unless your moving really slow. Get the battery box away from the tank if you can. Also: Bigger tanks are bigger targets, how much capacity do you really need?
Here's another problem - exposed lines. Unless these are all water lines, something in them can burn, especially if its hot diesel oil. Make sure all your fluid lines are inside the frame rails, in the recess if possible. Make sure your crossover line isn't hanging down, they should be protected by the frame cross members. Make sure they don't leak!
School busses have tank guards like these:
(Crude but effective)