why fire engine is red in colour?  

to indicate danger! is not fire red in colour?

to identify clearly from longer distance

Red colors frequency is like that it is visible from a long distance and as fire engine is on the road most of the times it means an emergency,so its color is red so that people may give its a way sothat it reaches where ever it is going quickly and save people there.

You must be knowing the Colour Band.
So the Intensity of red colour is most among all.

Hex triplet #FF0000
RGB (r, g, b) (255, 0, 0)

Also,
Red catches people's attention, and is often used to indicate danger or emergency.

* Red symbolizes heat and fire. Taps for hot water are often labeled red. Red is commonly the color of fire alarm boxes, fire extinguishers, and the firefighter profession itself.
* Red denotes "stop" in, for instance, stop signs, traffic signals, brake lights, or the flashing lights of a school bus.
* Red is the color of blood, and a Red Cross, Red Crescent or Red Crystal emblem signifies medical personnel, facilities, or equipment, or the Geneva Conventions.
* Red indicates extreme danger on Western color-coded scales, such as wildfire hazard signs or the U.S. Homeland Security Advisory System. It also denotes the maximum level of danger and preparedness as in the phrases condition red and red alert.
* In auto racing, a red flag signals all cars to immediately stop.
* The red line is the maximum speed an engine and its components can safely run.

I hope this much have solved your query! ;)

related resources: emergency preparedness, medical alert, medical equipment

its danger symbol colour

Because red is simple to be reached by eyes.

i dont know

i dont know

because red is a sign of danger and it is visible from far also... so its red in colour