Define flash point and fire point? Give its significance.
Flash point:- Flash point is defined as the lowest temperature at which the lubricant gives off enough vapours to cause a momentary flash when a standard test flame is brought near it.
Fire point:- Fire point is the lowest temperature at which the oil vapours catch fires for at least 5 seconds, on being lighted by a test flame.
Fire point is usually 5-40° C above the flash point. A good lubricant should have flash point at least above the working temperature. This ensures safety against the risk hazards. Thus flash point acts as a guide for the safe storage, transportation and use in machine. Good lubricant oil should have high flash and fire point.