Flash Point and Autoignition Temperatures of Common Vehicle Fluids

Laboratory Measurements

 

Laboratory flashpoint measurements provide useful information regarding the temperature at which a fluid may release enough vapor to sustain a flame in ideal conditions. Autoignition temperature measurements require more interpretation. In the laboratory, autoignition is measured by placing samples inside nearly closed chambers, without airflow, and with the benefit of instrumentation to identify even fragile and fleeting ignition events. The values shown in the following table tell us the lowest possible ignition temperatures for the fluids listed when under ideal circumstances.

The values in the table are presented for general reference and as such do not need to be memorized. The tabulated values provide a way to compare the relative flammability of various fluids and can be used as a resource for practical fire investigations.

 

Fluids Flashpoint [12] oF Autoignition Temperature [13] oF
Automatic Trans. Fluid [ 2, 4] 302-383 410-417
Brake Fluid [ 2, 4, 10, 11] 210-375 540-675
Compressor Oil ( PAG and ester) [ 4, 8] 392-500 410-714
Coolant    
    Ethylene Glycol (100%) [ 1, 2, 4] 232-260 725-775
    Ethylene Glycol (90%) [ 2] 270 N/A
    Propylene Glycol (100%) [ 1, 4] 210-230 700
Diesel Fuel [ 1, 2, 3, 4] 100-204 350-625
Ethanol (in gasohol) [ 1, 3, 5] 55 685
Gasoline (50-100 octane) [ 1, 2] -36 to -45 536-853
Gasoline (unleaded) [ 4] -45 495-833
Engine Oil (conventional and synthetic) [ 1, 2, 4] 300-495 500-700
Methanol (in windshield fluid) [ 1, 2, 3, 4, 5,14] 52-108 725-878
Power Steering Fluid [ 2, 4] 300-500 500-700
Refrigerants    
    R134a 140 KPa (5.5 Psig) [ 7] 350  
    R134a[ 7,15,16]
Not flammable at ambient temp. and atmospheric pressure
1370-1418
    Freon 12 [17] >1382
    HCFC-22 [ 9] Flammable at 60 psig
    Hydrocarbon Refrigerants Flammable Flammable
Starter Fluid (ethyl ether) [ 5,18] -49 320

 

Note about the table: When various sources had different flashpoint or autoignition temperature values for the same material, the range in the table was increased to include all values found.

To utilize flammability characteristics in investigations, it is necessary to also have measurements made in vehicle environments.

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