Volume 27, Issue 6 (November 1999)
The Effect of Kinematic Viscosity on the Flash Point of Liquids Determined by ASTM D 93 Procedure A, ASTM D 93 Procedure B, and ASTM D 56
The flash point of a liquid material is used to classify whether the material is flammable or combustible. ASTM D 93 is used to determine the flash point of various liquids either by Procedure A or Procedure B. There have been reports of flash point depression when viscous materials were tested using ASTM D 93 Procedure A relative to ASTM D 93 Procedure B. A multi-sample interlaboratory study was conducted to determine the effect of the kinematic viscosity of a liquid material on the observed flash point when tested according to ASTM D 93 Procedure A relative to the results when tested according to ASTM D 93 Procedure B. The results of the study indicate that liquid materials with kinematic viscosities greater than 13 mm2/s at 40°C gave lower observed flash points when the flash point was tested using ASTM D 93 Procedure A compared to the flash point tested by ASTM D 93 Procedure B. A possible explanation is a lag in the temperature detected by the temperature-measuring device as the kinematic viscosity of the liquid increases, especially when equilibration of the temperature of the vapor and the bulk of the specimen is not established before the flash point is detected. This temperature lag effect is more pronounced when using D 93 Procedure A than when using D 93 Procedure B. A similar study was conducted with ASTM D 56, another flash point test method. The effect of kinematic viscosity on the observed flash point by D 56 is less apparent than that observed when using D 93 Procedure A.