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flash point temperature. As a result, this temperature is also referred to as the lower temperature limit of flammability (LTL). However, in reality, these two temperatures (FP and LTL), may not always be the same. Knowledge of the disparity between these two points will help better assess the flammability hazards of a specific chemical as well as help implement the proper safety precautions during handling.

Table 1: Flash Point and Lower Temperature Limit of Flammability Results

To understand the variation between the lower temperature limit of flammability and flash point, tests were performed to compare the results. The lower temperature limit of flammability tests were conducted using ASTM E1232 “Standard Test Method for Temperature Limit of Flammability of Chemicals” modified to be conducted in a 5.3-L stainless steel spherical vessel using a fuse wire ignition source for safety and environmental purposes. The criterion for a positive ignition was a 7% pressure rise above the starting pressure. The flash point tests were performed using ASTM D3278 “Standard Test Methods for Flash Point of Liquids by Small Scale Closed-Cup Apparatus”. These tests were performed on four different chemicals and the results are summarized in Table 1.

LTL (oC)

Flash Point (oC)

Chemical

Organosulfur Compound Lactam Ring Compound Pyridine Compound 1 Pyridine Compound 2

89.5

81

81.5

79

100

92

119

137

Vessel Size and Geometry – As the size of a vessel increases, the heat losses to the vessel wall become negligible. Through minimizing heat losses to the vessel wall, more heat is transferred to the combustion reaction, promoting flame propagation. This results in a widening of the flammable region and potentially allowing for combustion to occur at lower temperatures. Furthermore, a study performed by Takahashi, Urano, Takuhashi, and Kondo (2003) determined that flammability properties should be determined using either a spherical vessel or a cylindrical vessel with a diameter of at least 30 cm and a height of at least 60 cm to minimize the effect of flame quenching which may artificially result in a narrower flammable region. Ignition Source Location – A lower ignition source elevation in a vessel has been shown to widen the flammable region as compared to a central ignition source location (Van den Schoor, Norman & Verplaetsen, 2006). With a lower placed ignition source, a larger percentage of the combustible mixture participates in the upward moving combustion reaction with minimal heat losses to the wall, thereby, causing more heat being transferred to the combustion reaction resulting in a wider flammable region. The deviation between the values determined by these two tests is a result of differences in the test apparatus and methodology used in each of these experiments. It is important to understand that flammable properties are influenced by numerous factors. Below are a few factors that may provide an explanation for the differences between the two test results: 2. 1.

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