Abstract of SD-87

National Institute of Occupational Safety and Health, Japan

DSC Data for Reactive Chemical Substances

Shigeru MORISAKI and Takayuki ANDO

:In recent years, the hazard evaluation of chemical substances has become important in chemical industries because chemical accidents such as explosion or fire have occasionally occurred in batch process industries in Japan. These accidents are mostly attributable to thermal hazards such as runaway reaction or thermal decomposition of unstable chemicals in the processes of reaction, distillation or drying.
    The chemical industries in Japan have a tendency to produce more keenly fine-chemicals including Pharmaceuticals and functional resins. The production of these chemicals is usually carried out by a varied and small quantity type process to enhance the value of the chemicals in which many kinds of chemicals may be used without a full investigation of chemical hazard characteristics. Therefore, the potential hazards of chemicals including raw materials, interme diates, and finished goods may be increased in connection with the increase of unreliability for the installations and operations.
    In this report, about 500 chemicals in which functional groups such as nitro or azo group are contained in the molecules were allowed to decompose mostly in inert gas atmospheres using differential scanning calorimetry (DSC : Du Pont 910 pressure DSC). Samples weighing about 1-3 mg were sealed in an aluminum cell with a pin hole on the lid, and in most cases the environment were pressurized with inert gas up to around 34 kg/cm2. Heat rate was 10 °C/min.
    The data obtained are exothermic onset-temperature, decomposition heat, maximum exothermic accelaration and so on. However, about half of the samples listed in this report did not show any exotherms. As is well known, the exothermic onset-temperature are influenced by heat rate which gives lower decomposition temperature with lower heat rate. Moreover, the adiabatic effect which decrease the decomposition temperature must also be considered when a great amount of chemicals is treated. On the other hand, the decomposition heat by DSC is also affected by sample weight or sample phase. Especially, liquid sample tends to evaporate during heating in spite of use of pin hole cell and pressurizing the atmosphere, and consequently the decomposition heats measured from DSC curves have a tendency to show lower values. Therefore, these factors must be taken into consideration when one apply these data to the actual state.

Diagram Related to Flashing Temperatures and Flammability Limits (2)


: For assessing the explosion-hazard of a gaseous mixture in equilibrium with a flammable liquid, such as the atmosphere above the liquid surface in an enclosed vessel, it is of little use to show the concentration for the flammability of the vapor in air, but temperatures that are defined as lower and upper flashing temperature, are essential. There have only been a few instances so far where a series of these measured or estimated temperatures were reported for a variety of flammable liquids.
    The author has been aware of the importance of the above two flashing temperatures for some time past and examined by measuring them for many substances. Some of the results are given in this report, in the form of temperature vs. vapor pressure diagram which shows the relationship between flashing temperatures and flammability limits, for estimating the explosion-hazard characteristics of industrial chemicals or liquids at a glance.
    In the report the general idea and the importance of the flashing temperatures are first described, subsequently followed by the method of measurement and main points of drawing the diagrams. Secondly, the diagrams for important substances from industrial safety point of view are presented for each substance.

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