Autoignition temperatures apparatus

The niaxiinwn spontaneous ignition temperature (SIT) or autoignition temperature (AIT) is defined as die minimum temperature at wliicli combustion occurs in a bulk gas mixture when die temperature of a flaiiunable gas-air mixture is raised in a unifonidy heated apparatus. The autoignidon temperature represents... 

Measurement of autoignition temperature can vary based on the size of the vessel (i.e., the test apparatus) holding the vapor and the strength of the ignition source. Because of these factors, there is often some variability in quoted autoignition temperatures. The convention is to use the lowest value found in literature. 

The autoignition temperature (AIT) or tlte maximum spontaneous ignition temperature is defined as the maximum temperature at which combustion occurs in a combustible bulk gas mixture when tlie temperature of a flammable gas-air mixture is raised in a uniformly heated apparatus. The AIT represents a tlircshold below which chemicals and combustibles can be handled s ely. (The AlTs of selected substances arc available in the literature. ) The AIT is strongly independent on tlie nature of hot surfaces. The AIT may be reduced by as mudi as 100-200°C when the surfaces arc contaminated by dust. When tlie temperature of a flanuiiable mi.xturc is raised to or above the autoignition temperature, ignition is not spontaneous. Most notably in liquids, there is a finite delay before ignition lakes place, i.e., a lapse between the time tlicrc is a flammable mixture reaches its flame temperature and tlie first appearance of a flame. An equation tliat correlates with the ignition temperature is also available in the literature. ... 

The relevant flammability data is obtained in a specially designed 20 litre sphere. The main features of this explosion vessel include Hastelloy C 276 walls, central ignition with spark, hot wire or pyrotechnic ignition source, 200 bar pressure resistance, ambient to 300°C initial temperature, easily opened for frequent cleaning. This apparatus allows precise determination of the flammability limits, autoignition temperature, explosion overpressure, rate of pressure rise and flame speed. A review of flammability data in chlorine is given. 

A special feature of the autoignition of many organic solvent vapours, including those from hydrocarbons, alcohols, ethers, aldehydes and acids is their ability to form cool flames at temperatures well below their autoignition temperature as measured in the standard apparatus [10]. A cool flame is a form of incomplete combustion, usually involving the formation of an unstable peroxide and its decomposition to an aldehyde. Cool flames emit a pale blue light which is visible only in the dark and on their own produce a relatively modest ca. 20-50 K) temperature rise, hence their name. The main hazard with cool flames lies in their potential for transition into true combustion, and that their products are often less stable and more reactive than the original compound. 

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