Ethylene oxide flammability limits

Both LFL and UFL valnes for mixtnres can be estimated by nse of the Le Chatelier eqnation (Growl and Lonvar 1990). However, the methods have some limitations with respect to calcnlating the UFL for certain mixtnres. Britton (1996) determined that the eqnation does not apply to the UFL of mixtnres containing decomposable components snch as ethylene oxide or to mixtnres containing ethyl ether. Mashnga and Growl (2000) discnss the derivation of Le Chatelier s mixing rnle for flammable limits. 

Vanta et al (Ref 2) determined the detonation limits of propylene oxide/air mixts to be 2.7 to 14.4 volume %, or much narrower than the flammability limits of ethylene oxide/air (see Table 3). They also measured the lower detonation limit for n-propyl nitrate/air and found it to be 2.2 volume %... 

Ethylene oxide is a colorless gas with an aromatic odor. The threshold limit for the odor is 700 ppm. The OSHA specification for worker exposure is 10 ppm. The toxicity of ethylene oxide is similar to that of ammonia. It causes conjunctival and respiratory irritation, dizziness, headaches, and vomiting. It is known to be mutagenic and may be carcinogenic. By-products include ethylene glycol (bp, 198.9°C) and ethylene chlorhydrin (bp, 128.4°C). Pure ethylene oxide is flammable and explosive. It is generally mixed... 

The ethylene oxidation rate is proportionhUo the oxygen concentration. This means that the air-to-ethylene ratio has a predominant influence on the conversion and yield. For practical purposes, however, the optimal ethylene concentration is determined by the flammability limits of the mixtures with oxygen or air, and by the olefin loss in tbe off-gases. 

Hence, in ambient conditions, the air/ethylene mixture exhibits an auto-ignition range between 2 and 28.6 per cent volume ethylene. Thp lower limit is substantially the same with rising temperature, while the upper limit is increased. For mixtures of air and ethylene oxide, the lower limit is 2.5 to 3 per cent volume oxide, and the upper limit approaches 100 per cent. To remain below 3 per cent volume in both cases, it is necessary to use inert diluents. The presence of carbon dioxide, which may also result from the recycling of the products of combustion reactions, can help to reduce the flammability... 

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