Hazard control gases

The two different, but related, considerations in waste disposal are hazard control and loss prevention in the treatment and disposal operations, and the control of environmental hazards. With gas and liquid streams the control of on-site hazards arising from the chemical properties and processing operations generally follows the principles summarized in earlier chapters. The measures necessary with solid wastes may, however, differ, particularly if they are heterogeneous in nature and disposed of on land. 

Mine gas is one of the important hidden trouble to influence coal mine safety production (Shi et al., 2006), the abnormal gas emission will usually lead to coal mine gas accident. Gas emission is affected by many factors (Zhu et al., 2007 Guo et al., 2009 He et al., 2008), the judgment of abnormal gas emission is not only important to the real-time monitor of the gas concentration (Zhang et al., 2012), but also important to the discrimination of the reason of abnormal gas emission. Therefore, the dynamic evaluation of gas emission hazard danger level combined with gas monitoring data plays an important role on gas prevention and gas disaster control when it does dynamic early-warning of coal face gas emission (Lv et al., 2006 Gong et al., 2012). 

Once established, the methanogenic bacteria will help to control the pH at or near neutrality such that acetogenic phases (pH S - 6) and methanogenic phases (pH 6 - 8) of landfill can be cleariy discerned. At this stage, landfill gas production will increase as a result of the bacterial activity, with the result that carbon compounds that might otherwise contribute to leadiate TOC may be converted to landfill gas with a resultant decrease in this parameter within the MSW leachate (Table 6). The leachate hazard will therefore be reduced with a consequent increase in the landfill gas hazard. 

Control of gas-phase migration represents another important objective of engineered covers. In the case of municipal solid waste, failure to adequately control and vent the methane gas (CH4) generated by decomposition of the waste represents a potential explosion hazard. Thus, the final cover serves both to prevent the escape of large quantities of methane gas and to assist in the collection of the gas for controlled venting through an engineered collection network. 

The restricting orifice and the liquid knockout pot both guard against entrainment of liquid chlorine, which might create a serious hazard in the process. The orifice, sometimes replaced by a flow control valve, limits the flow to no more than the vaporizing capacity and so helps to avoid entrainment. Other possible measures include a high-level shutdown on the vaporizer and gas temperature control or low-temperature shutdown. The knockout pot is the second line of defense. 

Holmes MJ, Redinger KE, Evans AP, Nolan PS. Control of mercuiy in conventional flue gas emissions control systems, in Fourth international conference on managing hazardous air pollutants, Washington, DC, November 12-14, 1997. 

Prevention is the first priority in the mitigation of gas hazards. The first step is to control access to vulnerable areas. A card-access system was... 

The two main methods of explosion hazard control are explosion prevention (e.g. preventing formation of explosible dust clouds, removing all possible ignition sources, creating an atmosphere that cannot support combustion) and explosion protection (e.g. venting, suppression, containment and/or isolation). Quite often it is difficult to guarantee explosion prevention (e.g. due to equipment/instrumentation failure and/or human error). Explosion protection usually is pursued to protect personnel and minimise plant damage. Despite the similarities with gas explosions, dust explosions can be quite different ... 

With these waste-minimization techniques, methanol synthesis is relatively clean, and poses no unique environmental hazards. The need for environmental controls is more closely associated with the synthesis gas generation process. 

High-efficiency air filters are sometimes used for emission control when particulate contaminants are low in concentration but present special hazards cleaning of ventilation air and other gas streams exhausted from nuclear ant operations is an example. 

While some video display screens such as liquid crystal, gas plasma or vacuum fluorescent displays do not present the same charged screen hazards as CRTs, this does not imply that they are safe for use in hazardous locations. This requires special design and certification for use with a given flammable atmosphere. Non-certified equipment used in locations classified as hazardous under Article 500 of NFPA 70 National Electrical Code require a purged or pressurized enclosure to control ignition hazards as described in NFPA 496 Standard for Purged and Pressurized Enclosures for Electrical Equipment. The screen in this case is located behind a window in the enclosure. 

Pistons may be of segmented construction to permit the use of one-piece wear bands. One-piece wear bands are a requirement in API 618. Pistons have a problem in common with humans—a weight problem. Weight in a piston contributes directly to the compressor shaking forces and must be controlled. For this reason, aluminum pistons are often found in larger low pressure cylinders. Hollow pistons are used but can pose a hazard to maintenance personnel if not properly vented. If trapped, the gas will be released in an unpredictable and dangerous manner when the piston is dismantled. 

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