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Annotated Dictionary of Construction Safety and Health
Published in Charles D. Reese, James V. Edison, Annotated Dictionary of Construction Safety and Health, 2018
Charles D. Reese, James V. Edison
Exhaust valves and exhaust pipes are to be provided and operated so that the working chamber is well ventilated, and there are no pockets of dead air. Outlets may be required at intermediate points along the main low-pressure air supply line, to the heading, to eliminate such pockets of dead air. Ventilating air is not to be less than 30 cubic feet per minute. The air in the workplace is to be analyzed by the employer, not less than once each shift, and records of such tests are to be kept on file at the place where the work is in progress. The test results are to be within the threshold limit values for hazardous gases, and within 10 percent of the lower explosive limit of flammable gases. If these limits are not met, immediate action to correct the situation must be taken by the employer. The temperature of all working chambers which are subjected to air pressure shall, by means of after-coolers or other suitable devices, be maintained at a temperature not to exceed 85 degree F.
General Princlpes
Published in Martin B., S.Z., of Industrial Hygiene, 2018
Explosive limits are very similar to flammable limits. The lower explosive limit (LEL) is used to determine when the concentration of material is too small for an explosion to occur. Similarly, the upper explosive limit (UEL) defines the level at which there is too much material present for an explosion to occur. Once again, the industrial hygiene profession is usually more concerned with the LEL. They must determine what concentration below the LEL is acceptable for a given material (refer to Figure 2.1). One factor of importance in this determination that is often ignored is the effect of pressure. Increasing the pressure will raise the flash point, while lowering the pressure will decrease the flash point. Other factors that should also be considered include: oxygen content, chemical composition, turbulence, and confinement.
Basic Chemical Hazards to Human Health and Safety — I
Published in Jack Daugherty, Assessment of Chemical Exposures, 2020
Explosive limits define the range of vapor concentrations in air that constitute an explosive mixture. The upper explosive limit, or UEL, is the highest concentration of the vapor that will explode. Any concentration of vapor above the UEL will not explode and the atmosphere is said to be too rich. The lower explosive limit, or LEL, is the lowest concentration of the vapor in air that will explode. Any concentration of the vapor less than LEL will not explode and is said to be to lean.
Removal of a mixture of formaldehyde and methanol vapors in biotrickling filters under mesophilic and thermophilic conditions: Potential application in ethanol production
Published in Journal of the Air & Waste Management Association, 2022
Mitham Al-Faliti, Bruce Dvorak, Ashraf Aly Hassan
To control HAP emissions, the US EPA has identified the best available control technologies (BACTs) (USEPA 2016). The traditional technologies used to control emissions from ethanol plants are regenerative thermal oxidizers (RTOs) and water scrubbers (USEPA 2019). Both technologies require a considerable amount of energy and are costly to operate. In a personal communication with an ethanol plant director (Lyndon 2019), it was highlighted that the RTO maintenance costs ~$1 million per year. However, the average size of an RTO is ~18 MMBtu/h which will combust ~155 million standard cubic feet (SCF) of natural gas per year (Nester 2007). Concentrations of the VOCs in the waste gas stream are essential to identify the design and size of RTOs (Sorrels et al. 2017). The lower explosive limit (LEL) is a limit that defines the minimum concentration of that compound that can produce more energy than is needed to raise its temperature to be ignited (Sorrels et al. 2017). If a compound in the waste gas has a value higher than 50% of its LEL, it must be first diluted with air to meet the regulations (Sorrels et al. 2017). At a conservative price of $4.00 per 1000 SCF, a total cost of over 600,000 USD per year is required to operate an RTO (U.S. Energy Information Administration 2019). However, prices in the USA, and elsewhere in the world, can be higher than 4.00 USD per 1000 SCF. Catalytic thermal oxidizers (CTOs) are a similar technology to RTOs. However, CTOs treat VOCs and HAPs at lower temperatures than RTOs and use a catalyst to speed up the oxidation of VOCs to water and CO2 (USEPA n.d.). The cost of removing a pollutant based on styrene as the pollutant removed for the CTOs is ~ 2,974 $/ton removed (USEPA n.d.). Other than ethanol production, the combustion of biogas fuels can also produce harmful air emissions such as formaldehyde, styrene, and VOCs (e.g., Mustafi, Raine, and Bansal 2006; Pérez, Álvarez-Hornos, and Portune et al. 2015; Dobslaw et al. 2017; San-Valero et al. 2017; Dobslaw et al., 2019a). A study by Dobslaw et al. (2019a) has evaluated removing a crude gas mixture containing NO, NOx, NO2, CO, VOCs, and formaldehyde (Dobslaw et al., 2019a). The reactor used to perform the treatment consisted of a two-stage chemical scrubber with an optional biofilter operated at thermophilic conditions (55–60°C) (Dobslaw et al., 2019a). The chemical scrubber showed an efficiency of 95.7–97.2% in removing formaldehyde from the crude gas, and oxygen injection is important to allow for more efficient formaldehyde biodegradation (aerobic conditions) (Dobslaw et al., 2019a). The biofilter showed no treatment of the gases at thermophilic conditions (Dobslaw et al., 2019a).