Physical hazards explosive limits

Tlie remainder of tliis cliapter provides information on relative physical properties of materials (flash point upper and lower explosive limits, tlueshold limit values, etc.) and metliods to calculate tlie conditions tliat approach or are conducive to hazardous levels. Fire liazards in industrial plants are covered in Sections 7.2 and 7.3, and Sections 7.4 and 7.5 focus on accidental explosions. Sections 7.6 and 7.7 address toxic emissions and liazardous spills respectively. tliese latter types of accident frequently result in fires and explosions tliey can cause deatlis, serious injuries and financial losses. 

In recent years, there has been increasing emphasis placed on the health effects of chemical exposures. However, as has been frequently noted, health effects are much more difficult to quantitatively characterize than most physical safety parameters. It is straightforward to define with reasonable accuracy a number of physical hazards, such as the upper and lower explosive limits of the vapors of a flammable material. However, the exposure levels (see Figure 4.16, taken from the Federal Register Vol. 53, No. 109, June 7, 1988, p. 21342) which will cause a given physiological effect in humans are not nearly as precise, especially if the effect of interest is delayed or is due to prolonged exposure to low levels of a toxic material. 

Database of over 10,000 chemicals and synonyms, including DOT Guide information, and physical properties such as flash point, lower explosion limit, and boiling point, including the information contained in the 1997 NIOSH Pocket Guide to Chemical Hazards, the 2000ERG, and other sources. 

Physical hazards are defined as the types of hazards that can cause harm to a woiker from an external source. Types of physical hazards are loud noise (equipment), temperature extremes (working in personal protective equipment), radiation (exposures to the infrared or gamma rays), chemical bum (acids or caustics), fire, and explosions. Other physical hazards include, but are not limited to, slips and falls, exposed machinery because of improper guarding, live electrical circuits or conductors, equipment moving about on site, confined spaces, and falling objects. 

A substance is a hazardous chemical if it is a physical hazard or a health hazard . A flammable or explosive liquid is a physical hazard . A flammable liquid means any liquid having a flash point below 110°F (37.8°C), except any mixture having components with flash points of 100°F (37.8°C) or higher, the total of which make up 99% or more of the total volume of the mixture . Health hazard means a chemical for which there is statistically significant evidence based on at least one valid study that acute or chronic health effects may occur in exposed employees . Hexane and all the solvents listed in Table 13.10.3 would require a MSDS, since all are flammable liquids (physical hazards) as defined by OSHA and/or possible health hazards because all, except hexane isomers, have an U.S. OSHA PEL. However, hexane isomers have an American Conference of Industrial Hygienist (ACGIH) dneshold limit value (TLV), which many states and countries enforce as a mandatory standard. 

The physical explosion is treated here. If it is followed by a fireball (vid. Sect. 10.6.2.1) the following may be assumed if 36 % or more of the liquid is vaporized on pressure relief, the total released mass of fuel contributes to the fireball. For hazard assessments it is reasonable to suppose that three times the mass vaporized by depressurization (upper limit 100 %) partakes in the fireball [37]. 

Because of the large restricted area around the facilities and the remote location of the site, no industrial facility accidents are credible. The hazards associated vrith military accidents (i.e., expiosions, aircraft crash) are considered separately in the discussions of Aircraft Impacts, Chemical/Toxic Releases, External Explosions, and Missiles. Accidents in adjacent facilities in TA-V, such as the adjacent reactor fadlities, could have limited impact on the HCF as those faciiities are in separate buildings or physically separated from the HCF in an adjoining building. The nuciear faciiities have been designed to prevent accidents with the hazardous material in one faciiity from affecting the material in another facility. Thus, the impact of those adjacent faciiities on the HCF would likely be the same or less than External Fires. 

The approach used for the estimation of loss of life in floods shows considerable resemblance to the approach that is used in the Dutch major hazards policy. In both cases, the probability of a critical event (loss of containment or flood) is estimated using fault tree analysis, after which the physical effects associated with that critical event are considered (using e.g. dispersion or flood propagation models) and related to mortality estimates (using dose-response functions or flood mortality functions). But while the potential for evacuation is often limited when it comes to explosions or toxic releases, it could be significant when it comes to floods. 

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