Hazardous Material Ratings

4 Deadly—the slightest exposure to this substance could be life-threatening. Only specialized protective clothing should be worn when working with this substance. 

3 Extremely dangerous—serious injury could result from exposure to this substance. Do not expose any body surface to this material. Full protective measures should be taken. 

2 Dangerous—exposure to this substance would be hazardous to health. Protective measures are indicated. 

4 Flash point below 73°F—substance is very volatile, explosive, or flammable. Use extreme caution when handling or storing the substance. 

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Distillation. There is a large inventory of boiling liquid, sometimes under pressure, in a distillation column, both in the base and held up in the column. If a sequence of columns is involved, then, as discussed in Chap. 5, the sequence can be chosen to minimize the inventory of hazardous material. If all materials are equally hazardous, then choosing the sequence that tends to minimize the flow rate of nonkey components also will tend to minimize the inventory. Use of the dividing-wall column shown in Fig. 5.17c will reduce considerably the inventory relative to two simple columns. Dividing-wall columns are inherently safer than conventional arrangements because they lower not only the inventory but also the number of items of equipment and hence lower the potential for leaks. 

Refrigeration, like dilution, reduces the vapor pressure of the material being stored, reducing the driving force (pressure differential) for a leak to the outside environment. If possible, the hazardous material should be cooled to or below its atmospheric pressure boiling point. At this temperature, the rate of flow of a liquid leak will depend only on liquid head or pressure, with no contribution from vapor pressure. The flow through any hole in the vapor space will be small and will be limited to breathing and diffusion. 

A related concept to inherently safer design is user-friendly design designing equipment so that human error or equipment failure does not have serious effects on safety (and also on output or efficiency). While we try to prevent human errors and equipment failures, only very low failure rates are acceptable when we are handling hazardous materials, and, as this book has shown, it is hard to achieve them. We should, therefore, try to design so that the effects of errors are not serious. The follov,/-ing are some of the ways in which we can accomplish this ... 

Fatal accident rate Lost-time injury rate Capital cost of accidents Number of plant/community evacuations Cost of business interruption Cost of workers compensation claims Number of hazardous material spills (in excess of a threshold) Tonnage of hazardous material spilled Tonnage of air, water, liquid and solid effluent Tonnage of polluting materials released into the environment Employee exposure monitoring Number of work related sickness claims Number of regulatory citations and fines Ecological impact of operations (loss or restoration of biodiversity, species, habitats)... 

The dispersed phase should be the one that has the higher volumetric rate except in equipment subject to backmixing where it should be the one with the smaller volumetric rate. It should be the phase that wets the material of construction less well. Since the holdup of continuous phase usually is greater, that phase should be made up of the less expensive or less hazardous material. 

Studies of the incineration of liquid and solid wastes must determine the rates at which hazardous compounds are released into the vapor phase or are transformed in the condensed phase, particularly when the hazardous materials make up a small fraction of the liquid burned. We must be particularly concerned with understanding the effects of the major composition and property variations that might be encountered in waste incinerator operations—for example, fluctuations in heating value and water content, as well as phase separations. Evidence of the importance of variations in waste properties on incinerator performance has been demonstrated by the observation of major smges in emissions from rotary-kiln incinerators as a consequence of the rapid release of volatiles during the feeding of unstable materials into the incinerator. 

Park KS, Sorenson DL, Sims J. 1988. Volatilization of wastewater trace organics in slow rate land treatment systems. Hazardous Waste and Hazardous Materials 5 219-229. 

Safety. The MR is much safer than the MASR. (1) The reaction zone contains a much smaller amount of the reaction mixture (hazardous material), which always enhances process safety. (2) In case of pump failure, the reaction automatically stops since the liquid falls down from the reaction zone. (3) There is no need to filter the monolithic catalyst after the reaction has been completed. Filtration of the fine catalysts particles used in slurry reactors is a troublesome and time-consuming operation. Moreover, metallic catalysts used in fine chemicals manufacture are pyrophoric, which makes this operation risky. In a slurry reactor there is a risk of thermal runaways. (4) If the cooling capacity is insufficient (e.g. by a mechanical failure) a temperature increase can lead to an increase in reaction, and thus heat generation rate. 

Wang, L.K. and Wang, M.H.S., Decontamination of groundwater and hazardous industrial effluents by high-rate air flotation process, Proc. Great Lakes 1990 Conference, Hazardous Materials Control Research Institute, Silver Springs, MD, September 1990. 

Hazards surveys This can be as simple as an inventory of hazardous materials, or it can be as detailed as the Dow indexes. The Dow indexes are a formal rating system, much like an income tax form, that provide penalties for hazards and credits for safety equipment and procedures. 

Mitigation measures can also be passive safeguards, meaning that they require no human intervention and no engineered sensing and actuation system to work. Examples of passive mitigation measures are secondary containment systems, blast-resistant and fire-resistant structures, insulated or low-heat-capacity spill surfaces to reduce the rate of evaporation, and an increased distance between the hazardous materials and energies and the sensitive receptors. 

Seemingly inconsequential changes to a process, such as a slight increase in temperature, pressure, or flow rate, can lead to a major increase in hazards. Materials of construction also need to be considered. Many fires have been caused by the replacement of a material or part with what was assumed to be an "equivalent replacement."... 

De, AK Chaudhuri, B Bhattaehaijee, S Dutta, BK. Estimation of OH radical reaction rate eonstants for phenol and ehlorinated phenols using UV/H2O2 photo-oxidation. Journal of Hazardous Materials, 1999 64 (1), 91-104. 

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