Safe process

The starred items in the hazard tree are changes in process conditions that could develop into sources and lead to hazards. These items are identified in Table 14-1 in the order of their severity. 

Overpressure can lead directly to all three hazards. It can lead directly and immediately to injury, to fire or explosion if there is an ignition source, and to pollution if there is not enough containment. Therefore, we must have a very high level of assurance that overpressure is going to have a very low frequency of occurrence. 

Fire tubes can lead to fire or explosion if there is a leak of crude oil into the tubes or failure of the burner controls. An explosion could be sudden and lead directly to injury. Therefore, a high level of safety is required. 

Sources Associated with Process System Changes 

OverprvssLire Injury Fire/Explosion Pollution None Ignition Source Inadequate Containage 

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Some silica-containing additives such as glass and titanium dioxide lower the thermal stabkity of PVDE and should be used with caution. Processors should consult the resin producer about safe processing practice. 

D. A. Shapton and N. F. Shapton, eds.. Principles and Practices for the Safe Processing of Foods, Butterworth-Heinemann Ltd., Oxford, U.K., 1991. 

Liquid sterilants are known to corrode the metal parts of articles and instmments that are to be sterilized, although articles composed exclusively of glass or certain type of corrosion-resistant metal alloys can be safely processed. Because the degree of corrosion is related to length of exposure, many articles are merely disinfected in a shorter exposure time. Disinfection may be suitable for certain appHcations. The safety of using Hquid sterilants must be judged by a qualified microbiologist. 

The use of safe materials is vital for barrier appHcations, particularly for food, medical, and cosmetics packaging. SuppHers of specific barrier polymers can provide the necessary details, such as material safety data sheets, to ensure safe processing and use of barrier polymers. 

The PEEK resia is gray, crystalline, and has excellent chemical resistance T is ca 185°C, and it melts at 288°C. The unfilled resia has an HPT of 165°C, which can be iacreased to near its melting poiat by incorporating glass filler. The resia is thermally stable, and maintains ductiUty for over one week after being heated to 320°C it can be kept for years at 200°C. Hydrolytic stabiUty is excellent. The resia is flame retardant, has low smoke emission, and can be processed at 340—400°C. Crystallinity is a function of mold temperature and can reach 30—35% at mold temperatures of 160°C. Recycled material can be safely processed. Properties are given ia Table 16. 

CCPS G-29. Guidelines for Safe Process Operations and Maintenance. American Institute of Chemical Engineers, Center for Chemical Process Safety, New York. 

In nonindustrial settings, MCS substances are the cause of indoor air pollution and are the contaminants in air and water. Many of the chemicals which trigger MCS symptoms are known to be irritants or toxic to the nervous system. As an example, volatile organic compounds readily evaporate into the air at room temperature. Permitted airborne levels of such contaminants can still make ordinary people sick. When the human body is assaulted with levels of toxic chemicals that it cannot safely process, it is likely that at some point an individual will become ill. For some, the outcome could be cancer or reproductive damage. Others may become hypersensitive to these chemicals or develop other chronic disorders, while some people may not experience any noticeable health effects. Even where high levels of exposure occur, generally only a small percentage of people become chemically sensitive. 

Many examples of safe processing in micro reactors have been reported. Among them, the formation of the poisonous hydrogen cyanide is often mentioned [5], Rinard and Saha refer to the non-oxidative Degussa variant [174] of this synthesis [85], while a micro reactor has performed the oxidative formation of hydrogen cyanide [175] via the Andrussov process [176,177]. 

It has been shown, particularly for the latter reaction and for the ethylene oxide process, that micro reactors allow safe processing of otherwise hazardous oxidations [4, 26, 40, 42, 43, 84]. This is first due to the fact that the inner volume of micro reactors is small so that explosions also happen only on a micro scale . The... 

Safe processing was found experimentally in parallel with this theoretical fundament [115,116], both leading to further experimentation [9,82,117,118], Although the hydrogen/reaction is not of direct use itself, it stands as a prominent model reaction for other more valuable processes (see, e.g., [GP 2] and [GP 3]), for which benefits due to safe processing in novel explosive regimes are expected. 

In the elaboration of a safe process it is necessary to look for those synthetic routes which do not incorporate hazardous raw materials, solvents, and additives. This is unfortunately rarely achievable. Therefore, the best way to insure higher intrinsic safety is ... 

Processes can be divided into those that are intrinsically safe, and those for which the safety has to be engineered in. An intrinsically safe process is one in which safe operation is inherent in the nature of the process a process which causes no danger, or negligible danger, under all foreseeable circumstances (all possible deviations from the design operating conditions). The term inherently safe is often preferred to intrinsically safe, to avoid confusion with the narrower use of the term intrinsically safe as applied to electrical equipment (see Section 9.3.4). 

The design of inherently safe process plant is discussed by Kletz in a booklet published by the Institution of Chemical Engineers, Kletz (1984) and Keltz and Cheaper (1998). He makes the telling point that what you do not have cannot leak out so cannot catch fire, explode or poison anyone. Which is a plea to keep the inventory of dangerous material to the absolute minimum required for the operation of the process. 

Ozone is strongly endothermic (A(g) +142.2 kJ/mol, 2.96 kJ/g) and the pure solid or liquid materials are highly explosive. Evaporation of a solution of ozone in liquid oxygen causes ozone enrichment and ultimately explosion [1], Organic liquids and oxidisable materials dropped into liquid ozone will also cause explosion of the ozone [2], Ozone technology and hazards have been reviewed [3], a safe process to concentrate ozone by selective adsorption on silica gel at low... 

Supercritical C02 (scC02) is one of the most appealing easily recyclable solvents, allowing the design of environmentally safe processes. Supercritical C02 has properties similar to those of... 

An example of solid-phase microwave synthesis where the use of open-vessel technology is essential is shown in Scheme 4.10. The transesterification of /3-keto esters with a supported alcohol (Wang resin) is carried out in 1,2-dichlorobenzene (DCB) as a solvent under controlled microwave heating conditions [22], The temperature is kept constant at 170 °C, ca. 10 degrees below the boiling point of the solvent, thereby allowing safe processing in the microwave cavity. In order to achieve full conversion to the desired resin-bound /3-keto ester, it is essential that the methanol formed can be removed from the equilibrium [22]. 

Most examples of microwave-assisted chemistry published to date and presented in this book (see Chapters 6 and 7) were performed on a scale of less than 1 g (typically 1-5 mL reaction volume). This is in part a consequence of the recent availability of single-mode microwave reactors that allow the safe processing of small reaction volumes under sealed-vessel conditions by microwave irradiation (see Chapter 3). While these instruments have been very successful for small-scale organic synthesis, it is clear that for microwave-assisted synthesis to become a fully accepted technology in the future there is a need to develop larger scale MAOS techniques that can ultimately routinely provide products on a multi kg (or even higher) scale. 

For example, a traditional checklist is, by definition, based on the process experience the author accumulates from various sources. The checklist is likely to provide incomplete insights into the design, procedural, and operating features necessary for a safe process. The what-if part of the analysis uses a team s creativity and experience to brainstorm potential accident scenarios. However, because the what-if analysis method is usually not as detailed, systematic, or thorough as some of the more regimented approaches (e.g., HAZOP study, FMEA), use of a checklist permits the PrHA team to fill in any gaps in their thought process. 

The first key factor, energy, is involved in the production of any chemical. Design of a safe process requires an understanding of the inherent energy (exothermic release/endothermic absorption) during chemical reactions. This information can come from the literature, from thermochemical calculations, or from proper use of testing equipment and procedures. The potential pressure that may be developed in the process is also a very important design consideration. 

This section discusses how a runaway reaction occurs and lists some of the process deviations that can lead to such a runaway. Equipment for identifying potentially hazardous process steps is reviewed, and general principles for inherently safe process design are given. 

The first example involves flammability issues that are not specifically covered in this Guidelines book. However, the discussion here is highly important for safe process design considerations and represents a good example of the problems of scale-up from test data. Runaway reactions may indeed result in the production of flammable gases so an understanding of the scale-up problems is critical. 

The scope of this book includes several aspects of safe process design and operation, such as the choice of reactor type, safe operating conditions, and the selection of protective systems, primarily related to chemical reactivity. However, even in a process plant where these aspects have been carefully considered and thoroughly applied, there are still numerous events that can occur and can lead to hazardous incidents. Examples of such events are ... 

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