Safety inherent

Industrial processes are prone to hazardous or unexpected events. In their paper, Nicholas D. Anastas and John C. Warner wrote, Hazard should be considered as a design flaw and eflorts need to be made in the designing phase to minimize or eliminate it (2005). Hazards may arise from many factors, and they manifest themselves in various forms. These various hazardous events could be external or internal fire, confined or unconfined explosion, noxious gas release, pollution, moving object hazard, etc. (USCSHI, 2000). The description of these events and their consequences are listed later in this chapter. 

External fire. May be prompted by flammable gas or vapor liquid, solid, metal, wood, or waste material pyrophoric material and presence of ignition source such as sparks, static, friction, hot spots, welding, lightning, auto ignition, or furnace. Immediate consequence engulfment, thermal radiation, fire damage, smoke, domino effect (where one incident is the primary cause for several other incidents). 

Internal explosion (inside equipment). May be prompted by uncontrolled reaction, equipment testing, filling, purging, or physical overpressure. Immediate consequence equipment damage, missile/fragment, structural damage. 

Unconfi.ned explosion, such as VCE (vapor cloud explosion), gas explosion, or detonation. May be prompted by flammable gas or vapor liquid, solid, dust, mist, oxygen, halogen or explosive or unstable compound. Immediate consequences missile, noise, light, domino effect, fumes/gases. 

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The development section serves as an intermediary between laboratory and industrial scale and operates the pilot plant. A dkect transfer from the laboratory to industrial-scale processes is stiH practiced at some small fine chemicals manufacturers, but is not recommended because of the inherent safety, environmental, and economic risks. Both equipment and plant layout of the pilot plant mirror those of an industrial multipurpose plant, except for the size (typically 100 to 2500 L) of reaction vessels and the degree of process automation. 

A more recent concept which could have significant impact on future designs is that of inherent safety (12). This basic principle states that what is not there cannot be blown up or leak into the environment. Thus, the idea is to avoid the hazard in the first place. 

Minimize inventory to the extent feasible. Expected benefits from minimum inventory may be offset by hazards resulting from more frequent and smaller shipments. The relative hazards should be reviewed (Englund, Design and Operate Plants for Inherent Safety—Part 1, Chem. Eng. Prog., vol. 87, no. 2, March 1991, pp. 85-91). 

Inherent safety Inventory reduction Fewer chemicals inventoried or fewer in process vessels. Chemical substitution Substitute a less hazardous chemical for one more hazardous. Fr ocess attenuation Use lower temperatures and pressures. 

Understanding the chemistry of the process also provides the greatest opportunity in applying the principles of inherent safety at the chemical synthesis stage. Process chemistry greatly determines the potential impact of the processing facility on people and the environment. It also determines such important safety variables as inventory, ancillary unit operations, by-product disposal, etc. Creative design and selection of process chemistry can result in the use of inherently safer chemicals, a reduction in the inventories of hazardous chemicals and/or a minimization of waste treatment requirements. 

Storage and receiving are activities that can greatly contribute to a safe and economic operation. It is here that quality control can be achieved at minimal cost. Label verification and other quality assurance measures can increase the confidence level that the correct chemicals have arrived, thereby potentially circumventing the use of wrong chemicals. Wrongly shipped chemicals can be returned to the manufacturer with minimal or no cost to the batch operation owner. As with all processes and activities it is of great importance to apply the principles of inherent safety, in particular the minimization and attenuation principles (CCPS G- 41). 

Kletz repeated the Jubilee Lecture twice in early 1978, and it was subsequently published (Kletz, 1978). In 1985 Kletz brought the concept of inherent safety to North America. His paper, Inherently Safer Plants (Kletz, 1985), won the Bill Doyle Award for the best... 

Hazards can be reduced or eliminated by changing the materials, chemistry, and process variables such that the reduced hazard is characteristic of the new conditions. The process with reduced hazards is described as inherently safer. This terminology recognizes there is no chemical process that is without risk, but all chemical processes can be made safer by applying inherently safer concepts. This book occasionally uses the term inherent safety this does not mean absolute safety. 

Transportation should be considered when assessing risks associated with planned or existing plants. The design of new chemical processing units should include at the earliest opportunity a qualitative or quantitative risk assessment of the whole system including production, use, and transportation in order to minimize overall risk. A brief discussion of the inherent safety aspects of transportation is included in Chapter 5. 

On the other hand, Mary, a research process development engineer, does not consider Joe s system to be inherently safer, because a truly inherently safer system would not require an interlock at all. The process uses flammable materials and operates at elevated pressure. Mary, looking at the entire process, would only consider it to be inherently safer if the flammable materials were eliminated or the process was operated at ambient pressure. Mary is considering the inherent safety characteristics of the entire process, rather than a single interlock system. 

It is never too late to consider inherently safer alternatives. Major enhancements to the inherent safety of plants which have been operating for many years have been reported (CCPS, 1993a Wade, 1987 Carrithers et al., 1996)... 

In many cases, the inherent safety advantages of one process are clear when compared with alternatives. One or more hazards may be significantly reduced, while others are unaffected or only marginally increased. For example, aqueous latex paints are clearly inherently safer than solvent based paints, although there are applications where the increased performance of solvent based paints justifies their use, with the appropriate layers of protection. 

McQuaid (1991), CCPS (1993a), and Hendershot (1995a) review a number of specific examples of inherent safety tradeoffs. These include ... 

Deciding among a number of process options having inherent safety advantages and disadvantages with respect to different hazards can be quite difficult. The first step is to understand thoroughly all hazards associated with the process options. Process hazard analysis and evaluation techniques are appropriate tools (CCPS, 1992). These include ... 

The combination of several unit operations into a single piece of equipment can eliminate equipment and simplify a process. There may be inherent safety conflicts resulting from this strategy (see Section 2.4). Combining a number of process operations into a single device increases the complexity of that device, but it also reduces the number of vessels or other pieces of equipment required for the process. Careful evaluation of the options with respect to all hazards is necessary to select the inherently safer overall option. 

Similarly, hazardous raw material storage should also be minimized, with greater attention being given to just in time supply. Inventory reduction lowers inventory costs, while increasing inherent safety. In determining appropriate raw material inventories, the entire raw material supply chain must be considered. Will the supplying plant have to increase inventories to provide just in time service, and will... 

Basic process chemistry using less hazardous materials and chemical reactions offers the greatest potential for improving inherent safety in the chemical industry. Alternate chemistry may use less hazardous raw material or intermediates, reduced inventories of hazardous materials, or less severe processing conditions. Identification of catalysts to enhance reaction selectivity or to allow desired reactions to be carried out at a lower temperature or pressure is often a key to development of inherently safer chemical synthesis routes. Some specific examples of innovations in process chemistry which result in inherently safer processes include ... 

The chemistry of side reactions and by-products may also offer opportunities for increasing the inherent safety of a process. For example, a process involving a caustic hydrolysis step uses ethylene dichloride (EDC 1,2-dichloroethane) as a solvent. Under the reaction conditions a side reaction between sodium hydroxide and EDC produces small but hazardous quantities of vinyl chloride ... 

Rogers and Hallam (1991) provide other examples of chemical approaches to inherent safety, involving synthesis routes, reagents, catalysts and solvents. 

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