Inherently safer

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. 

Other Parasiticides. The parasiticides described below have a relatively limited usage owing to a narrow spectmm of antiparasitic activity or because of the introduction of inherently safer or more effective products. 

Trevor A KletZ/ D Sc / Senior Visiting Research Fellow, Depatiment of Chemical Engineering, Loughborough, University U.K. Fellow, American Institute of Chemical Engineers, Royal Academy of Engineers (U.K.), In stitution of Chemical Engineers (U.K.), and Royal Society of Chemlstiy (U.K.). (Inherently Safer Design)... 

PROCESS SAFETY INTRODUCTION INHERENTLY SAFER DESIGN AND OTHER PRINCIPLES... 

Inherently Safer and More User-Friendly Design. 26-5... 

Inherently Safer Design Rather than add on equipment to control hazards or to protect people from their consequences, it is better to design user-friendly plants which can withstand human error and equipment failure without serious effects on safety, the environment, output, and efficiency. This part is concerned with this matter. 

INHERENTLY SAFER AND MORE USER-FRIENDLY DESIGN... 

The principle ways of designing inherently safer plants and other ways or makiug plants user-friendly are summarized as follows, with examples (Kletz, Plant De.sign for Safety—A U.ser-Friendly Approach, Hemisphere, 1991). 

Intensification is the preferred route to inherently safer design, as the plants, being smaller, are also cheaper. 

The following actions are needed for the design of inherently safer and more user-friendly plants-. 

Such mishaps can be worse if the chemistiy is not fuUy understood. A chemical plant can be inherently. safer if knowledge of the chemistiy of the process and the reactive chemicals systems involved is used in its design. 

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. 

Select a process chemistry or synthesis route that is inherently safer. 

Select a process chemistry or synthesis route that is inherently safer (e.g., nontoxic, nonflammable materials, less severe operating condition)... 

Use inherently safer chemistry (e.g., when phosgene is cooled in a heat exchanger, consider use of an inert oil as the coolant rather than water as heat exchanger tubes may fail)... 

Use inherently safer equipment (e.g., jacketed vessels instead of tube heat exchangers)... 

Substitute or attenuate hazardous materials (inherently safer alternative)... 

Consider Inherently Safer Design alternatives (e.g., to withstand maximum upset conditions—temperature, pressure, flow)... 

Use less corrosive chemistry (inherently safer principles)... 

CCPS G-41. Inherently Safer Processes A Life Cycle Approach. American Institute of Chemical Engineers, Center for Chemical Process Safety, New York. 

Inherently Safer A system is inherently safer if it relies on the chemistry and physics (the quantity, properties and conditions of use of the process materials) rather than on control systems, interlocks, alarms and procedures to prevent incidents. 

It is recommended that flammability always be assessed first, since it is inherently safer to avoid flammable atmospheres than to avoid sources of ignition such as static electricity. If a flammable atmosphere cannot be avoided at all times, the system should be designed to minimize both the probability and consequences of ignition. In this chapter it is assumed that static electricity is the only source of ignition however, in practical situations all sources of ignition such as those described in [ 157] should be evaluated. 

Transfer of an active chemical agent in an inherently safer form (e.g. sulphur dioxide as sodium metabisulphite, chlorine as sodium hypochlorite). Generation of an active agent in this manner clearly reduces the inventory in use. 

Kletz, T.A. (1998) Process Plants A Handbook of Inherently Safer Design, Taylor and Francis Inc. 

Kletz, T.A. (1984) Cheaper, Safer Plants or Wealth and Safety at Work Notes on Inherently Safer and Simpler Plants, Institution of Chemical Engineers Loss Prevention Information Exchange Scheme - Hazard Workshop Module. 

The following should be considered in designing an inherently safer plant involving reactor systems ... 

---