Inherently safer design limitation

Know what safeguards are (or need to be) in place to prevent uncontrolled reactions from taking place, including how to avoid them altogether (inherently safer design/operations) and how to control them within safe limits (automatic controls, procedures, etc.). 

Substitution of an hazardous chemical is often an even more complex problem, in particular regarding the trade-off between inherently safer design and sustainable chemistry. Several examples are discussed in subsequent chapters. We thus limit our discussion here to a few aspects. Up until around the 1960s the Reppe process was employed for of synthesis of acrylic esters ... 

Plant designs should be based on a risk assessment that considers the process and the site in detail as well as all of the principles of inherently safer operation. Earlier decisions may limit the options in... 

Procedural controls, process controls, 98-99 Process controls, 96-100 active controls, 98 inherently safer approach, 97 mitigation techniques, 99 passive controls, 97-98 procedural controls, 98-99 safe operating limits, 99-100 Process definition, documentation, 102-104 Process design, documentation, 105 Process hazard analysis (PHA) risk assessment, 92-93 screening methods, 63 Process risk management decisions, documentation, 105-106... 

Most organic solids, metals, and some combustible inorganic salts can form explosive dust clouds. In order to have a dust explosion, certain elements are necessary (1) Particles of dust of suitable size, (2) A sufficient source of ignition energy, (3) A concentration of dust within explosive limits. If an explosive dust in air that meets the above criteria occurs in a process, an explosion should be considered inevitable. The process designer of inherently safer plants must take into account the possibility of dust explosions and design accordingly. 

But it must be emphasized again, that bursting disks and safety valves should always represent the last resort only. Instead, one should work towards a synthesis development which takes care of a significant distance between true reaction data under desired conditions and those limit values which correspond to the individual designs of relief systems. Such designs in the sense of safety barriers support the attempt to allow the performance of thermally inherent safer processes only. This way relief systems could be reduced in their purpose to what they actually should be a formally required installation to a vessel, which should never have to prove its efficiency. 

Continuous or semi-batch processes are usually inherently safer than batch processes. The applications of continuous processes are limited, but almost all processes can be designed to operate in a semi-batch mode. 

Despite the obvious importance of ISD, there has only been limited work for developing tools that support the assessment of IS. INSET was developed to promote IS principles, and contains a set of tools which support the adoption of IS principles into process development and design (Malm n et al., 1995 van Steen, 1996, Turney et al. 1997). Recently, an expert system that supports ISD by identifying safety issues and proposing inherently safer alternatives was reported (Palaniappan et al., 2002a 2002b). 

---