PROCESS CONTROL AND PLANT SAFETY

Accidents in chemical plants make headline news, especially when there is loss of life or the general public is affected in even the slightest way. This increases the public’s concern and may lead to government action. The terms hazard and risk are defined as follows:

• Hazard. A potential source of harm to people, property, or the environment
• Risk. Possibility of injury, loss, or an environmental accident created by a hazard Safety is the freedom from hazards and thus the absence of any associated risks. Unfortunately, absolute safety cannot be realized.
  

The design and implementation of safety systems must be undertaken
with a view of two issues:

• Regulatory. The safety system must be consistent with all applicable codes and standards as well as “generally accepted good engineering practices.”
• Technical. Just meeting all applicable regulations and “following the crowd” does not relieve a company of its responsibilities. The safety system must work.
  

The regulatory environment will continue to change. As of this writing, the key regulatory instrument is OSHA 29 CFR 1910.119 that pertains to process safety management within plants in which certain chemicals are present.

In addition to government regulation, industry groups and professional societies are producing documents ranging from standards to guidelines. Instrument Society of America Standard S84.01, “Application of Safety Instrumented Systems for the Process Industries,” is in draft form at the date of this writing. The Guidelines for Safe Automation
of Chemical Processes from the American Institute of Chemical Engineers’ Center for Chemical Process Safety (1993) provides a comprehensive coverage of the various aspects of safety, and, although short on specifics, it is very useful to operating companies developing their own specific safety practices (that is, it does not tell you what to do, but it helps you decide what is proper for your plant).

The ultimate responsibility for safety rests with the operating company; OSHA 1910.119 is clear on this. Each company is expected to develop (and enforce) its own practices in the design, installation, testing, and maintenance of safety systems. Fortunately, some companies make these documents public. Monsanto’s Safety System Design Practices was published in its entirety in the proceedings of the International Symposium and Workshop on Safe Chemical Process Automation, Houston, Texas, September 27–29, 1994 (available from the American Institute of Chemical Engineers’ Center for Chemical
Process Safety).