Page 80 - Plant design and economics for chemical engineers

62 PLANT DESIGN AND ECONOMICS FOR CHEMICAL ENGINEERS

LOSS PREVENTION
The phrase loss prevention in the chemical industry is an insurance term where
the loss represents the financial loss associated with an accident. This loss not
only represents the cost of repairing or replacing the damaged facility and
taking care of all damage claims, but also includes the loss of earnings from lost
production during the repair period and any associated lost sales opportunities.
As noted in the previous section, there are numerous hazards associated
with chemical processing. The process designer must be aware of these hazards
and ensure that the risks involved with these hazards are reduced to acceptable
levels through the application of engineering principles and proven engineering
practice. In its simplest terms, loss prevention in process design can be summa-
rized under the following broad headings:

1. Identification and assessment of the major hazards.
2. Control of the hazards by the most appropriate means; for example, contain-
ment, substitution, improved maintenance, etc.
3. Control of the process, i.e., prevention of hazardous conditions in process
operating variables by utilizing automatic control and relief systems, inter-
locks, alarms, etc.
4. Limitation of the loss when an incident occurs.
Identification can be as simple as asking “what-if’ questions at design
reviews. It can also involve the use of a checklist outlining the normal process
hazards associated with a specific piece of equipment. The major weakness of
the latter approach is that items not on the checklist can easily be overlooked.
The more formalized hazard-assessment techniques include, but are not limited
to, hazard and operability study (HAZOP), fault-tree analysis (FTA), failure
mode-and-effect analysis (FMEA), safety indexes, and safety audits.

HAZOPS Study
The hazard and operability study, commonly referred to as. the HAZOP study,
is a systematic technique for identifying all plant or equipment hazards and
operability problems. In this technique, each segment (pipeline, piece of equip-
ment, instrument, etc.) is carefully examined and all possible deviations from
normal operating conditions are identified. This is accomplished by fully defin-
ing the intent of each segment and then applying guide words to each segment
as follows:

No or not-no part of the intent is achieved and nothing else occurs (e.g.,
no flow)
More-quantitative increase (e.g., higher temperature)
Less-quantitative decrease (e.g., lower pressure) , .
As well as-qualitative increase (e.g., an impurity)