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SAFETY AND LOSS PREVENTION
processes and equipment. The Institution of Chemical Engineers has published a book on
safety of particular interest to students of Chemical Engineering, Marshall and Ruhemann
(2000).
9.2. INTRINSIC AND EXTRINSIC SAFETY
Processes can be divided into those that are intrinsically safe, and those for which the
safety has to be engineered in. An intrinsically safe process is one in which safe operation
is inherent in the nature of the process; a process which causes no danger, or negli-
gible danger, under all foreseeable circumstances (all possible deviations from the design
operating conditions). The term inherently safe is often preferred to intrinsically safe, to
avoid confusion with the narrower use of the term intrinsically safe as applied to electrical
equipment (see Section 9.3.4).
Clearly, the designer should always select a process that is inherently safe whenever
it is practical, and economic, to do so. However, most chemical manufacturing processes
are, to a greater or lesser extent, inherently unsafe, and dangerous situations can develop
if the process conditions deviate from the design values.
The safe operation of such processes depends on the design and provision of engineered
safety devices, and on good operating practices, to prevent a dangerous situation devel-
oping, and to minimise the consequences of any incident that arises from the failure of
these safeguards.
The term “engineered safety” covers the provision in the design of control systems,
alarms, trips, pressure-relief devices, automatic shut-down systems, duplication of key
equipment services; and fire-fighting equipment, sprinkler systems and blast walls, to
contain any fire or explosion.
The design of inherently safe process plant is discussed by Kletz in a booklet published
by the Institution of Chemical Engineers, Kletz (1984) and Keltz and Cheaper (1998). He
makes the telling point that what you do not have cannot leak out: so cannot catch fire,
explode or poison anyone. Which is a plea to keep the inventory of dangerous material
to the absolute minimum required for the operation of the process.

9.3. THE HAZARDS
In this section the special hazards of chemicals are reviewed (toxicity, flammability and
corrosivity); together with the other hazards of chemical plant operation.

9.3.1. Toxicity
Most of the materials used in the manufacture of chemicals are poisonous, to some extent.
The potential hazard will depend on the inherent toxicity of the material and the frequency
and duration of any exposure. It is usual to distinguish between the short-term effects
(acute) and the long-term effects (chronic). A highly toxic material that causes immediate
injury, such as phosgene or chlorine, would be classified as a safety hazard. Whereas a
material whose effect was only apparent after long exposure at low concentrations, for
instance, carcinogenic materials, such as vinyl chloride, would be classified as industrial