Encyclopedia of Environmental Science and Engineering, Volume I and II

512

INDUSTRIAL HYGIENE ENGINEERING

INTRODUCTION

It can be said that the industrial or occupational physician

and nurse are in the front line of industrial health and the

contribution they make with regard to diagnosis, establish-

ment of causes, treatment and rehabilitation are of great

importance to the health of the workers. But once the

potential cause of ill health or discomfort is established it is

usually the engineer who is required to design out the prob-

lems. Thus the engineer has a most positive contribution to

make in the maintenance of good health amongst the work-

ing population. The engineer is in the forefront of industrial

medicine and as such can make as great a contribution as

the medical profession because he or she is in the position

to modify the industrial process, or to apply some environ-

mental control system to the workplace, such that workers’

exposure to physical, chemical or biological insults can be

minimised.

When discussing workplace pollution from airborne

materials such as dusts, fumes, gases, vapours and mists, it

is useful to first define the outcome of various degrees of

overexposure which may result from ineffective, faulty or

non-existent pollution controls. In simple terms these may

be considered under the categories shown below:

1) The stochastic effects, where the probability of

developing a disease increases with dose, as with

carcinogens or sensitizers.

2) The acute effects, characterized by rapid absorp-

tion and effect due to sudden exposure, typical of

asphyxiants.

3) The subacute effects, resulting from repeated

and extended exposures over a period of hours

or days, an example of which would be the early

symptoms of narcosis.

4) The chronic effects, resulting from continued

absorption over a long period of time, e.g., mate-

rials leading to fibrosis of the lung.

5) The combination of any of the above.

The effects of exposure of workers to heat, noise and

radiation also fall into the above categories. Not only will

the degree of control depend upon the potential hazard but

the requirement for back up and monitoring systems will, to

a great extent, be determined by the potential consequences

of failure of the control measures. This chapter will discuss

in further detail the engineering considerations in designing

control measures for workplace environments.

In designing control systems it is necessary to define

the objectives such that the alternative engineering options

can be seen in perspective. The basic techniques of work-

place control are: substitution of a less hazardous mate-

rial or process, segregation or enclosure of the operation,

suppression of emission, ventilation extraction at source,

ventilation dilution to reduce concentration in the general

atmosphere.

The success of the selected control method will be judged

by its ability to reduce personal risk by minimizing worker

exposure and absorption. Furthermore the control method

should remain effective and maintain the same degree of

protection over the working life of the process.

Unfortunately, failure and ineffectiveness of control

systems are only too well known and examples are common:

enclosures that are left open: ventilation systems that fall

into disrepair or are not used due to shopfloor objections to

noise, or cold draughts produced as a result of careless or

incompetent design; work procedures that are impossible

to follow; personal protection that cannot be worn for any

length of time. Many more examples could be cited but to

the unfortunate recipient failure to protect means a risk to

health irrespective of the reason.

Potential risk should be assessed by examining the pos-

sible results of failure of the control system. Where chronic

hazards exist an occasional transient failure may not be too

serious but in the case of sensitizers and carcinogens any

overexposure could have serious implications, and, in the

case of asphyxiants, failure could be fatal. Thus, in the case

of acute hazards the control system should be adequate to

prevent even momentary peaks above the control limit. On

the other hand, where there are no materials with serious

acute hazards, short excursions above a chosen standard

level may be permissible provided that the average dose is

controlled. Where potential failure could have serious con-

sequences then the engineering software specifications need

to be more stringent, i.e., there may be a need for built-in

redundancy and back-up controls. The interpretation of con-

trol standards and specifications should only be undertaken

by a competent industrial hygienist.

As the achievement of comfort is also an objective,

physiological and psychological factors should not be over-

looked. To allow for human factors in designing controls it

is necessary to move outside the realm of pure engineering.

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