safety engineering modules

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MODULE TITLE : SAFETY ENGINEERING

TOPIC TITLE : AN INTRODUCTION TO SAFETY ENGINEERING

LESSON 3 : INDUSTRIAL SAFETY TERMINOLOGY

SE - 1 - 3

Teesside University 2011


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Published by Teesside University Open Learning (Engineering)

School of Science & Engineering

Teesside University

Tees Valley, UK

TS1 3BA

+44 (0)1642 342740

All rights reserved. No part of this publication may be reproduced, stored in a

retrieval system, or transmitted, in any form or by any means, electronic, mechanical,

photocopying, recording or otherwise without the prior permission

of the Copyright owner.

This book is sold subject to the condition that it shall not, by way of trade or

otherwise, be lent, re-sold, hired out or otherwise circulated without the publisher's

prior consent in any form of binding or cover other than that in which it is

published and without a similar condition including this

condition being imposed on the subsequent purchaser.


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________________________________________________________________________________________

INTRODUCTION________________________________________________________________________________________

There are a number of terms which are in common use in safety engineering and

which you will meet in this lesson. In everyday language many of these terms

are virtually synonymous (have the same meaning), but in the world of safety

engineering they have quite specific meanings. It is important that you are

familiar with these terms and understand their meanings when you meet them.

Try to memorize as many of these words as possible at this stage. To help you

to do this, there are some Self-Assessment Questions included in the body of

the lesson.

In the second part of this lesson we shall be examining one of these terms

"risk" in more detail.

________________________________________________________________________________________

YOUR AIMS________________________________________________________________________________________

At the end of this lesson you should be able to:

explain the meaning of some of the common terms used in industrial

safety engineering

understand how the term 'risk' is applied within an engineering

system.

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Teesside University Open Learning(Engineering)



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________________________________________________________________________________________

STUDY ADVICE________________________________________________________________________________________

We strongly recommend that you memorise as many as possible of the terms in

the first part of the lesson. To help you to do this, spend as much time as

possible on the first set of Self-Assessment Questions.

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________________________________________________________________________________________

A GLOSSARY OF INDUSTRIAL SAFETY TERMINOLOGY IN COMMON AND

RECOMMENDED USAGE________________________________________________________________________________________

NOTE: Terms in italics are defined more fully elsewhere in this glossary.

HAZARD AND RISK

Hazard A state or condition having the potential

to cause a deviation from uniform or

intended behaviour which, in turn, may

result in damage to property, people or

the environment. For example, a

chemical process can realize its potential

through, for instance, fire or explosion

(catastrophically) or by corrosion

(insidiously).

It is neither desirable nor usuallypracticable to confidently rank or

measure a hazard in terms of size or

severity.

Risk The time-related, or location-related

likelihood of a hazard actually resulting

in an undesired event. Risks can be

quantitatively expressed in terms of

probability or frequency. (We will be

examining these terms more fully later in

this lesson.)

Risk Assessment This includes value judgements

concerning the significance of the risk

measurement results.

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Social Risk The risk to a group of people exposed to

a major hazard. This is usually

quantified on a F - N curve (see earlier

lesson). Societal risk can be more

accurately defined geographically if such

factors as distance, blast effects, gas

concentration and wind characteristics

are known or predictable.

Residual Risk The element of risk remaining after all

economically acceptable improvements

have been made.

CONSEQUENCES

Explosion A mechanically, or chemically, generated

rapid release of energy, which in turngenerates a blast (or shockwave)

capable of causing considerable damage

due to the velocity of pressure pulses

transmitted from the explosion.

(Particular types of explosion will be

identified later in the course.)

Explosion Pressure A term used to quantify the effects of an

explosion the pressure developed

above atmospheric pressure at a specific

receptor, e.g. a brick wall or a storage

tank.

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Overpressure This term is applied to the additional

internal pressure inadvertently arising

within equipment in excess of its design

pressure.

Fire A combustion process which generates

heat, smoke or flame, or any

combination of these.

Upper and Lower The concentrations of a flammable

substance in air or oxygen above or

below which, respectively, combustion

will not be sustained.

Fire Prevention Measures adopted to prevent an outbreak

or escalation of fire in a particular

location.

Fire Protection Design features, systems or equipment

(e.g. a sprinkler installation) which

minimise damage from fire in a

particular location.

Toxicity The ability of a toxic (poisonous)

substance, when absorbed by living

tissue (either ingested or via the skin), to

cause injury or destroy life.

Carcinogen A substance capable of causing cancer.

Asphyxiation Danger to, or termination of, life due to a

deficiency of oxygen.

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Flammability Limits


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Threshold and There are numerous categories of these,

each specific to a time-related human

exposure to toxic substances. They are

used to regulate the proximity of workers

to materials of known toxic effects.

RELEASE AND DISPERSION

Release The unintentional escape of a hazardous

substance or of energy (e.g. heat and/or

pressure) from a containment system,

usually due to equipment breakdown or a

control logic failure. There are various

types of release, including:

instantaneous release (i.e. of a

finite quantity of material)

continuous release (i.e. over a

prolonged period)

jet release

pinhole release.

Pool Evaporation Pool evaporation of a spilled volatile

liquid is a calculable phenomenon.

Burning Rate The burning rate of a flammable vapour

is also calculable.

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Exposure Limits


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Flashing Flow The behaviour, upon release, of a

superheated liquid, part of which

"flashes off" thereby creating a two-

phase flow of liquid and vapour/gas.

Flash Fraction The portion of a superheated liquid that

will vaporize upon release to the

atmosphere.

Dispersion The mode of integration and dilution,

usually in the environment, when a

hazardous fluid is discharged.

Gas Cloud A generic term which is self-explanatory,

but which usually needs more precise

definition according to whether the

released material is of higher or lower

density than the surrounding air (i.e.

"dense" or "buoyant").

Plume A gas cloud resulting from a continuous

release.

Weather Category An index system denoting the extent of

air turbulence and thermal stability. It is

an influencing factor in the safe dispersal

of flammable or toxic discharges.

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ASSESSMENT TECHNIQUES AND CRITERIA

Loss Prevention A systematic, often rigorous, procedure

aimed at the prevention of incidents, or

the estimation and minimising of their

consequences. All objectives and some

of the most useful techniques are

covered in this course.

Hazard Analysis A term which should be confined to the

further and quantitative assessment of

hazards which have already been

identified and warrant examination of

size, frequency and consequences. This

approach is consistent with the accepted

philosophy that if a specific potential

hazard cannot be eradicated (e.g. by

designing-out), then it is necessary toassess the level of risklikely to result.

Site Safety Assessment The incisive appraisal of all facets of

equipment integrity and safe working

behaviour within a total work area (e.g.

a complete factory). This includes

management response to the maintenanceof acceptable safety standards. It is

invariably conducted at long intervals by

a competent, independent outside body or

consultant.

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Safety Audit A critical review, at (typically) annual

intervals, of a selected part of a total

operating facility (e.g. a plant unit,

internal emergency team, fail-safe

control functions). It is usually

conducted internally.

Checklist A relatively frequent, simple and rapid

endorsement of the satisfactory (but

usually visual) condition of plant items

and safety equipment.

Safety or Hazard These are terms of wide interpretation,

sometimes implying site assessment

standards but more often confined to a

search for potential hazards.

Safety Case A term, introduced more recently, which

describes a fully documented justification

for a proposed or existing hazardous

installation. It is sufficiently compre-

hensive to include selective quantitative

hazard analyses and emergency plans,

and is used in conjunction with the

Control of Major Accident Hazards

(COMAH) Regulations 1999.

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Review/Survey


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Probability A dimensionless number within the

range 0 1 representing:

(a) the probabil ity of a particularoutcome from a specified event

(e.g. success or failure of an action)

(b) the probability of a particular state

or condition existing at a specified

time (e.g. equipment availability or

non-availability).

Reliability Since "probability", in a safety context,

usually implies "probability of failure or

of a failed state", this term can be

regarded as the opposite; that is, the

probability that a required system or

individual will respond predictably

upon demand at the required point in

time under defined conditions.

Frequency The number of occurrences of a

specified event over a time period of

interest (usually a year).

Failure A term that is incorporated into severalspecific applications, the meanings of

which are self-explanatory, e.g.

failure mode

fail to danger fault

failsafe

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common cause failure: failure of

more than one protective device or

system attributable to the same

cause. (This expression is of

particular interest to the processing

industries. For example, a failure of

the public electricity or cooling

tower supplies can cause a

shutdown of several facilities

simultaneously.)

common mode failure: resultant

identical failure patterns in

components or systems occurring

simultaneously due to a common

cause. For example, overheating of

a series of pumps.

Criterion A standard of safety performance to

which a measured performance may be

compared.

Target Fatal Accident Rate The number of deaths recorded or

predicted within a prescribed group in a

stated environment during 108 hours of

exposure. An example of this can be

obtained from calculations based on

1000 chemical plant operators working

for 40 hours per week for 50 weeks a

year, for a working lifetime of 50 years.

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(plural: criteria)


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Fatal Accident Rate (F.A.R.) The number of deaths recorded or

predicted per year.

Now do the first set of Self-Assessment Questions on pages 13 to 15.

Complete these questions before moving on to the next part of the lesson.

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________________________________________________________________________________________

SELF-ASSESSMENT QUESTIONS________________________________________________________________________________________

1. Match each term with one of the brief definitions given below.

1 Hazard 2 Societal risk 3 Explosion pressure

4 Fire prevention 5 Fire protection 6 Residual risk

7 Toxicity 8 Release

A the ability of a poisonous substance to cause injury or death

B the unintentional escape of a hazardous substance or of energy from a

containment system

C a state or condition having the potential to cause a deviation from

uniform or intended behaviour which may result in damage to

property, people or the environment

D the element of risk remaining after improvements have been made

E design features, systems or equipment intended to minimise damage

from fire

F measures intended to avert the outbreak of fire in a particular location

G the pressure developed above atmospheric pressure resulting from an

explosion

H risk to a group of people exposed to a major hazard

Your answer A_____ B_____ C_____ D_____ E_____

F_____ G_____ H_____

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2. Which of the following do you think best defines the term "risk" in an

industrial safety context:

(a) the element of risk remaining after all economically acceptable

improvements have been made

(b) a condition which is likely to cause damage to property

(c) the likelihood of an undesired event occurring which can be

expressed in terms of its size and severity

(d) the likelihood of an undesired event occurring which can be

expressed in terms of probability or frequency?

3. Which of the following do you think best defines the term "loss

prevention":

(a) the total elimination of all potential hazards

(b) the assessing of how an individual or system will respond in the

event of a major incident

(c) a systematic procedure aimed at either the prevention of incidents or

the estimation and minimising of their consequences

(d) the quantitative assessment of hazards based on the notion that it is

not possible to eliminate all potential risks?

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4. Give brief definitions for the following terms:

(a) dispersion

(b) plume

(c) explosion

(d) safety audit

(e) criterion

(f) upper and lower flammability limits.

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________________________________________________________________________________________

ANSWERS TO SELF-ASSESSMENT QUESTIONS________________________________________________________________________________________

1. A 7 B 8 C 1 D 6

E 5 F 4 G 3 H 2

2. (d)

3. (c)

4. Check your answers against the definitions given in the lesson.

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________________________________________________________________________________________

CATEGORIES OF RISK________________________________________________________________________________________

On page 3 we gave a brief definition of the term "risk". We will now look

more closely at the various categories of risk which could arise within an

engineering context.

There are two main categories of risk:

risks to life (site personnel and/or the general public)

risks to plant and profits.

RISKS TO LIFE

Risks to life can be sub-divided into two main groups.

1. 'Ordinary' Risks

These are common to all plants and arise principally from human activity

on or around the plant. Examples include:

falling off the structure

tripping over obstacles

impact by falling objects

contact with moving parts of equipment

physical operations such as lifting, scaffolding, flexing or carrying

out maintenance.

These risks are, of course, applicable only to plant personnel and not to

the general public.

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2. 'Process' Risks

These vary from plant to plant, the main classes of risk being:

fire or explosion due to emission of flammable material

emission of toxic or corrosive materials

discharge of hot scalding fluids

discharge of cold sub-zero fluids

blast ef fects or project iles ar is ing f rom equipment

rupture/fragmentation

asphyxiation risks.

Thus, process risks can arise only in the event of loss of containment of

the plant inventory and the general public as well as plant personnel can

be at risk.

RISKS TO PLANT AND PROFITS

These risks, which are concerned with damage to the plant, or with plant

unavailability for other reasons, can also be conveniently classified into two

main groups.

1. Risks due to incidents where there is also a risk to life

The main risks falling into this category are some of the "process risks"

previously mentioned, which lead either to plant unavailability in their own

right (e.g. equipment rupture, fire, explosion) or to a plant shutdown pending

an enquiry (e.g. toxic release or other dangerous incidents).

Some of the "ordinary risks" to life previously mentioned may sometimes also

call for a plant shutdown pending investigations.

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2. Risks due to incidents where there is no risk to life

The risks falling into this category are purely operational risks such as

equipment breakdown or unavailability

blockages of equipment or pipework

fouling of equipment.

Now attempt the second set of Self-Assessment Questions on page 20.

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________________________________________________________________________________________

SELF-ASSESSMENT QUESTIONS________________________________________________________________________________________

These Self-Assessment Questions cover the material on pages 17 to 19.

5. (i) If, as a result of identifying the likelihood of a particular hazard

occurring, a change to a system is decided upon, should you

immediately:

(a) record the hazard, and action taken, in the plant records for

future reference

(b) move on to search for other possible hazards

(c) re-examine the system in its changed condition for any

new problems which could thereby arise

or (d) sign-off the study as completed?

(ii) Now list the four actions above in what you consider to be a logical

order.

6. Categorize, as you see fit, the following events into the "risk table" or

matrix on page 21.

(a) falling into an excavation

(b) extinction by high winds of a flare-stack pilot flame

(c) a runaway fork-lift truck

(d) lighting a welding torch in a 'no-smoking' area

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(e) escape of refrigerant from an insulated storage vessel

(f) using scaffolding with toe-boards missing

(g) blockage of feed to an oil-fired heater due to cold climate

(h) ignition of flammable solvent by static discharge due to breakage of

earthing conductor

(i) leakage of ammonia from a high-pressure pipe joint

(j) bearing failure in an air compressor

Your Answer

'ORDINARY' RISK 'PROCESS' RISK

RISKTO

LIFE

NO

RISK

TO LIFE

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________________________________________________________________________________________

ANSWERS TO SELF-ASSESSMENT QUESTIONS________________________________________________________________________________________

5. (i) (c)

(ii) (c), (b), (a), (d).

6. 'ORDINARY' RISK 'PROCESS' RISK

RISK

TO (a) (c) (f)(d) (e)

LIFE (h) (i)

NO

RISK (j) (b) (g)

TO LIFE

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________________________________________________________________________________________

SUMMARY________________________________________________________________________________________

This lesson has covered the more important aspects of safety language, a vital

step towards avoiding misinterpretations and misunderstandings which are

themselves potential sources of hazards.

You have also now been introduced to the disciplined manner in which causes

and effects of deviant occurrences need to be handled, and the scope of these

risks which prevail within industrial activities.

We are now able to consider how human awareness and response to hazard

identification may best be improved.

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