A2 Science In Society 3.5
Teacher Notes
Introduction
This activity is based on material drawn from the HSE report
called The tolerability of risk from nuclear power station. The
full report can be downloaded here:
http://www.hse.gov.uk/nuclear/tolerability.pdf. Despite its
age, the report is still interesting.
Note that there is no need to download the report. Students
are not expected to read it. All the information needed is
presented in the PowerPoint presentation or in the activity
sheet.
Before students start on the activity you might want to
rehearse the key ideas about risk introduced in the AS
Science in Society course and make sure that students have
made sense of the boxes on pages 147 and 149 of the A2
textbook.
Guide the students through the activity with the help of the
presentation. At each stage give students the opportunity to
answer the questions – working in groups or individually, as
well as discussing answers in the class.
Commentary and suggested answers
1 Suggest reasons why there was then [at the time of the
Sizewell enquiry] a view that discussion of risks should be
left to experts.
Many experts believed that the quantification of risks is
too uncertain and too difficult a matter for people
generally to grasp. Others argued that most ordinary
people only wish to believe that there is no risk at all from
industrial activities and are not interested in finding out
what exactly the risks are. There was also the concern
that public discussion of risk would provokes objections to
things that people are not really bothered about.
2 Why is it no longer acceptable to ‘leave it to the experts’?
The public lost faith in the ‘experts’ in the nuclear industry
when it discovered the extent that mishaps and serious
accidents had been covered up. In other areas the
‘experts’ have disagreed or got it wrong as in the disputes
of BSE, MMR vaccination and GM crops.
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How science works
Ga Everything we do carries a certain risk.
New technologies and processes based on
scientific advances often introduce new
risks.
Gb Risk is a measure of the probability of
harm in a given situation.
Gc We can assess the size of a risk by
counting the number of instances of harm in
a representative sample of cases. This
estimate will be more accurate if the sample
size is large, and if instances of harm can
be easily and accurately detected. If the
probability is very low, it can be very difficult
to get an accurate estimate.
Gd The perceived risk of an activity is often
quite different from the actual measured
risk. We tend to overestimate the risk of:
unfamiliar activities (relative to more
everyday ones); imposed activities (relative
to freely chosen ones); invisible or unseen
hazards whose effects are not immediately
apparent (such as ionizing radiation, or
environmental pollutants).
Ge Several factors can influence a person’s
willingness to accept a specific risk. Most
people are more willing to accept a process
or situation that has some risk if they get
direct benefit from it and if they choose it
voluntarily rather than having it imposed.
Gf To make an informed decision about the
management of a given risk, we need to
take account both of the probability of the
event occurring, and the seriousness of the
consequences if it did. This is particularly
difficult in the case of events of very low
probability, but with very serious
consequences if they occur.
Gg It is difficult to assess the risk of a new
technology, because there is no available
data for estimating the probability of harm.
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A2 Science In Society 3.5
Teacher Notes
3 Explain what you understand by the term risk.
Risk is the chance that something adverse will happen.
To take a risk is deliberately to incur that chance.
Estimating a risk involves defining that something adverse, the hazard, precisely and finding a way of
calculating how often it is likely to happen in particular circumstances. 'Risk' is the chance and the
consequences taken together. In common speech we quite often use the word 'risk' as referring more
to the consequence than to the probability.
4 Suggest three components that have to be considered when estimating any risk.
Three components to be considered in estimating any risk - the probability (eg, whether there is a
'high risk' or not), the event to which probability attaches, and the severity of the consequences. All of
these components are implicit in any discussion of risk.
5 Give an example that you would use to show someone that ‘zero risk’ is an impossibility.
Even if we are at home, we are taking some kinds of risk (eg a house fire or risks associated with
cooking).
6 Give an example to illustrate the difference between a risk you tolerate and a risk you accept.
Examples of risks we tolerate: risk from mobile phone masts, risk of food poisoning from food eaten
in a fast-food outlet.
Examples of risks that we accept: risk of an accident at home (such a burn from boiling water), risks
of riding a bicycle or going for a walk with a dog.
7 Give an example from the supply of energy which shows that some people bear more of the risk
while others benefit.
For instance the building of any dam imposes risk on people nearby whereas the benefits are shared
by people living further away. Similarly, those who live under high-voltage electricity pylons may well
be affected by the cables which benefit lots of people who live well away from the hazard.
8 Give an example of a danger that is particularly dreaded by the public.
People tend to dread low-probability, high-consequence events, such as the terrorist attacks and
nuclear accidents.
9 Order these activities according to the number of cancers and deaths they cause each year in the
UK: having an X-ray, living in a home built on granite, using a mobile phone, living under power lines,
exposure to UV radiation (eg by sunbathing), working in the nuclear industry.
 Skin cancer caused by UV radiation (75 000 cases and 2300 deaths per year)
 Radon in homes (1000 deaths per year from lung cancer)
 Medical uses of X-rays (900 cases of cancer per year)
 Radiation from power lines (conflicting evidence, maybe 3.5 cancer cases per year in Sweden)
 Mobile phones (disputed slight increase in risk of brain cancer, driving and using a mobile phone
may be more dangerous than driving whilst under the influence of alcohol)
 Workers in the nuclear industry (slight increase in risk:
1 to 2% of the cancer deaths may be attributable to radiation exposure)
10 This diagram was used in the report to illustrate the ALARP principle. Risk increases from bottom to
top. Make a larger version of the diagram and add these labels to the diagram to show how it should
be annotated. On the left label the three regions. On the right add the four short notes to the relevant
regions.
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Unacceptable region
Teacher Notes
Risk cannot be justified
except in extraordinary
circumstances
Tolerable only if risk reduction is
impracticable or it its cost is grossly
disproportionate to the improvement gained
The ALARP (or
tolerability) region
Risk tolerable if cost of reduction
would exceed the improvement
gained
Broadly
acceptable region
Necessary to keep checking that
the risk remains at a low level
11 Why is it necessary to have regulatory bodies to control societal risks such as risks from the nuclear
industry?
Regulations impose costs on industry that they might well not undertake voluntarily. Regulators
represent the interests of society against the interests of industry which seeks to minimise costs.
Regulators review evidence and best practice internationally to ensure that the industry takes all
necessary and practicable steps to ensure that it is as safe as practicable.
12 Why are absolute standards for safety not possible? Why do regulators of the nuclear industry have
to exercise judgement on behalf of society?
For severe hazards such as those posed by the nuclear industry, the regulators have to use evidence
and judgement to fix a level of personal exposure that can be regarded as just tolerable, but must not
be exceeded; and they then have to insist that each employer must do better by reducing the
exposure and so the risk to the lowest level that is reasonably practicable. This is again a matter of
judgement taking into account what technology can achieve and what it costs to implement the safety
precautions.
13 (a) How many fatal cancers would arise if every person in a population of 100 000 receives an extra
radiation does of 5 mSv in their lifetime?
5 deaths
(b) The report’s estimate of the average lifetime dose of radiation dose from natural and artificial
sources is 200 mSv. How many people in a population of100 000 dies from cancer caused by
radiation if the risk estimate is correct?
1000 people
(c) The data show that at that time one in four people died from cancer. What proportion of these
deaths was the result of exposure to radiation?
25 000 people from the population of 100 000 die of cancer. 1 in 25 as a result of exposure to
radiation.
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Teacher Notes
(d) By how much do workers in the nuclear industry increase their risk of dying from cancer as a
result of exposure to an extra 100 mSv in their working lives.
Chance of dying from radiation increased by 50% compared to the rest of the population. Chances of
dying from cancer increased from about 25% to about 25.5%.
14 The limits for radiation exposure are kept under review and have been revised since the report was
written. Why do the risk estimates and standards set by the regulators change over time?
The nuclear industry is relatively young. It can take years for the consequences of exposure to low
doses of radiation to be detected because the onset of cancer is delayed. At the time the report was
written the only data for exposed workers were for groups with unusually high exposures, such as
those who worked with radium in the early decades of the 20th century and those who inhaled radon
and its daughters in uranium mining in the middle years of that century.
Since then it has been possible to gather increasing amounts of data from other groups of workers
with lower exposures, such as those in atomic energy installations in the US and the UK. This has
provided more data and allowed the risk estimates to become more precise. This , in turn, has given
regulators the information they need to insist on stricter standards.
15 An industrial plant has a workforce of 250 people who are exposed regularly to the risks from the
manufacturing processes. The rate of deaths in this workforce is 1 in 100 years. Is this tolerable?
In 100 years there is 1 death while a total of 25 000 person- years have been worked.
So the risk of death per person year is 1 in 25 000. This lies within the regions that is generally
regarded as tolerable.
16 In ways would the consequences of a major nuclear accident differ from an accident in an oil refinery
or an aircraft accident? How does this affect the tolerability of the risks?
Many people feel a greater aversion to death from cancer caused by radiation than to death from
other causes. The consequences of a nuclear accident are long term and would continue to affect
people and the environment for many years.
17 Does the risk from nuclear power set a limit to the number of nuclear power stations that should be
built in the UK?
Increasing the number of nuclear plants increases the risk of accident. According to the report, as far
as could be calculated at the time, and taking as much account of the human factor as is practicable
in modern forms of risk calculation, a programme of between 20 and 50 modern nuclear reactors
would have a similar chance of causing death as the installations at Canvey Island, that is some
hundreds of people.
August 2009
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A2 Science In Society 3.5
Student sheets
Introduction
Following the public inquiry which preceded the building a new nuclear power station at Sizewell (see p
145 of your textbook), the chairman recommended to the Health and Safety Executive that it should
publish guidelines on the tolerable levels of individual and social risk to workers and the public from
nuclear power stations. He argued that at the time that there was insufficient public information to allow
understanding of the basis for the regulation of nuclear safety. This activity is based on information in the
document that the HSE published in 1988 and revised in 1992. Much has changed since that time
nevertheless many of the points made in the report still apply today.
In this activity you are going to discuss and answer questions related to ideas and information in the
HSE report. Before you start you should study the information about risk in the boxes on pages 147 and
149 in your textbook.
Experts and the public
The introduction to the report says that, until the chair of the Sizewell Inquiry made his recommendation,
the discussion of the extent of the risks, to people or to the environment from industrial undertakings
tended to be regarded as a matter for experts.
1 Suggest reasons why there was then a view that discussion of risks should be left to experts.
2 Why is it no longer acceptable to ‘leave it to the experts’?
Risk and the tolerability of risk
The report makes a distinction between tolerating a accepting risks. 'Tolerability' does not mean
'acceptability'. It refers to a willingness to live with a risk so as to secure certain benefits and in the
confidence that it is being properly controlled. To tolerate a risk means that we do not regard it as
negligible or something we might ignore, but rather as something we need to keep under review and
reduce still further if and as we can. For a risk to be 'acceptable' on the other hand means that for
purposes of life or work, we are prepared to take it pretty well as it is.
3 Explain what you understand by the term risk.
4 Suggest three components that have to be considered when estimating any risk.
5 Give an example that you would use to show someone that ‘zero risk’ is an impossibility.
6 Give an example to illustrate the difference between a risk you tolerate and a risk you accept.
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A2 Science In Society 3.5
Student sheets
Societal risks
The report concentrates upon certain kinds of risk that are regulated by society
as a whole, with the aim of securing general benefits. When risks are regulated by society, the relevant
judgements cease to be in the hands of the individuals who bear the risk. The risks are shifted around,
so that some people bear more and others less of them; and the benefits may also be unevenly
distributed.
7 Give an example from the supply of energy which shows that some people bear more of the risk
while others benefit.
Societal risk may be redistributed in many other ways : for example through time, so that less risk is
borne now, but more by some future generation. Or one kind of risk may be substituted for another.
People tend to view risk differently according to whether they can judge the hazard directly from
experience, or whether the cause of the danger is not well understood or is particularly dreaded; or
perhaps whether it could result in large adverse consequences from which individuals could not escape.
Thus public expectations about the levels of protection required, or the level of risk which can be
tolerated, may well differ according to the nature of the hazard in question and people's knowledge or
feelings about it.
8 Give an example of a danger that is particularly dreaded by the public.
9 Order these activities according to the number of cancers and deaths they cause each year in the
UK: having an X-ray, living in a home built on granite, using a mobile phone, living under power lines,
exposure to UV radiation (eg by sunbathing), working in the nuclear industry.
The regulation of industrial risk
The report explains that the main tests that are applied in regulating industrial risks are very similar to
those we apply in day to day life. They involve determining:
 whether a given risk is so great or the outcome so unacceptable that it must be refused altogether; or
 whether the risk is, or has been made, so small that no further precaution is necessary; or
 if a risk falls between these two states, that it has been reduced to the lowest level practicable,
bearing in mind the benefits flowing from its acceptance and taking into account the costs of any
further reduction.
Safety law is based on the principle that any risk must be reduced so far as reasonably practicable – in
other words to a level which is 'as low as reasonably practicable' (the ALARP principle). Legally
speaking, this means that unless the expense undertaken is in gross disproportion to the risk, the
employer must undertake the expense. This principle also means that employers are entitled to take into
account how much it is going to cost them to take a safety precaution, and that there is some point
beyond which the regulator should not press them to go; but that they must err on the side of safety.
In applying these principles the regulators issue a large number of standards or codes and a great deal
of guidance stating what is 'reasonably practicable' for a very large number of industrial activities
including the nuclear industry
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©The Nuffield Foundation, 2009
Copies may be made for UK in schools and colleges
A2 Science In Society 3.5
Student sheets
10 This diagram was used in the report to illustrate the ALARP
principle. Risk increases from bottom to top. Make a larger
version of the diagram and add these labels to the diagram to
show how it should be annotated.
On the left label the three regions.
On the right add the four short notes to the relevant regions.



Broadly acceptable region
Unacceptable region
The ALARP (or tolerability) region


Risk cannot be justified except in extraordinary circumstances
Risk tolerable if cost of reduction would exceed the
improvement gained
Tolerable only if risk reduction is impracticable or it its cost is
grossly disproportionate to the improvement gained
Necessary to keep checking that the risk remains at a low level


11 Why is it necessary to have regulatory bodies to control
societal risks such as risks from the nuclear industry?
12 Why are absolute standards for safety not possible? Why do regulators of the nuclear industry have
to exercise judgement on behalf of society?
What level of risk is tolerable?
The report has sections which examine to risks to workers in a nuclear plant during normal operations
and the risk to individuals and society of there being a serious accident.
At the time the report was written the average annual dose to workers in nuclear power stations said to
be about 1 mSv, with a few workers receiving doses greater than 5 mSv in a year.
The report makes the point that there are considerable uncertainties involved in all risk calculations. The
risk of fatal cancer to a person was then estimated to be 5 in
100 000 for every millisievert received uniformly over the whole of a life.
13 (a) How many fatal cancers would arise if every person in a population of
100 000 receives an extra radiation does of 1 mSv in their lifetime?
(b) The report’s estimate of the average lifetime dose of radiation dose from natural and artificial
sources is 200 mSv. How many people in a population of 100 000 dies from cancer caused by
radiation if the risk estimate is correct?
(c) The data shows that at that time one in four people died from cancer. What proportion of these
deaths were the result of exposure to radiation?
(d) By how much do workers in the nuclear industry increase their risk of dying from cancer as a
result of exposure to an extra 100 mSv in their working lives.
14 The limits for radiation exposure are kept under review and have been revised since the report was
written. Why do the risk estimates and standards set by the regulators change over time?
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Student sheets
The report concluded that, the average risk of death for workers in the nuclear industry lay between 1 in
20 000 and 1 in 4000 per year with a risk of 1 in 10 000 or better at power stations. The higher figure
was broadly comparable with the risks borne on average by the workforce in such high risk industries as
metal manufacturing and mineral extraction. The lower figure was of the same order as the average for
all manufacturing industry at the time.
The report suggests that the level of risk borne by the very small number of workers whose dose is near
to the level of 15 mSv was probably about the same as that of many workers in the riskier groups in risky
industries; such as workers in the offshore oil industry, faceworkers in mining, or roofworkers in the
construction industry.
The level of these risks was then difficult to estimate precisely because of gaps in the statistics, but the
authors of the report decided that a risk of death around 1 in 1000 per annum is the most that could
ordinarily be accepted by substantial groups of workers in any industry in the UK, with that level being
exceeded, in practice, only by fishermen and relatively small sub-groups such as helicopter pilots, divers
and demolition workers.
It seemed, to the writers of the report, reasonable to adopt a risk of death of around 1 in 1000 as the
dividing line between what is just about tolerable as a risk to be accepted by any substantial category for
any large part of a working life, and what is unacceptable for any but fairly exceptional groups.
15 An industrial plant has a workforce of 250 people that are exposed regularly to the risks from the
manufacturing processes. The rate of deaths in this workforce is 1 in 100 years. Is this tolerable?
The report concludes by discussing the extent to which the risks to society at large from the nuclear
industry are tolerable. These societal risks include not only the risk of death but also the costs of dealing
with an accident including the consequences of land being unusable because of contamination and the
wider disruption of the lives of communities.
The approach is to compare the risks from the nuclear industry to the risks from other major installations.
The report refers to the oil storage and refinery facilities at Canvey Island where a recent major study of
risk had led to changes intended to cut the risk major accident causing 1500 deaths to be reduced to 1 in
5000 per year.
The report also refers to the Thames Barrier, which was designed, to a standard meant to reduce the
risk of it being overtopped by a freak tide to 1 in 1000 per year. This was, at the time, the estimated
annual risk of an aircraft accident killing 500 or more people in the UK.
16 In ways would the consequences of a major nuclear accident differ from an accident in an oil refinery
or an aircraft accident? How does this affect the tolerability of the risks?
17 Does the risk from nuclear power set a limit to the number of nuclear power stations that should be
built in the UK?
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