Research
Brief
Managing the risk associated with sudden incapacity in
safety critical occupations
T663 - September 2009
Background
In order to protect the public and employees on
the railways, the industry has developed systems
to limit risk from the sudden incapacity of an
employee carrying out a safety critical task. For
example the Railway Group Standard GO/
RT3451 contains a general health requirement
which states that:
'Infrastructure managers and railway
undertakings shall not permit persons to carry
out train dispatch, shunting or train driving
work where there is reason to believe that a
person is suffering from medical conditions or
be taking any medication, drugs or
substances, which are likely to cause:
a) Sudden loss of consciousness
b) Impairment of awareness or concentration
c) Sudden incapacity
widespread concerns have been raised over a
lack of consistency in interpretation of the phrase
'likely to cause'. These concerns have been
discussed at meetings of the Association of
Railway Industry Occupational Health Providers
(ARIOPS), its sub-committee the Rail Medical
Advisory Group (RMAG), during the course of
the research and at the recent Occupational
Health Seminar organised by RSSB.
Aims
There is a need to provide occupational health
physicians (OHPs) with an objective
interpretation of the phrase 'likely to cause'. The
overall aim of this research, using established
risk assessment techniques, was to identify the
frequencies of sudden incapacity or impairment
while performing safety critical tasks which are
acceptable to the rail industry. Two publications
have been produced - a research report, and a
guidance document.
d) Impairment of balance or co-ordination
e) Significant limitation of mobility.'
However, the phrase 'likely to cause' has not
been defined, and renders the standard
completely dependent on the subjective opinion
of examining physicians and the responsible duty
holder. The scope of this research was about the
circumstances in which the duty holder seeks the
advice of a physician. In the absence of guidance
from the rail industry on acceptable risk
generally, the physicians will be inclined to limit
the activities of employees to minimise the risk
from medical incapacitation. Although an
individual who fails to meet the fitness standard
may be permitted to continue working, provided
a risk assessment has been carried out,
RSSB
Block 2 Angel Square,
1 Torrens Street
London
EC1V 1NY
Method
The research involved:
Data gathering. A comprehensive review of the
approach to managing the risk of sudden
incapacity in other safety critical industries, and
in the rail industry in other countries.
Polling the industry on their views on
accident risk due to medical factors and
their current decision making processes
regarding this. A questionnaire was used to
seek the industry's views on accident risk due to
medical factors and current decision making
processes. Stakeholders were asked to describe
the risk assessment and decision making
Research and Development Programme
www.rssb.co.uk/research/
rail_industry_research_programme.asp
research@rssb.co.uk
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Managing the risk associated with sudden incapacity in
safety critical occupations
T663 - September 2009
processes surrounding failure or restricted pass
of an RGS medical assessment.
Stakeholder engagement. In addition to the
questionnaire, the industry was consulted, via a
stakeholder workshop, to provide input into the
risk model. Also, letters were sent to
manufacturers of railway engineering controls to
ascertain the reliability of their systems.
Producing a series of values for acceptable
frequency of impairment while performing
different safety critical tasks. An established
risk assessment technique was used to estimate
the current frequency and consequences of (and
hence risk from) incidents which could have been
caused by sudden incapacity. From these
estimates and the data gathered during the
stakeholder engagement process, the
acceptable frequencies of impairment were
developed.
Developing guidance for OHPs and duty
holders. Guidance was produced, with worked
examples for a sample of safety critical tasks, to
enable both OHPs and duty holders to use the
information on the associated frequencies of
impairment likely to be acceptable to industry.
The term unavoidable impairment has been
included in the guidance document in preference
to sudden incapacity to encompass any condition
or symptom categorised by situations a) to e) in
the general health requirements.
Findings
The research found that general health
requirements in Australia and Canada are similar
to those mandated in Great Britain. This covered
medical assessment frequencies, the medical
conditions considered, and how medical
assessment results are classified. Other safety
critical industries such as aviation, road
transport, maritime, and fire services all have
medical fitness requirements, which are broadly
similar to those of the GB rail industry. The
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research details the risk assessment procedures
and medical conditions assessed by each
industry.
From the rail industry poll there appears to be a
split between companies with specific risk
assessment procedures or capability
assessments in place to deal with occupational
health issues, and companies who rely solely on
the OHP's recommendations to make the fitness
for work decisions. Whilst all respondents gave
details on their risk assessment and decisionmaking processes, no company provided any
specific cut-off points or criteria. Some
respondents highlighted issues associated with
cooperation between OHPs and duty holders.
This included: a lack of familiarity of some OHPs
with the railway environment; a lack of clarity
around the criteria to which the OHPs work;
logistical issues when trying to meet to discuss
difficult cases. 27 industry organisations were
involved in the research in one way or another.
The information gathered during the project
suggested that the safety risk associated with
unavoidable impairment is relatively low, due to:
the low frequency of recorded events; the
existing organisational and engineering controls;
and the current medical assessment process.
The risk assessment undertaken as part of the
research supported these findings.
As the acceptable frequency of unavoidable
impairment was developed, there were a number
of parameters which had a significant effect on
the acceptable frequency. The key parameters
were:
Whether the task would typically involve
lone or group working
 The engineering controls in place to
mitigate an unavoidable impairment event
 Organisational controls to prevent
unavoidable impairment whilst carrying out
the safety critical task

Indeed, when the existing organisational and
engineering controls are taken into account for
calculating the acceptable frequency of
unavoidable impairment for certain safety critical
groups, a relatively high cut-off frequency is
derived. For example, the acceptable frequency
of unavoidable impairment for individual train
drivers is estimated as 0.43 events/person/year,
this equates to approximately 1 unavoidable
impairment event every 2.5 years. This
compares with a frequency of 0.02 events/
person/year set by the DVLA for vocational road
vehicle drivers, which is often taken into account
by rail OHPs when assessing train drivers. Such
a comparison suggests there may be room for
flexibility in interpreting the medical findings
against the requirements of the Railway Group
Standard. On the other hand, for some safety
critical groups the research has determined that
a low frequency of unavoidable impairment is
acceptable; thus, there is limited flexibility in
interpretation of medical findings. For example,
an electrical control officer has an acceptable
frequency of unavoidable impairment of only
0.02 events/person/year; this equates to
approximately 1 unavoidable impairment event
every 50 years (the same as the DVLA
standard).
When compared with the allowable frequency for
the aviation industry (which has 0.01 events/
person/year) and the road transport industry (the
DVLA standard), this might suggest that the rail
industry could adopt less stringent medical
standards. However, it would be difficult to make
this comparison because many of the relevant
tasks and associated parameters are very
different.
Guidance has been developed which presents
worked examples of how acceptable frequencies
of unavoidable impairment were derived for
selected safety critical tasks. The document can
be used by OHPs to explain to duty holders how
an evidence-based medical fitness for work
decision was made.
Should the industry accept the findings of this
research project it may be appropriate for the
likely to cause statement within the general
health clause to be replaced with a more specific
phrase detailing the values presented in the
guidance?
Next steps
Duty holders should consider the adoption
of the guidance for their own activities.
 In the light of their experience with this
guidance, further consideration should be
given to the codifying of this guidance
within the relevant standards including
consideration of whether it may be
appropriate for the likely to cause
statement within the general health clause
to be replaced with more specific detailing
of the values presented in the guidance.

Other observations arising from the research,
which are not being taken forward (RSSB does
not have stakeholder endorsed plans or
resources to undertake this at the present time)
include the following:
A number of stakeholders said that there
was a need for an occupational health
model similar to the Safety Risk Model.
There could be an assessment of the
current methods and existing KPIs used to
capture medical related incidents / near
misses, unavoidable impairment events, to
support improved future data collection.
 There was potential to agree a list of
medical conditions, possibly akin to the
DVLA, CAA, Australian, and Canadian rail
guidance.
 The Safety Risk Model could be expanded
to prepare acceptable frequency values for
other safety critical tasks.

RSSB will be routinely following up progress in
this area.
RSSB
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Managing the risk associated with sudden incapacity in
safety critical occupations
T663 - September 2009
Benefits
The principal benefits of undertaking this
research will be realised if health providers start
to use the recommended quantitative values in
assessing whether a staff member in a safety
critical role is safe to resume normal duties,
rather than defaulting to the current cautious
approach. It will not be possible to measure the
improvement as there are no industry-wide
metrics available on which to base a 'before' and
'after' analysis although individual duty holders
should start to see positive results once they and
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their OHPs decide whether to adopt the
guidelines which have been produced as part of
this research.
Contact
Michael Woods
Head of Operations Research
R&D Programme
RSSB
research@rssb.co.uk