IA5 Flashcards
An organization should carry out a risk assessment before developing a safe system of work.
(a) Outline the factors that should be considered when carrying out a risk assessment.
The factors to be considered when carrying out a risk
assessment include:
the detail of the activity or task concerned and the
equipment and materials involved
any guidelines or information provided by the
manufacturer
the number and type of persons to be involved in the
activity
the hazards associated with the activity and the likelihood
and severity of their associated risks
the adequacy of existing control measures
accident history and previous experience
legal requirements
the need to involve and consult workers and to use
appropriate and familiar language to enhance
understanding
monitoring the effects of the assessment once it has been
introduced and arranging for periodic reviews
ensuring the competency of the assessor.
(a) Outline the principles, application, and limitations of
Event Tree Analysis as a risk assessment
technique.
(b) A mainframe computer suite has a protective
system to limit the effects of fire. The system
comprises a smoke detector connected by a power
supply to a mechanism for releasing extinguishing
gas. It has been estimated that a fire will occur once
every 5 years (f=0.2/year). Reliability data for the
system components are as follows:
Component
Reliability
Detector
0.90
Power supply
0.99
Extinguishing gas mechanism
0.95
(i) Construct an event tree for the above scenario to
calculate the frequency of an uncontrolled fire in the
computer suite.
(ii) Suggest ways in which the reliability of the system
could be improved.
(a) Event Tree Analysis is based upon binary logic
for example, whether an event happens or does not or
whether a component succeeds or fails.
It is often used to estimate the likelihood of success
or failure of safety systems or to assess particular
outcomes from an undesired event.
It starts with the initiating event and ends with the
probability of a situation being controlled or not. It is
limited by the lack of knowledge of component
reliability and other data and since it considers only
two possibilities success or failure it does not
take into account partial downgrade (i e limited
success).
(b)(i) Event tree: - (Sorry you have to construct and event tree on paper cos I can’t upload it)
(b)(ii)The reliability of the system could have been improved by:
choosing more reliable components
using components in parallel, for example since the detector was the least reliable component increasing its number
installing a second independent but parallel system.
A chemical reaction vessel is partially filled with a mixture of highly flammable liquids.
It is possible that the vessel headspace may contain a concentration of vapor which, in the presence of sufficient oxygen, is capable of being ignited. A powder is then automatically fed into this vessel.
Adding the powder may sometimes cause an electrostatic spark to occur
with enough energy to ignite any flammable vapor. There is concern that there may be an ignition
during the addition of the powder.
To reduce the risk of ignition, an inert gas blanket system is used within the vessel headspace designed to keep oxygen below levels required to support combustion. In addition, a sensor system is used to monitor vessel oxygen levels. Either system may fail. If the inert gas blanketing system and the oxygen sensor fail simultaneously, oxygen levels can be high enough to support combustion. The probability and frequency data for this system are given below.
Failure type / event
Probability
Vessel headspace contains a concentration of vapor capable of being
ignited
0.5
Addition of powder produces spark with enough energy to ignite vapor
0.8
Inert gas blanketing system fails
0.2 per year
Oxygen system sensor fails
0.1
(a)Draw a simple fault tree AND , using the above data, calculate the frequency of an ignition.
(b)Describe, with justification, TWO plant OR process modifications that you would recommend to reduce the risk of an ignition in the vessel
headspace.
(a) A fault tree (Sorry you have to construct and fault tree on paper cos I can’t upload it)
The fault tree should have enabled the
calculation of frequency of ignition would be
0.008 per year, or once in every 125 years
(b) A description of any relevant modifications
would be appropriate, provided those which
would make a greater contribution to
reducing the overall risk was selected.
These could have included:
replacing the powder feed with a slurry
in a conducting liquid selecting and using materials with higher flashpoints to minimize the probability of a flammable atmosphere redesigning the nitrogen blanketing system to improve reliability.
(a) Explain the purpose of Job Safety
Analysis.
(b) Outline the methodology of Job Safety Analysis.
(a) The purpose of Job Safety Analysis is to assess the hazards and risks associated with each component of a specific task,
to establish whether adequate precautions are in place in order
to reduce the risk of injury, and to produce a system of work
that provides a safe way of performing the task.
(b)
The methodology of Job Safety Analysis involves:
ü
selecting the job or work to be examined
ü
breaking g it down into its chronological component parts
ü
examining each part to identify its hazards and
associated risks
ü
developing control measures to eliminate or mitigate the
risks installing the control measures as a safe system of
work
ü
ensuring that the system is well understood by both
management and workers.
Additionally, it will be necessary to review both the job and its
a safe system of work at regular intervals in order to introduce
amendments when conditions and or circumstances have changed.
A manufacturing company with major on and off site hazards is analysing the
risks and contr ols associated with a particular process and containment failure.
Following a process containment failure (f=0.5/yr), a failure detection mechanism
s hould detect the release. Once detected, an alarm sounds then a suppressant is
activated. Finally, in order to control the initial release, an operator is required to
initiate manual control measures following the release of the suppressant.
As part of the analysis, the company has decided to quantify the risks
associated
with a substance release from the proce ss and develop a quantified event tree
from the data.
Activity
Frequency/reliability
Process containment failure
0.5 per year
Failure detection
0.95
Alarm sounders
0.99
Release suppression
0.85
Manual control measures activated
0.8
(a)
Using
the data provided, draw an event tree that shows the
sequence of events following a process containment failure.
6
marks
(b)
Calculate
the frequency of an uncontrolled release resulting from
process containment failure.
6
marks
(c)
Outline
the factors that that should be considered when determining
whether the frequency of the uncontrolled risk is tolerable or not.
5
marks
(d)
If the risk is found to be intolerable,
outline the methodology for a
cost-benefit analysis with respect to the process described.
(a)
An event tree sim
ilar to the one on the next page should have
been constructed.
(b)
Calculation on following page.
(c)
Factors to be considered in determining whether the
frequency of the
ü
uncontrolled risk is tolerable or not include:
ü
the plant location taking into acc ount the health and
environmental implications of a release
ü
the cause of the release such as for example, as a
result of a catastrophe together with the inevitable
public outrage that it would arouse
ü
historical data
ü
relevant legal requirements
ü
the impact t hat a failure would have on production and
the cost of control measures
ü
published risk data such as those contained in
Reducing Risks Protecting People.
(d)
The first step of the methodology for a cost benefit analysis
would comprise the quantification of process losses and
improvement costs in terms of monetary value. Should a
comparison indicate that process losses together with other
possible losses such as damage to the organisation’s
reputation exceed improvement costs, the improvement
work should be carried out. A payback period would need to
be established with due consideration being given to the
value of the money involved spread over the period of time.
a Event
tree:
(b)
The frequency of an uncontrolled release resulting from process containment failure can be calculate
d
as:
Release 1 = 0.5 x 0.05 = 0.025/yr
Release 2 = 0.5 x 0.95 x 0.01 = 0.00475/yr
Release 3 = 0.5 x 0.95 x 0.99 x 0.15 = 0.071/yr
Release 4 = 0.5 x 0.95 x 0.99 x 0.85 x 0.2 = 0.08/yr
The frequency of an uncontrolled release would therefore be:
0.025 + 0.0
0475 + 0.071 + 0.08 = 0.181/yr or once every 5.5 years.
(a) Outline the use and limitations of fault tr ee analysis. 4 marks (b) A machine operator is required to reach between the tools of a vertical hydraulic press between each cycle of the press. Under fault conditions, the operator is at risk from a crushing injury due to either (a) the press tool falling by gravity or (b) an unplanned (powered) stroke of the press. The expected frequencies of the failures that would lead to either of these effects are given in the table below: Failure type Frequency (per year) Effect Flexible hose failure 0.2 a Detach ment of press tool 0.1 a Hydraulic valve failure 0.05 a Activation button failure 0.05 b Electrical fault 0.1 b (i) Given that the operator is at risk for 20 per cent of the time that the machine is operating, construct and quantify a simple fault tr ee to show the expected frequency of the top event (a crushing injury to the operator’s hand). 10 marks (ii) Outline , with reasons, whether or not the level of risk calculated should be tolerated. 4 marks (iii) Assuming that the nature of the task cannot be changed, explain how the fault tree might be used to prioritise remedial actions.
(a)
Fault tree analysis is useful in analysing accidents,
where there are multiple causes to an accident, to
calculate the probability of the top event. It ca n also be
used to identify the most effective points of intervention
in order to reduce the probability of the top event
occurring.
Fault tree analysis is limited by the requirement of
skilled analysts to work the calculations out in complex
situations, an d its reliance on the accuracy and
availability of failure data.
(b)
(i)
A fault tree similar to the one on the next page
should have been constructed and quantified.
(ii)
The risk of 1 accident (per press) in 10 years
(calculated from the fault is too high. If, for
example, there are 10 presses in the factory, there
is the risk of one serious accident per year, which
should not be tolerated.
(iii)
The general principle of using probability data in a
fault tree so that priority is given to those actions
that would give the greatest reduction in the
probability of the undesired events. For example:
gravity fall was highlighted as the most likely
event, so priority should have been given to
actions to prevent this.
An organisation wants to build a new gas compression installation to provide energy for its manufacturing processes. An explosion in the installation could affect the public and a nearby railway line. In view of this, the organisation has been told that a qualitative risk assessment for the new installation may not be adequate and that some aspects of the risk require a quantitative risk assessment. (a) Explain the terms: i) Qualitative risk assessment 3 marks ii) Quantitative risk assessment 2 marks (b) Identify external sources of information and advice that the organisation could refer to when deciding whether the risk from the new installation is acceptable. 5 marks (c) A preliminary part of the risk assessme nt process is to be a hazard and operability (HAZOP) study. Describe the principles and methodology of a HAZOP study.
(a) i) Qualitative risk assessments are subjective descriptio ns. Broad categories are used to classify likelihood and consequences. ii) Quantitative risk assessments use numerical data. Actual numerical data is used to represent probability and consequences. (b) External sources of information to be identified in clude: ü enforcing agencies ü competent consultants ü similar organisations ü insurance ü codes of practice ü guidance. (c) HAZard and OPerability Studies (HAZOPS) is a tool widely used in high risk sectors for process design and safety assessments. The principles and methodology to be discussed include: ü the intention of the HAZOPS ü a team approach ü the nature of the activity ü the use of guide words ü how the guide words are applied to the parameters of design and intent. Key terms to use in your descriptions include de viations, design intent, and guide words.
For a range of internal information sources: (a) outline how EACH source contributes to risk assessment 7 marks (b) outline the limitations of these information s ources.
(a)
Internal information can help in the identification of hazardous
events. Sources include:
ü
analysis of accidents and injuries to identify types of
accident that occur and the type of injuries that result
ü
analysis of personal c haracteristics these may affect
the likelihood and severity of injury
ü
analysis by time and space there may be site specific
concerns, or particular shifts may give rise to concerns
ü
ill health data may help to show the effects of work
activities
ü
maint enance records identify machinery damage and
damage to building fabric, can indicate the likelihood of
personal injury.
(b)
The data may be out of date or incomplete. ill
health data may
be difficult to obtain due to the timescales between exposure
and illness, workers move on and non occupational variables
can impact on individual health.
