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4.2 The Three Safety Factors Important - Coggle Diagram
4.2
The Three Safety Factors
Important
Technical Factors
Technical Factors 1
Plant and Process Design
suitable consideration of safety, at the design stage, will assist in achieving operational safety (it can be hard to use a badly designed plant or process safely).
Designing for safety should be the aim. This implies designing out hazards through hazard elimination
general principles of prevention:
Replacing dangerous activities with those that are not dangerous or less dangerous
(design out hazards)
Avoiding significant risks where hazards remain (wherever possible)
Ensuring significant unavoidable risks are evaluated at the design stage
Combating risks at the source (wherever possible)
Adapting the work to the individual
Adapting to technical progress by designing plant to provide future upgradability
Developing an effective overall accident prevention policy
Designing standard operating procedures (SOPs)
Design Systems for Safety (Basic Principles)
Substitute
for example replace a toxic with a non-toxic material.
Moderate
for instance, redesign processes to avoid high temperatures and pressures, or use flammable gases at concentrations below their lower explosive limit (LEL)
Minimise
for example reduce the amount of hazardous material by reducing batch sizes.
Simplify
avoid complexity of design or operation that increases risk.
Also plants and processes should be designed to fail safe.
Plants and processes should be error resistant and tolerant:
Error resistant systems
prevent human error from happening, for example, aircraft controls designed to prevent a pilot from producing a stall condition.
Error or fault tolerant systemes
are designed to be able to continue to operate in the event of human error or a fault in hardware/software
Avoiding the Domino Effect
Avoiding the domino effect requires design so that failure of one system cannot cause the consequent (and often more severe) failure of others.
Theory of Accident Causes
Active & Passive Safety
Active Safety:
Also called primary safety
consists of systems that are designed to prevent an accident from occurring in the first place.
Passive safety
, also known as secondary safety
consists of systems that are designed to reduce the severity of an accident, should one occur.
Technical Factors 2
Engineering Failures
Engineering failures can occur at any point in the life of a component or engineered system
The Bathtub Curve
shows how the probability of failure changes with age
Region 1
Initial Shake-down period
where errors in design and/or manufacturing lead to early failures
Region 2
the failure rate remains relatively low, is roughly constant, and is dominated by random failures
Bulk of the system's life
Region 3
Components begin to wear out and the overall failure rate gradually increases
Fatigue: an example of engineering failure
Fatigue is failure due to cyclic deformation.
occur gradually over time when the load or stress that a component is subjected to changes in a regular and repetitive manner while it is in service
Fatigue is a kind of cyclic loading
Safety Margins
The more safety critical the application, and/or the more uncertain the operating conditions, the larger the margin that would ideally be used
Strategies in response to fatigue
Fail Safe
Damage tolerance
A component, subsystem or system can be said to be damage tolerant if it safely sustains defects until they can be addressed.
Safe Life
A component is designed to last for its intended service lifetime
Fatigue Resistance
fatigue involves repeated cycling (e.g. from tension to compression and back). A component can be said to be fatigue resistant when it is able to survive a large number of such cycles
There are a few different ways in which to increase a component or structure’s resistance to fatigue:
Low rates of cracks propagation
Increase ‘fracture toughness’,
Difficult crack initiation
Consider a spectrum of different loading conditions, which would include occasional higher than normal tensile loads.
Technical Factor 3
Design, operation, inspection and maintenance
Detecting emerging engineering failures before they happen is essential if accidents are to be avoided.
Non-destructive testing (NDT)
refers to a range of analytical techniques which are used to evaluate the condition of a material, component or system, without destroying it.
Human Factors
Suitably trained and experienced people play a positive role in safety, especially as their problem identification and solving abilities are beyond those of machine
Human Factors Analysis and Classification System (HFACS)
Supervisory factors
Planned inappropriate operations
Failure to correct problem
Inadequate supervision
Supervisory violations
Preconditions for unsafe acts
Environmental factors
Conditions of operators
Personnel factors
Organizational influences
Organizational influences
Organizational process
Human and other resources management
Unsafe acts
Errors (decision errors, skills based errors and perceptual errors)
Violations (routine and exceptional)
Organizational Factors,
local workplace factors and unsafe acts
contribution to accidents
Organizational factors
poor strategic decisions
inadequate organizational processes
(for example, budgeting, planning, communication and auditing)
an
unhealthy organizational culture
(for example, an irresponsible attitude to risk).
Local Workplace Factors
Poor human-machine interface
Insufficient level and quality of supervision
Inadequate equipment / or training
unhealthy local workplace culture (e.g. macho, lackadaisical or bullying).
Time pressure
inadequate staffing levels and/or staff demotivated (e.g. by low status or pay
Unsafe Acts Factors
Unsafe acts are errors and violations of procedures by individuals and teams that occur in the context of local workplace factors, as shaped by organisational factors.
Theory of Accident Causes
The Domino Theory
W.H. Heinrich (1931)
88% of all accidents are caused by unsafe acts of people, 10% by unsafe actions and 2% by “acts of God”
five-factor accident sequence
Unsafe act together with mechanical and physical hazard
Accident
Worker fault
Damage or inquiry
Social environment
Heinrich suggested that removal of one of the factors would prevent the accident and resultant injury
Multiple causation theory
Multiple causation theory is an outgrowth of the domino theory
Accidents contributory factors can be grouped into:
Behavioral
e.g. improper attitude, lack of knowledge, lack of skills and inadequate physical and mental condition.
Environmental
e.g. improper guarding of other hazardous work elements and degradation of equipment through use and unsafe procedures.
The major contribution of this theory is to bring out the fact that rarely, if ever, is an accident the result of a single cause or act.
The pure chance theory
every one of any given set of workers has an equal chance of being involved in an accident
In this theory, all accidents are treated as corresponding to Heinrich’s acts of God
Biased liability theory
Biased liability theory is based on the view that once a worker is involved in an accident, the chances of the same worker becoming involved in future accidents are either increased or decreased as compared to the rest of workers
Accident proneness theory
Accident proneness theory maintains that within a given set of workers, there exists a subset of workers who are more liable to be involved in accidents
The energy transfer theory
This theory is useful for determining injury causation and evaluating energy hazards and control methodology
a worker incurs injury or equipment suffers damage through a change of energy, and that for every change of energy there is a source, a path and a receiver.