3. Single Cause Domino Theory
Heinrich’s theory
Each factor is the fault of the factor that immediately
precedes it
A preventable injury is the natural culmination of a
series of events or circumstances, which occur in a
fixed logical order
4. Single Cause Domino Theory
Ancestry & Social
Environment
Fault of Person Unsafe Act or
Condition
Accident Injury
5. Single Cause Domino Theory
If one of the dominoes is removed then the chain
of events will be halted, and the accident will not
happen
Element 3 (unsafe act and/or mechanical or
physical hazard) is probably the easiest factor to
remove
6. Single Cause Domino Theory
Bird & Loftus extended Heinrich’s theory to encompass the influence of
management in the cause & effect of accidents
They suggested a modified sequence as follows:
Lack of management control, permitting
Basic causes (personal & job factors), leading to
Immediate causes (substandard practices or conditions), which are the direct cause of
The accident, which results in
Loss (negligible, minor, serious or catastrophic
This modified sequence can be applied to every accident and is of basic
importance to loss control management
7. Multiple Causation
May be more than one cause, not only in sequence, but
occurring at the same time
In accident investigation all causes must be identified
Usually simple accidents have a single cause
Major disasters normally have multiple causes
9. Unsafe Acts
Categories:
Operating without clearance
Operating at unsafe speed
Rendering safety devices inoperative
Using unsafe equipment, or using it unsafely
Unsafe methods e.g. loading, carrying, mixing
Adopting unsafe position or posture
Working on moving or dangerous equipment
Horseplay e.g. distracting, teasing, startling
Failure to wear PPE
Lack of concentration; fatigue or ill health
Human Factors
10. Unsafe Acts
Unsafe acts can be active or passive:
Active Unsafe Acts:
Worker deliberately removes machine guard
Passive Unsafe Acts:
More difficult to deal with
By pursuing an active safety policy, it is possible to achieve a
reduction in bad habit s and hence accidents
12. Unsafe Acts/Conditions
The picture shows how unsafe acts & conditions may interact to produce an accident. Accident
potential is increased when unsafe acts & conditions occur simultaneously. Of course, this is
not to say that an act or condition alone could not result in an accident.
Unsafe Acts Unsafe
Conditions
Accident
Potential
13. Accident Reporting
Information should be kept for all injuries, and
preferably for near misses
The safety practitioner needs to design a
suitable form to ensure that he gets the
information that he needs for investigations
14. Accident Investigation Records
Format:
Name & personal details of victim
Date, day and time of accident
Location of accident
Occupation of victim
Job being done at time
Nature of injury or damage
What inflicted the injury or damage
Who had control of the cause of the injury or damage
What actually happened
Basic and immediate causes
Immediate remedial action taken
Recommendations to prevent recurrence
15. Use of Investigation Records
Accident records are useless if they are used only to count accidents. Detailed and
thorough study of the records as part of the normal ongoing accident prevention
programme should yield the following useful information:
Relative importance of the various injury & damage sources
Conditions, processes, machines and activities which cause the injuries/damage
The extent of repetition of each type of injury or accident in each operation
Accident repeaters, I.e. those workers who tend to be repeatedly injured or are involved
in more accidents
How to prevent similar accidents in future
16. Accident Investigation
Could be carried out by:
Safety Practitioner
Management or Supervisor
Safety Representative
Inspector
A joint investigation by company/safety rep is often a good idea
An investigation which does not discover what went wrong, and produce
some useful information and recommendations for corrective action, is just a
waste of time
17. Accident Investigation
Initial Actions
Questioning the victim
Treatment of victim is first priority
Immediate questioning may not be possible - they should be allowed to collect their
thoughts and control their nerves
Witnesses & Conditions
Investigator can usually go to accident scene and get a fairly complete story from
on-site conditions and witnesses
In all serious accidents and in all other cases where practicable, conditions at
accident scene should remain undisturbed until investigation is complete
18. Investigators
Immediate supervisor:
Likely to know most about the situation
Knows his own people better than anyone
Has personal interest in determining causes, as accidents
affect the efficiency and morale of his department
Familiarity with staff could cause problems
19. Investigators
Recognising Hazards
Familiarity with plant, equipment and layout of operations will assist in
recognising hazards that have been overlooked for some time
Unsafe acts, as well as conditions, contribute towards most accidents
It is not sufficient merely to recommend fitting a guard while overlooking the
unsafe act, such as rendering the guard ineffective or placing hands in the
danger zone
It is also insufficient to limit attention to an unsafe act if fitting a better guard
would reduce the likelihood of injury
20. Investigators
Safety Practitioner
Necessary in more serious cases
Supervisor may not have necessary authority
Should seek assistance from local supervisor
Investigator must have authority to go as far as is
necessary to get to the cause of the problem
21. The Investigation
Promptness
As soon as possible after the event
Facts will be easier to determine and more details will be
remembered by those involved
Fire
Helpful if investigator is present during the fire
Investigator may gain useful information by watching the
activities of firemen
22. The Investigation
Evidence
Depending on severity of any injuries or damage, investigator
should be present during clear-up and reinstatement as
valuable clues may otherwise be missed
Failing which, supervisor should take it upon himself to collect
the necessary evidence
23. The Investigation
Equipment
Photographic equipment
Portable lights (electricity may be switched off or accident scene may be poorly lit)
Sketchpad, pencils and measuring equipment
Record-keeping equipment e.g. notebook and cassette recorder
Sample collection equipment e.g. jars, paper bags, cartons etc.
Tools for cleaning debris or spillages should also be available
Portable gas/vapour detecting equipment
24. Accident Investigation Procedure
1. Inspection of the accident scene to collect any information relating to
physical conditions of the plant, equipment and building
2. Interview witnesses and others likely to give information concerning any
unsafe acts or conditions which may have contributed to the accident
3. Summarise all available evidence accurately in a written report to
management, recommending future actions to prevent a recurrence
25. Inspection of the Scene
Careful, detailed look at accident scene, evaluating and noting the following:
Extent & severity of damage
Damage to surrounding property
Environmental conditions which may have had some bearing
on the accident, such as temperature, ventilation, humidity and
illumination
Survey the accident scene to see if there are any obvious dangerous physical
conditions which may have been responsible for the accident
26. Inspection of the Scene
In the case of spillages, splashes or other escapes of poisonous, explosive,
flammable or other dangerous material, it may be necessary to take samples
for subsequent investigation
Where machinery or other equipment has been involved, it may be necessary
to issue instructions prohibiting the use or repair of it until the investigation
has been completed
27. Talking with On-Site Personnel
Easy to upset people when asking questions about what has been done, or
what has not been done
Casual remarks made during the site inspection may be quite revealing and
the investigator should continue to talk to any personnel involved near the
scene of the accident
This would also serve as an ideal opportunity to explain the object of the
exercise is to discover and root out the causes so as to prevent a repetition. It
is not to apportion blame or to criticise any individual
28. Interviewing Witnesses
Types of Witness
Primary witness
The victim
Secondary witness
Extremely rare, the eyewitness
How many people really see the instant of an accident?
Tertiary witness
Can offer variety of corroborative statements regarding the acts of people or
environmental
29. Interviewing Witnesses
Putting witnesses at ease
Explain fully purpose of investigation
Encourage participation and involvement
Show interest in any ideas they might have about possible
preventive measures
Witness must be assured that the purpose of the investigation
is not to blame anyone, but to attempt to find out the cause and
thereby reduce possibility of a recurrence
30. Interviewing Witnesses
Interview Location
Best to carry out interviews at scene of accident, as it is
easier for those involved to communicate effectively with
“props” close to hand
Easier to explain what happened if witnesses are able to
point out specific things and recall their actions related to
specific locations
31. Interviewing Witnesses
Question Phrasing
Open ended question - what, where, when, how or who
Questions starting with why may put witness on the defensive
Typical questions:
What happened? What did you see?What time was it?
Where were you at the time? Where was the victim?
When did you realise something was wrong?
How did it happen? How were you involved?
How could it have been prevented?
Who else was involved? Who else saw it? Who reported it?
32. Interviewing Witnesses
Attitude
“What happened” will often promote the fullest response and it is vital the investigator
listens, without interruption, to the witness’s account of the accident
If something is not understood, investigator should wait until witness has completed his
account before asking for clarification
Do not disagree with any of witness’s statement or make any judgements on his
evidence alone
What a witness believes to have happened will depend to some extent on just how he
perceived the situation, even though this might conflict with the actual facts
33. Interviewing Witnesses
Conclusion
When witness’s account of accident has been heard,
investigator should repeat it to witness to ensure account is fully
understood
Interview should be concluded on a positive note, which is best
achieved by discussing any ideas he may have regarding
prevention of a similar occurrence - this will serve to reaffirm
the purpose of the interview and ensure the witness’s further
co-operation, should it be needed
34. Interviewing the Victim
Ideally first to be interviewed
Injuries may be serious, or may be suffering
from shock
Should be interviewed at the earliest opportunity
General principles for interviewing witnesses
apply
35. What Should be Investigated
ALL incidents/accidents should be investigated
Purpose is to find the cause, with the intention of
preventing a recurrence, rather than
apportioning blame
An injury usually involves some degree of blame
falling on management, supervision, victim or
workers