A system dynamics simulation model of occupational safety has
been developed. It is built using the idea that a number of systems
archetypes are at work in occupational safety (Moizer, 1994).
From a simple causal diagram, a generic simulation model has been
developed and subsequently validated using data from a medium-large
manufacturing site in central Scotland (Moizer, 1996).
Ithink 3.0 was the system dynamics package used to build the quantitative
model. The simulation model has been validated with company data
stretching back in monthly time steps over a three year period.
There was a close match between the model outputs and historical
data. This was backed up by a number of structural, behavioural
and policy tests suggested by Forrester and Senge (1980) and Sterman
(1983). Several different verification tests confirmed that the
model was representative of the safety system which emerged, both
behaviourally and often on a point-by-point basis. The validated
model met with the managers approval. They were satisfied that
the model replicated the behaviour of their own occupational safety
system. The simulation was set up to run from the present to three
years into the future. The purpose of the study was to capture
the managers opinions on the potential of the model in assisting
their company and the wider business world in dealing with occupational
The managers were neither involved in the collation of data or
its analysis, nor in initialising the model. The finished product
could be regarded by the company as a 'black box' model.
Three managers were presented by the model builder with an overview
of system thinking and were taken in summary form through the
model's conception, construction and operation. The interface
shown in figure 1 was revealed to them. The managers were then
asked to become players and experiment with the safety game simulation.
They were able to follow through the instructions, and quickly
involved themselves in model experimentation. As you can see from
the interface shown in figure 1, none of the construction layer
of the model was visible to the players. The slide bars represented
policies. The players were given the opportunity to make policy
decisions simply by dragging these bars back and forth to either
switch them on or off, or heightening or lessening their effect.
The three players experimented or 'flew' the simulation. They
were then asked to discuss the suitability of the model as a learning
or policy tool.
A facilitated group discussion was conducted with the three managers.
They each held very different positions within the company. The
first, and most dominant interviewee was the plant safety professional.
He was a graduate engineer with twenty years engineering and safety
experience, and was very adept at building large databases and
spreadsheet models. The second was a long-serving senior line
manager, having worked for thirty years at the same plant. The
last was a young management trainee who was a graduate engineer
and had been with the company for one week. This mix allowed the
interviewer to obtain the respective opinions of a group consisting
of people from different backgrounds.
The qualitative method applied to gain an understanding of the
processes used to evaluate the simulation model's potential role
allowed a reasonably unbiased picture of the groups opinion to
Initial Responses to the Simulation Model
The discussion opened up with the general question;
"Is the occupational safety model, a learning
or policy tool ?" [Interviewer]
This was followed up by the more direct question;
"How might the simulation model assist your
company ?" [Interviewer]
The initial responses were lengthy and encouraging;
"Well I think it could be used by managers or anyone involved in the field of safety to learn about causes and effects, and what can happen if we change anything in particular, how that might affect the overall picture . . .
It would be used to try and explore what the most effective measures would be . . .
We would follow the path that the model suggested was the best path and monitor the effect to see if the two were in agreement . . .
If successful then we could use it [the model] to
look at the future so that we could set policies so we weren't
stabbing in the dark, but initially very much a learning tool
and probably less of a policy making tool." [Safety Professional]
"I think this can certainly be as in this company . . . a way they can see what it [safety] is going to cost . . .
It would certainly highlight that it [following the
model's policies] would save a lot of injuries, but at the same
time can save money and that makes good management sense."
"I've got a degree of scepticism, especially
when looking or basing future policies on those sort of results.
I wonder how it would differ from department to department, where
we consider accidents do occur frequently that are basically unavoidable
. . . it looked good, but that would be my one worry." [Management
Here three different views of the model unfold. The safety professional
appeared to have a good layman's understanding of how the model
worked, and what its potential and limitations were. He saw the
model as suitable for teaching people about the effects of different
policies as a first staging post, and the potential to use it
to assist with strategic decisions, although most of his comments
suggested using the model as a strategic evaluation tool.
The line manager immediately saw the model in a demonstrational
capacity, describing how you could show people the effects of
safety upon accidents and their requisite costs. This appeared
to be a double-edged response, acknowledging the use of the model
to stress accident reduction and cost minimisation.
Lastly, the trainee, being new to the company and occupational
safety could obviously make a lesser contribution to the debate.
His comments may suggest that he had a lower understanding of
the holistic nature of the model, and was querying specific operational
detail. He may not have appreciated the reason for aggregating
data, i.e. to obtain a manageable overview of the principal variables
in this complex safety system.
The purpose of the model was then re-iterated to the group. That
being to capture an understanding of the emergent behaviour of
the system, rather than examining the numerical outputs on a point-by-point
Discussion of the Principal Model Policy
The group had discovered from experimenting with the model that
from the policies at hand, training appeared to exert the most
leverage over both accidents and safety costs. This allowed the
policy to be given the lions share of verbal evaluation.
The model had stimulated the group to debate about the role of
training and its effectiveness, and they were able to debate this
issue at length. A discussion about the various training approaches
ensued. This allowed the group to query the validity of the model.
Questions were raised as to why all the training mediums had been
aggregated into one policy;
"You could decide to spend double the amount
of time on training . . . the model doesn't know how effective
that training is. Inappropriate training you would expect it to
have a minor effect, whereas, better targeted training would obviously
be more effective. Now it's probably too much for a model to be
able to pick up." [Safety Professional]
"If we've got a lot of duff [poor] training
courses, then really were only ourselves to blame." [Production
It was again pointed out to the group that the model was not an
operational one, rather it worked at the strategic level, examining
wide policy areas;
"You could have broad bands of training, you've got training where you go away on a course off site, or if it's on site you're isolated from your work environment . . .
That would be external training . . .
Off-the-job training is a defined course that covers
topics, and you go back to your job and it might not change the
way you work. On-the-job training should, because you're doing
it on-the-job, change the way you work, and in many cases the
effects could be significantly different." [Safety Professional]
A debate had opened up about the validity of the model. This concerned
the aggregation of internal and external training. An understanding
developed of the impact of different training approaches upon
safety behaviour. The group made it clear that to disagregate
the types of training could more accurately reflect real policy.
This debate could be regarded as very pertinent to the argument
that the model was focused at policy making, because the discussion
had gone beyond the emergent system behaviour and onto the actual
structure of the model and how it should best have been initialised.
The group was trying to find a way to most effectively evaluate
their training policy using the model of their work environment.
Building a satisfactory structure to fit their firm took precedence
here over learning about the general effects of training.
The Effect of the Interface on the Model's Application
The group were again asked for their opinions on the model's effectiveness
in enhancing learning and policy-making. The actual interface
was brought into the discussion, and its user friendliness was
brought to their attention. They were then queried about the interface's
importance within learning or policy-making situations;
"The problems you would face there are the scepticism. If they're [users] not familiar with computers or they don't understand modelling . . .
They have to be comfortable with the process and understand what it is setting out to achieve . . . the model has been developed to the stage that you can use sliders and check graphs. Depending on the audience you're trying to reach that will only reach a certain proportion of them . . .
Ideally you want something which will work in an interactive way which that [the model] does . . .
With someone at a lower level of management or supervisory
level, you could play with that and it might be instead of a chart
it would show a pile of dead bodies. So that they could visually,
not just on a graph get an appreciation . . . so taking that [the
model] a stage further . . .follow the same as a flight simulator
and keep developing that, if the aim is to develop a package that
can be used for training." [Safety Professional]
The group were asked about the interface for the model acting
as a policy tool to assist with resource allocation;
"It doesn't need to be pretty to do that, just
understandable." [Safety Professional]
The group were able to differentiate between the needs of the
user interface for learning, where it was made clear that the
outputs needed to be more visual than graphs, and the low priority
of aesthetics to the planner. Useful suggestions were made as
to how to improve the learning experience, for example, the dead
bodies piling up instead of a graph unfolding. The slide bars
and table functions close at hand were appreciated. This suggests
that the group were satisfied with the current user interface
for ease of policy experimentation, but as an aid to supervisory
learning it needed to be more visual.
The Behaviour of the Model
The interviewees were asked whether they were surprised about
any of the behaviour of the simulation output;
"It's interesting to see which ones [policies]
affect [the behaviour of the model], and I suppose we could concentrate
on basically the ones which we could influence the most, quickly
and cheaply . . . get as many people involved." [Production
"Getting over the credibility gap, let's say
you've got a group, say we looked at departments one and two,
and you have that group of managers and supervisors, they think
the model's credible, we've reached that point it would allow
them to understand safety." [Safety Professional]
The safety professional describes how he argues often with the
production management group about safety issues, and they complain
that they can't fit enough guards on machines;
"Sure if it should be guarded it should be guarded,
but to expect that to make a tremendous inroad into accident rates
is false. It's what people do that cause accidents. A blend of
on-the-job and off-the-job training is required . . . it is generally
accepted that training has that benefit, and you have a factory
where the guarding is not adequate and hardly any accidents, and
then you can have the converse where you can have everything guarded
and lots of accidents. The difference there is the people."
Comments were made about the interesting nature of the model's output, and the ease with which policy experimentation could be conducted. The safety professional agreed that he was aware from experience that training would have a major impact upon safety, and that the model confirmed his opinion.
How to Convince Senior Management of the Model's Worth ?
Whether strategies identified in the model could ultimately be
pursued would depend on the safety budget. This would be set by
the senior accountants and board members. Safety would have to
be sold as a cost centre to these people. The group was queried
as to their perceived judgement of senior management's response
towards the usefulness of the model;
"if you've got a group of directors . . .they
are not at the technology end. So for a start it's a computer
and they're not entirely familiar with that and then you've got
the scepticism about modelling which would be a concept with which
they would maybe not be familiar. I think there would be a point
where they would say 'Well very interesting but I'm too busy,
go talk to someone else'. So before you've got over those two
hurdles to get the benefits of the model they might have gone
and lost interest . . . they've got to the bullet points [model
summary], they want to be there, if the bullet points don't confirm
their pre-digested thinking, their own prejudices and beliefs,
then you're obviously wrong and they move onto something else."
"But saying that if the bait's taken with a few bullet points then all of a sudden you find that they're running very fast to the beat . . .
The best place to target is the accounts, accountants."
"That might be the best place to start . . .
general mistrust about computers, no knowledge about modelling.
I think that's where we are, and most companies might be like
that." [Safety Professional]
The group offered a range of opinions on the perception of senior
managers. To use the model in a demonstration capacity seemed
to be the opinion of the group. Selling the concept and the power
of the model for safety evaluation would have to be done carefully,
as there appeared to be some doubt about the open mindedness of
the senior managers.
Exploring Alternative Strategies Not Covered by the Model
The group were questioned as to whether they believed that the model policies covered the fundamental influences on safety;
"What about incentive schemes ? You could have that as an additional policy" If you had a slider bar, pounds (£'s) per month per employee invested in the safety scheme. Then you've got a cost . . .
It could have a similar effect to training."
This statement from the safety professional strongly suggests
that he has a good grasp of the structure of the model despite
having minimal contact with it. He was able to identify a key
input as units per unit per time. He saw the potential to evaluate
policy by the addition of a viable policy and identified its dimensions.
This was an observation about how the model could be re-engineered
in order to improve policy evaluation;
"Management competence . . . their competence in safety could be measured and some term found which you could vary to influence the model . . .
If you've got ignorance on the part of the senior
people and an unwillingness to act that would have massive effects
on how your company performs, well in any sphere." [Safety
It was explained that management competence was indirectly included
in the model as the policy decisions actually taken would be those
of the management.
The Model as an 'Edutainment' Game
The role of the model as an 'edutainment' game was raised and
responses were short but encouraging;
"somebody who is enlightened in safety using it [the model] as a policy tool, whereas, a person from a more general background using it as an educational or edutainment tool ?
I think as an edutainment tool people would be more
inclined to play with it [the model], and it's playing with it
you actually learn." [Safety Professional]
The observation that the longer people played or experimented
with the model, the more they would learn was very astute. This
shows that the manager believed in the ability of the model to
help people to learn about safety through teaching themselves.
Optimisation of the Model
Optimisation was an area brought up directly by the group. They
were probing to discover if the model could be optimised, and
if so how ?
"Could it be programmed to work out itself what
the most effective variables are in the model ?" [Management
"An optimising program, would you set the target
of minimising all costs ?" [Safety Professional]
It was explained that the model had been manually optimised to
identify a policy mix which would minimise costs. It was pointed
out that optimisation programmes were available with certain system
The question of removal of human interaction by using an optimisation
program was raised by the interviewer. It was suggested that people
may not get the opportunity to explore policies if they were to
let the computer make the decisions for them;
"If there was a function you could just switch on and off then you could just use it for both . . .
Like for somebody who was familiar with the model and believed what it told them . . . he'll want to run the optimisation won't he ? He won't want to spend hours in front of the keyboard . . .
But you want the learning course because it might be that the optimisation will have to take account of the amount of money you have available or the amount of time, so you want to optimise given that these inputs must be maintained below this level. So what can we do with the resources we've got ? . . .
"That's an interesting philosophical debate.
Do you want to optimise on accidents, which is zero accidents,
or do you optimise on cost and you might not choose zero accidents
?" [Safety Professional]
Optimisation was seen as useful for policy making, in fact an interesting discussion ensued as to whether the model should be optimised on accident rates or safety costs. Certainly the group were thinking here purely in policy-making terms.
Who would use the Simulation and for what Purpose ?
One question posed to the group was;
"Would they use the model to enlighten other
people ?" [Interviewer]
"From top to bottom really" [Production
"I think there's still work to do on enlightening, because we can still slip back into 'Well I can't get enough fitters to fit the guards . . . I can't do anything about safety.' . . .
It would be for anybody to come and use it, it would
be for learning, once you've achieved that aim, you could then
use it by adding features to mould it into a policy tool, but
first of all it must be a good learning tool" [Safety Professional]
Abstract or 'Real World' Model ?
The group were asked their opinion on using an abstract model
or one validated with their companies data;
"It [an abstract model] would still help us
to learn and we might discover policies that we would not normally
discover." [Safety Professional]
"If you took it off a really successful firm,
like a Japanese leader, something not necessarily in this industry."
"You could switch on the generic model, which is designed to show how safety works for any company . . . introducing policies and switching them on. If people played with that the next thing they would want is something they could use for their own situation." [Safety Professional]
Summary of Discussion Findings
A wide range of views were put forward by the three interviewees,
all possessing varying knowledge of occupational safety and simulation
models. The common thread that can be teased out of the discussion
is that the model in its present form was found to be helpful
by the group for understanding the firm's occupational safety
Many of the explicit observations made by the group pointed to
the model being more suitable as a tool to either demonstrate
the effects of safety policy, or to assist people in learning
more about the company's safety system. There was acknowledgement
that the simulation would still be of value in learning or even
policy making when set in an abstract context, although there
was a greater appreciation of the model in its present 'real world'
form. Much of the underlying discussion pointed towards using
the model to assist with policy evaluation. Suggestions were made
concerning the introduction of other policy parameters into the
The results of the policy experiments that the group conducted
were certainly pertinent to the discussion. Training was suggested
by the model as the policy most able to exert either a virtuous
or vicious effect over the whole system. The model had allowed
the interviewees to appreciate this and much debate had followed
as to how training might best be used.
The group had considered carefully the initial query put forward,
i.e. learning or policy tool ? This allowed the interviewer to
elicit quite a rich picture of opinion on the uses of the model
in their safety environment and beyond.
Forrester, J.W. and Senge, P. 1980. Tests for Building Confidence in System Dynamics Models. ed.'s A.A. Legasto, J.W. Forrester and J.M. Lyneis. In Studies in the Management Sciences: System Dynamics 14: 209-228. Amsterdam: North-Holland.
Moizer, J.D. 1994. Safety Hazard Control in the Workplace: A Dynamic Model, Information Systems. Proceedings of the 1994 International System Dynamics Conference, Stirling, UK.
Moizer, J.D. 1996. Safety Knowledge and its Influence over Accidents in the Workplace, Proceedings of the 1996 International System Dynamics Conference, Boston, MA.
Sterman, J.D. 1983. Appropriate Summary Statistics for Evaluating the Historical Fit of System Dynamics Models, Proceedings of the 1983 International System Dynamics Conference, Pine Manor College, Chestnut Hill, MA.
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