Comparative occupational risk assessment in a CNC machine tool operator position

Abstract

Law requires from employers to assess occupational risk in workplaces. A well-executed occupational risk assessment promotes the improve-ment of working conditions and reduces a negative impacts on employees’ health and life. Employers by conducting occupational risk assess-ment not only meet legal requirements but also benefit from it in two ways. They eliminate loss of an enterprise connected with employees’ absence, and they also decrease the probability of high compensation pay due to situations that have a destructive influence on the employees’ health. However, in order to benefit from such actions, firstly, it is necessary to select a risk assessment method properly, then to apply it and implement preventive measures. The paper presents the results of the occupational risk assessment carried out on the example of a CNC ma-chine operator by means three-stage methods in accordance with the PN-N-18001, PHA and Risc Score. Despite the subjectivity of the assess-ment, there were differences in the results. Thus, it is advisable to choose a risk assessment method skilfully, for example by comparing several similar methods.

Full text

ARCHIWUMINŻYNIERIIPRODUKCJI 28
PRODUCTIONENGINEERINGARCHIVES16(2017)28‐31
PRODUCTIONENGINEERINGARCHIVES
ISSN 2353-5156 (print)
ISSN2353-7779 (online) Exist since 4th quarter 2013
Available online at www.qpij.pl/production-engineering-archives
Comparative occupational risk assessment in a CNC
machine tool operator position
Andrzej Pacana1
1Rzeszow University of Technology, Faculty of Mechanical Engineering and Aviation, al. Powstancow Warszawy 8, 35-959 Rzeszow,
Poland, e-mail: app@prz.edu.pl
Article history
Received 17.05.2017
Accepted 12.09.2017
Available online 30.10.2017
Abstract
Law requires from employers to assess occupational risk in workplaces. A well-executed occupa-
tional risk assessment promotes the improve-ment of working conditions and reduces a negative
impacts on employees’ health and life. Employers by conducting occupational risk assess-ment not
only meet legal requirements but also benefit from it in two ways. They eliminate loss of an enter-
prise connected with employees’ absence, and they also decrease the probability of high compensa-
tion pay due to situations that have a destructive influence on the employees' health. However, in
order to benefit from such actions, firstly, it is necessary to select a risk assessment method properly,
then to apply it and implement preventive measures. The paper presents the results of the occupa-
tional risk assessment carried out on the example of a CNC ma-chine operator by means three-stage
methods in accordance with the PN-N-18001, PHA and Risc Score. Despite the subjectivity of the
assess-ment, there were differences in the results. Thus, it is advisable to choose a risk assessment
method skilfully, for example by comparing several similar methods.
Keywords
Methods of occupational
risk assessment
CNC machine tool
occupational risk
1. Introduction
Occupational risk assessment is a primary prevention and
health task in every workplace. This assessment is mainly
intended to ensure the safety of employees and to eliminate
or partially reduce existing threats by taking appropriate
remedies. Employers, by carrying out occupational risk as-
sessments, in their workplaces not only meet legal require-
ments, but also they benefit in two ways: they eliminate
companies' loss related to absence of employees and to the
need to pay high compensations in cases that are destructive
for employees' health. Therefore, identifying hazards at every
workplace is an extremely important part of an appropriate
health and safety policy. Correctly estimated likelihood and
risk tolerance statement of a particular risk, make employers
and workers aware of how important it is to use health and
safety regulations in everyday work circumstances and to use
appropriate protection measures to prevent or minimize pos-
sible consequences of unforeseen dangerous situations.
(ULEWICZ R., ŻYWIOŁEK J. 2016, KABER D., ZAHABI M.
2017)
Occupational risk assessment is not a one-time process but
a repetitive one. If changes have been made to the organiza-
tion of work, requirements, protective measures using or new
equipment or materials have been introduced, a risk assess-
ment process should be repeated. An occupational risk as-
sessment process should also be repeated if it is necessary to
reduce the risk after the assessment was carried out, of
course, after a prior selection and the application of appropri-
ate safety measures. An occupational risk assessment should
be performed by a team of at least two people, and, also, with
appropriate knowledge and experience in this area. (KRAUSE
M. 2011, WOŹNY A., PACANA A. 2014, NOWICKA-SKOWRON
M., ULEWICZ R. 2016)
The methodology of conducting occupational risk assess-
ment includes 4 main steps: collecting information, identifi-
cation of hazard, occupational risk evaluation and determina-
tion of occupational risk admissibility (PN-N 18002:2011).
There are many methods of occupational risk assessment,
therefore, subject literature divides the methods of occupa-
tional risk assessment. Current division of methods include
dividing into inductive and deductive, and quantitative and
qualitative methods. It is important to select an adequate
method out of such a variety to properly assess occupational
risk in a particular workplace. Employees responsible for
safety and health, sometimes try to use one risk assessment

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methodology for all job positions. It is not the most advanta-
geous solution, as there are various risks in different work-
places (ROMANOWSKA-SŁOMKA I., SŁOMKA A. 2104)
What is more, for example, there are different types of
dangers that occur in locations where conventional cutting
machines and CNC machines are situated. Hence, it seems
advisable to diversify methods of risk assessments according
to the risk in different positions and, at the same time, to
discover as adequate as possible for a specific position. An
attempt to do this is presented in the paper in relation to the
position of the operator of numerically controlled machines.
2. Characteristic of the position of CNC
machine operator
Machine toll-controlled with a computer (CNC) performs
automated processing with CNC computer control. The
computer integrated with a system takes over the whole con-
trol process as well as the control functions of the machine.
This computer supervises all the movements in the machin-
ing process, machining parameters and auxiliary operations
so as to obtain the product with the de-sired features of
shape, dimension and specific surface. These facts affect the
specific hazards of this workplace. A CNC machine toll
operator should have appropriate qualifications. (RACHIERU
N., BELU N., ANGHEL D.C. 2015, YIN C., ET AL. 2013, ZHU
X.C., ET AL. 2013, LESTYANSZKA-SKURKOVA K. 2017)
Work at the operator's station is an individual work, typi-
cally 8 hours, sometimes shifted. This work requires a long
period of focus, both visual and auditory concentration. Dur-
ing work, there may be increased energy expenditure, mo-
notony of activity, monotonous position of the body. It is for-
bidden to wear loose clothing while working at the operator
station. The microclimate of work can most often be assumed
to be stable, which is beneficial for the tasks performed. The
work should be performed in a closed, heated, well exposed
and ventilated room.
Working as a CNC machine operator's connected with the
risk of both dangerous and harmful or disruptive factors.
Their occurrence is likely to result in an accident at work and
it is imperative that an operator must follow the required
health and safety measures every day.
Performing work in the operator's CNC ma-chine position
is associated with the occurrence of dangerous mechanical
factors causing injuries. Examples include moving parts of
used machines, falling machine parts or hot surfaces. Haz-
ardous substances also include the dangers of electric shock.
The harmful factors occurring during the work in the opera-
tor position of CNC machines are, for example, noise and
vibration, oil mists or grinding dusts, and temperature and
humidity of the air. The onerous factors affecting the opera-
tor of a numerically controlled machine tool may include
many hours of standing work, stress and physical exertion.
Negative effects of such threats entail, but are not limited to,
tendons and backbone injuries, limb injuries, but also psy-
chological stress.
3. Risks at the position of CNC machine tool
operator
Risks in a particular workstation after being identified
should be classified. Danger that was identified in CNC
machine tool operator's work-place is presented in the Tab. 1.
It was supported with the Polish standard PN-N-18002 and
the guidelines of the Polish Labor Inspection (PIP) (GÓRSKA
E. 2012., PN-N 18002:2011, WOŹNY A., PACANA A. 2014).
Protection measures are omitted in the table since the infor-
mation is available in the literature.
Table 1. Threats identified at CNC operator position
No SOURCE EFFECTS
1 moving parts of used ma-
chines contusions, injuries
2 moving machine elements and
objects pinching, pressing
3 sharp, protruding and rough
objects injuries, cuts, abrasions
4 falling elements of machines pinching, pressing
5 slippery, uneven surfaces
Injuries caused by slipping,
tripping and falling due to
technological fluid leakage
or substrate inequality
6
situation of the position with
respect to the ground
fall from the heights, inju-
ries, contusions
7 hot or cold surfaces corrosive
substances burns
8 electric shock paralysis
9 hand tolls
cuts, abrasions, contusions,
infections due to contamina-
tion of small abrasions plac-
es and small injuries
10
noise emitted by machine
tools, mechanized and hand
tools and activities performed
in the production hall
Noise, damage or even
hearing loss
11 heavy elements moving and
lifting contusions, injuries
12 forced body positions at work
Contusions, injuries, back-
bone pain
13
work stress: overtime, night
work, employees' conflicts,
forced work rate, long monot-
onous work
stress, psychological trauma
14
exposure to harmful chemi-
cals (oil mist and grinding
dust)
infections and respiratory
diseases, eye irritation,
pollination with dust, grit
and curls
15 Low or high temperature on
the workstation
cold, chilled body, overheat-
ing of the body
16 fire burns, injuries, poisonings
17 explosion burns, injuries

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4. Occupational risk assessment of CNC
machine operator
As a method proposed for occupational risk assessment on
a CNC machine operator position, a three-stage method ac-
cording to PN-N-18002, a Risc Score method and a PHA
method were chosen. The methodologies are described in the
literature of the subject, for example (GÓRSKA E. 2012,
KRAUSE M. 2011, ROMANOWSKA-SŁOMKA I., SŁOMKA A.
2104, WOŹNY A., PACANA A. 2014).
In case of assessment based on the PN-N-18002 standard
all risks have been classified into five groups, followed by
probability and severity of consequences. Then, using the
(WOŹNY A., PACANA A. 2014), the value of a risk and its
admissibility in acceptable and unacceptable categories were
determined (Tab. 2).
Table 2. Occupational risk assessment of CNC machine operator
according to the PN-N-18002 standard
No Threat Probabili-
ty (P) Effect (S) Risk
Result Admissibility
1 Contusions small medium 1 admissible
2 Injuries small medium 1 admissible
3 Burns small medium 1 admissible
4 Noise big medium 3 impermissible
5 Infections,
diseases small small 1 admissible
6 Stress medium medium 2 admissible
7 Pollination small medium 1 admissible
The average value of risk occurring at the CNC machine
operator's position, estimated with the PN-N-18002 standard
is 1.25. It means that it is defined as small, so the risk is
admissible.
Table 3 shows the results of the conducted occupational
risk assessment of a CNC machine tool operator using the
Risc Score method.
Table 3. Risk assessment of the CNC machine operator with use of
the Risk Score method
No Threat Probabili-
ty (P)
Expo-
sure
(E)
Ef-
fect
(S)
Risk (PxExS)
Value Category
1 Contusions 6 6 3 108 Significant
2 Injuries 0,5 3 3 4,5 Acceptable
3 Burns 0,5 2 3 3 Acceptable
4 Noise 10 6 1 60 Small
5 Infections,
diseases 0,2 0,5 3 0,3 Acceptable
6 Stress 3 3 3 27 Small
7 Pollination 0,5 1 3 1,5 Acceptable
The average value of the risk in position of CNC operator
calculated with use of the Risc Score method is 29.2, that
according to the categories of this method qualifies it as
acceptable, in a scale of: very big, big, significant, small and
acceptable.
Table 4 presents the occupational risk assessment of CNC
machine tool operator, performed with use of the PHA meth-
od.
Table 4. Occupational risk assessment of CNC machine tool opera-
tor by the PHA method
No
Threat
Probabi-
lity (P)
Size of
damage
(S)
Risk
Value
(PxS) Category
1 Contusions 4 1 4 permissible
2 Injuries 3 1 3 acceptable
3 Burns 2 2 4 permissible
4 Noise 6 2 12 unacceptable
5 Infections,
diseases 1 2 2 acceptable
6 Stress 5 1 5 permissible
7 Pollination 4 2 8 permissible
The average value of risk at the workplace of numerically
controlled machine tools, calculated by the PHA method, is
5.4. It is defined as permissible in a scale of acceptable, per-
missible and unacceptable.
In the next step, the obtained results of the occupational
risk assessment were compared and presented in Tab. 5.
Tabela 5. Comparison of occupational risk assessment.
No
Identified
threat
According to
the PN-N-
18002 stand-
ard
Risc Score
method
PHA method
1 Contusions permissible significant permissible
2 Injuries permissible acceptable acceptable
3 Burns permissible acceptable permissible
4 Noise unacceptable small unacceptable
5 Infections,
diseases permissible acceptable acceptable
6 Stress permissible small permissible
7 Pollination permissible acceptable permissible
The conducted with three methods occupational risk as-
sessment determines the operator's occupational risk as ac-
ceptable, but there are differences in the results that may
indicate the choice of an adequate risk assessment method.
5. Summary and conclusion
As a result of the occupational risk assessment, it can be
observed that, according to all risk assessment methods that
were used, the risk of injuries, burns, infections, diseases and
pollination is permissible and acceptable. Differences occur

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in the case of dangers related to the occurrence of stressful
situations. In accordance with the PN-N-18002 standard and
with the PHA method a risk is permissible, while the Risc
Score method identifies it as small, that indicates the need to
periodically controlling the intensification of negative ef-
fects. Another difference occurs in case of threat of injuries
and contusions. The Risc Score method, as the only one of
the analyzed methods, classified these threats as significant,
and therefore suggests actions to minimize the impact of this
harmful factor. Noise has been classified similarly in each of
the three methods analyzed. Nevertheless, it is worth to note
that the most radical method for this occupational risk as-
sessment at CNC operator position is the Risc Score method.
In spite of the simplifications and assumptions that were
made in hereby paper, the Risk Score method can be pro-
posed to assess occupational risk for this workplace.
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数控机床操作员职位的比较职业风险评估
关键词
职业方法
风险评估
数控机床
职业风险
抽象
法律要求雇主评估工作场所的职业风险。执行良好的职业风险评估有助于改善工作条件，减少
对员工健康和生活的负面影响。雇主通过职业风险评估不仅符合法律要求，而且从两方面受
益。消除与员工缺勤有关的企业的损失，并且由于对员工健康造成破坏性影响的情况，也降低
了高薪酬的可能性。但是，为了从这些行动中受益，首先必须适当选择风险评估方法，然后实
施并实施预防措施。本文以 PN-N-18001，PHA 和 Risc 分数为依据，采用三阶段方法，对数控
机床操作员实例进行职业风险评估的结果。尽管评估的主观性，结果有差异。因此，建议您巧
妙地选择风险评估方法，例如通过比较几种类似的方法。