Seyyed Ali Moussavi-Najarkola AJE Vol.9 2009 63-78
70
Lack of enough recovery periods hour
0 1 2 3 4 5 6 7 8
Multiplier factor 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3
Table 9. Elements for achieving the multiplier factor for age factor AF
Age rating year
≤ 40 41-50
51-60 60
Multiplier factor 0.6 0.8 0.9 1
3.8. Lack of Recovery Periods RP
A recovery period is defined as “period of time between or within cycles, during which no repetitive movements are carried out” 10. A recovery period
consists of relatively long pauses after periods of mechanical movements; during these periods muscles can recoved metabolically 10. Lack of recovery periods can
create oxygen debt and produce accumulation of lactic acid, which induces muscle fatigue 4. Therefore, providing formal and informal rest intervals between work
cycles during tasks can prevent muscle fatigue and UEMSDs 1, 3, 5. The multiplier factor for lack of recovery period Table 8 was derived from 15 and 16 using the
OCRA method 10.
3.9. Age Factor AF
Age is the most important factor in force exertion and biomechanical models 18; it has a direct relationship with FE and Maximal Aerobic Capacity in hand
activities 4. For example, a 40 year old person has the maximal power, but at later ages this capability and power decrease slowly 18. The age factor multiplier Table
9 was obtained using the European Coal and Steel Community ECSC studies that quantified the effect of age on inducing and exacerbating UEMSDs 21, 22, 23.
3.10. Effective Item EI
EIs are factors that have indirect effects on the incidence rate of UEMSDs 10.These items may be present in repetitive tasks, but not necessarily or always
10. Their type, intensity and duration lead to an increased level of overall exposure to risk of developing UEMSDs 2. These items are considered to be relevant in the
production and development of UEMSDs 3. They are always work-related, and must be considered when assessing risk exposure 5. For an item to be considered,
it must have an association with UEMSD occurrence, so that it would have a collective impact rather than an individual impact 10. To obtain EI, a score of 1 is
allocated to any item whenever that item is present 10.
• Extreme precision at working
Chronic Exposure Index Model to Assess Ergonomic Risk Factor Related to Upper Extremity Musculoskeletal Disorders
71 • Unsuitable lighting low or
high • Exposure to heat
• Carelessly • Economic problems
• Background of UEMSDs • Localized compression on
upper limb • Lack of training
• Secondary job • Reach limit
• Clearance • Humidity
• Poor size or shape of parts • Presenting vibration
• Exposure to cold • Presenting noise
• Low experience • Familiar problems
• Contact stress • Sharpness of object surface
• Rapid twistingturning movements
• Overtime • Slippery level
• Poor packaged goods or poor handles
• Chemical components and poisons
• Hand-arm vibrations
Then, the scores are added and the corresponding multiplier factor is determined Table 10, which was calculated from 15 and 16 studies using the
OCRA method 10.
4. Development of the CEI
UEMSDs are generally agreed to be a multi-factorial occupational problem 24. Many epidemiological studies have linked development of UEMSDs to various risk
factors 25, 26, 27, 28, which have been classified into physical 29, psychosocialorganizational 30, 31, 32, and individual 33 occupational risk
factors.
Several ergonomic techniques have been developed to assess exposure UEMSD risk factors 34. Many of the posture–based observational techniques which have
been provided are only strictly applicable in very limited circumstances and have shortcomings and limitations. Based on these findings and current techniques, a
strategy and policy was developed to obtain a CEI which:
a Is applicable to the complete range of manual tasks; b Provides an integrated assessment of various risk factors;
c Provides an independent assessment of disorder risk to different body regions; dProvides an overall risk assessment which allows prioritisation of tasks and
submits suggested action levels; eFacilitates effective targeting of controls by providing an indication the relative
severity of different risk factors within a task; f Is suitable for use by workplace staff with minimal training and equipment;
g Is quick and easy to use; and h Can identify high risk manual handling and repetitive tasks
