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changes on the work design should be held. This procedure is extended also to multi-task manual
lifting jobs by calculating the overall LI (Composite Lifting Index - CLI) (NIOSH, 1994).
The lifting model proposed by Hidalgo et al. (1997), is a multiplicative model based on the revised
NIOSH equation (Waters et al., 1993) using for lifting tasks. The equation estimates the personal
lifting capacit (PLC) and the general lifting capacity (GLC) by taking into consideration several
additional multipliers:
LC = (WB ) × (H) × (V ) × (D) × (F ) × (T D) × (T ) × (C) × (HS) × (AG) × (BW )
where AG is the age factor (yrs), HS is the heat stress (wet bulb globe temperature), TD is the task
duration (hrs), WB is the maximum load acceptable to different percentages of worker population
(kg), BW is the body weight (kg), and H = HM, V = VM, D = DM, T = AM, F = FM, C = CM (see
Eq. (1.1)). The multipliers have been adjusted in order to accommodate others percentiles more
than the 75% of the females and 90% of the males workers that NIOSH lifting equation assume.
New multipliers have been introduced in order to be gender-, age-, and fitness-based specific. The
authors argued that the model is adequate to be used also for back-to-work decisions.
The EN 1005-2 (2009) standard, applies to the manual handling of machinery, components parts
of machinery and objects processed by the machine (input/output) of 3 kg or more. Like in the
NIOSH approach it provides a risk index (R I ) which is calculated as the ratio between the actual
mass to the recommended mass limit (R M L ). The recommended mass limit is estimated by an
equation which is based to Eq. (1.1) where three more multipliers have been added:
RM L = RW L × (OM ) × (P M ) × (AT )
where OM is the one handed multiplier (if true OM = 0.6, otherwise OM = 1), PM is the two person
multiplier (if true PM = 0.85, otherwise PM = 1) and A T is the additional task multiplier (if true
A T = 0.8, otherwise A T = 1). If the risk index is lesser than 0.85 the risk may be regarded as
tolerable. When 0.85 < R I < 1.0 there is a significant risk of injury to the operator(s) and it is
recommended the redesign of the machinery or to ensure that the risk is tolerable. If R I ≥ 1 it
means that redesign is necessary, so the design can be improved by changing the multipliers.
Grieco et al. (1997), modified the multipliers of the NIOSH lifting equation in order to contemplate
a large number of possible major risk factors (Fig. 1.10) many of which are listed in the Annex to
EC Directive 90/629 (1990). The model uses the NIOSH lifting equation but it includes a further
discount of 0.6 for one-arm-lifting and 0.85 for more than one operator lifting. Moreover, there is
a discount for workers who have WRLBD according to their gender (Fig. 1.10).
Since the other multiplicative models mentioned above can used only for lifting tasks, Shoaf et al.
(1997) proposed a multiplicative model similar to NIOSH lifting model but for evaluating lowering
tasks in combination with pushing, pulling, and carrying tasks. The model is an adaptation of
Snook and Ciriello (1991) psychophysical tables but incorporating biomechanical and physiological
sources of stress. The equation estimates the lowering capacity (LOC) as: