Occhipinti E, Colombini Daniela, Occhipinti M
Unità di Ricerca EPM (Ergonomia della Postura e del Movimento), Fondazione IRCCS Ospedale Maggiore Policlinico Ma-Re.
Med Lav. 2008 May-Jun;99(3):234-41.
In the Ocra methods (Ocra index and Ocra Checklist), when computing the final indices (Ocra index or checklist score), in the case of more than one repetitive task a "traditional" procedure was already proposed, the results of which could be defined as "time-weighted average". This approach appears to be appropriate when considering rotations among tasks that are performed very frequently, for instance almost once every hour (or for shorter periods). However, when rotation among repetitive tasks is less frequent (i.e. once every 1 1/2 or more hours), the "time-weighted average" approach could result in an underestimation of the exposure level (as it practically flattens peaks of high exposures). For those scenarios an alternative approach based on the "most stressful task as minimum" might be more realistic. This latter approach has already been included in the NIOSH approach for multiple sequential lifting tasks and, given the recent availability in the Ocra method of more detailed duration multipliers (practically one different Du(M) for each different step of one hour of duration of the repetitive task), it is now possible to define a particular procedure to compute the complex Ocra Multitask Index (cOCRA) and the complex Checklist Score (cCHESCO) for the analysis of two or more repetitive tasks when rotations are infrequent (rotations every 1 1/2 hours or more). The result of this approach will be at least equal to the index of the most stressful task considered for its individual daily duration and at the most equal to the index of the most stressful task when it is (only theoretically) considered as lasting for the overall daily duration of all examined repetitive tasks. The procedure is based on the following formula: Complex Ocra Multitask Index = Ocra(1(Dum1) + (Delta ocra1xK) where 1,2,3,...,N = repetitive tasks ordered by ocra index values (1 = highest; N = lowest) computed considering respective real duration multipliers (Dum(i)). ocra1 = ocra index of task, considering Dum(1). Dum(i) = duration multiplier for task(i) real duration. Dum(tot) = duration multiplier for total duration of all repetitive tasks. delta ocra1 = highest ocra index among N tasks considering Dum(tot) (ocra(i max)) - ocra index of task1 considering Dum1. K = (ocra(1 max)*FT1) + (ocra(2 max)*FT2) + ... + (ocra (N)*FT(N)) over (ocra(i max)). ocral,Nm(1,N MAX) = index of tasks 1 to Ncons idering Dum,, (tot)7=Fr(i) c tion of Time (values from 0 to 1) of task; wi(i)h respect to the total repetitive time.
在Ocra方法（Ocra指数和Ocra检查表）中，在计算最终指数（Ocra指数或检查表得分）时，对于不止一项重复性任务的情况，已经提出了一种“传统”程序，其结果可定义为“时间加权平均值”。当考虑非常频繁执行的任务之间的轮换时，例如几乎每小时（或更短时间段）执行一次，这种方法似乎是合适的。然而，当重复性任务之间的轮换频率较低时（即每1.5小时或更长时间一次），“时间加权平均值”方法可能会导致对暴露水平的低估（因为它实际上会平滑高暴露峰值）。对于这些情况，基于“最具压力任务取最小值”的替代方法可能更现实。后一种方法已被纳入NIOSH针对多个连续起重任务的方法中，并且鉴于Ocra方法中最近可用的更详细的持续时间乘数（实际上，对于重复性任务一小时持续时间的每个不同步骤都有一个不同的Du(M)），现在可以定义一个特定程序来计算复杂的Ocra多任务指数（cOCRA）和复杂检查表得分（cCHESCO），用于分析当轮换不频繁时（每1.5小时或更长时间轮换一次）的两项或更多项重复性任务。这种方法的结果至少等于考虑其个体每日持续时间的最具压力任务的指数，最多等于当（仅在理论上）将其视为持续所有检查的重复性任务的总体每日持续时间时最具压力任务的指数。该程序基于以下公式：复杂Ocra多任务指数 = Ocra(1(Dum1) + (Delta ocra1xK)，其中1,2,3,...,N = 按Ocra指数值排序的重复性任务（1 = 最高；N = 最低），根据各自的实际持续时间乘数（Dum(i)）计算得出。ocra1 = 考虑Dum(1)时任务的Ocra指数。Dum(i) = 任务(i)实际持续时间的持续时间乘数。Dum(tot) = 所有重复性任务总持续时间的持续时间乘数。delta ocra1 = 考虑Dum(tot)时N项任务中最高的Ocra指数（ocra(i max)） - 考虑Dum1时任务1的Ocra指数。K = （(ocra(1 max)*FT1) + (ocra(2 max)*FT2) +... + (ocra (N)*FT(N))）除以(ocra(i max))。ocral,Nm(1,N MAX) = 考虑Dum,, (tot)7=Fr(i)时任务1到N的指数；wi(i)h相对于总重复时间的任务时间（值从0到1）。
