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We are often subject to handling, whether in an office or in production. These handlings represent the majority of MSD and accidents.

Introduction

The wearing of manual loads by a person is an essential notion in ergonomics, most of us being subject to it. The bearing of the loads here taken into account are the uplifts from the ground and the load shifting on the horizontal plane, the two being frequently associated.

Surveys show that 4 out of 101 employees handle loads daily. Moreover, statistics show that these movements are among the main causes of accidents at work (1 of 3) and professionnal diseases (3 out of 4)2.

The risks

The risks associated with these actions are mechanical as well as cardiovascular, but also the fall of these same objects. Too much effort can lead to herniated hernias, but if the load is properly manipulated, improper control of this load can lead to abnormal efforts.

In women, abdominal overpressure due to abnormal exertion can generate genital prolapse (especially in women with maternées) and varicose veins.

The principle

The NF X35-109 standard defines different stress-acceptance thresholds according to painfulness and capacity parameters. For this, an experiment was conducted with 147 people trained in handling. Their objective was to choose the weight that best suited them to lift a load from the ground at a height of 60 cm twice per minute. This choice had to meet two criteria: to work to the maximum by imagining to be paid for performance and not to cause fatigue or lumbar pain.

The norm goes beyond European and international standards. Since they cannot make a difference between men and women, they define identical thresholds for all. These thresholds are: 5, 15 and 25 kg regardless of sex and age.

The standard takes into account these differences in capacity to define different categories of thresholds that we find below:

Type of activity

Age

Sex

Permissible weight in Kg

Occasional

15 to 18 years

Man

15

Woman

12

18 to 45 years

Man

30

Woman

15

45 to 65 years

Man

25

Woman

12

Regular

15 to 18 years

Man

12,5

Woman

10

18 to 45 years

Man

25

Woman

12,5

45 to 65 years

Man

20

Woman

10

These different thresholds have been calculated for the following conditions beyond which a coefficient of adjustment will have to be applied. The following standard conditions are found:

  • Catch or drop height between 0.75 – 1.10 m.
  • 2m lower displacement Distance.
  • 1 handling every 5 minutes maximum.
  • Absence of constraints linked to difficult working conditions (lack of light…), related to the environment or to the organisation of work.

The whole study is based on the fact that we are going to compare the thresholds of the norm with our situation.

It is pointed out that the standard defined thresholds both for a “ one-off” comparison where the threshold is compared with our object, and for actions on a day of work where we will compare specific thresholds expressed in tonnage. As part of this article, we will only deal with the first case.

1.1-Make the statement

The first step is to do the reading. The standard provides a whole range of questions that will allow us to define the maximum acceptable weight associated with our work situation. The questions are divided into 5 groups defined below.

The first reading will define the type of movement we perform. For this, the standard gives us a grid that defines the coefficients of adjustments according to the position in the space of the object to be lifted or posed.

The color code reading is as follows:

1.2 – Movement parameters

We’ll define the parameters of the movement. We’ll answer the questions:

  • What is the average weight of our object?
  • is the handling done with 1 or 2 hands?
  • What is the distance on which the object is moved?

Also, the answer to these questions allows us to define adjustments to reduce or increase the effort associated with the movement.

1.3 – The conditions of the movement

Other group of questions, the conditions under which the handling is carried out. We’ll find five questions:

  • Is the grip of the object easy or not? In the clear, are there handles adapted to this one to allow us to maneuver it easily.
  • Is the load large?
  • Does the movement take place with a twist of the trunk?
  • is the load unstable or fragile?
  • Are we in a sitting position or not?

1.4 – The Working environment

Here too a series of questions allow us to define a coefficient to adjust the painfulness. We find seven questions:

  • Do we work in thermal, hot or cold, specific conditions?
  • Is there a lot of noise?
  • is the lighting suitable?
  • Is there a lot of vibration?
  • Is the atmosphere dusty, dirty?
  • is the soil degraded (oil, hole…)?
  • Is the area congested?

1.5 – The organization of work

Finally, last point allowing us to adjust the painfulness, the constraints related to the organization. There are 4 of them:

  • Are we “in a hurry ” to make the move?
  • Do we have to do the movement in a certain way (because limited by machines or other), or are we free?
  • Do we have to do another task at the same time (keep the production file of the part…)?
  • Are there any specific quality requirements related to the object?

2-Calculating the equivalent constraint

Once the set coefficient of adjustment is defined, we will calculate the equivalent constraint of our movement. In fact, the thresholds defined by the standard depend on the working conditions. We have with regard to the previous step, defined our working conditions and we will use them to adjust the standard threshold value. The process is the following.

2.1-Definition of the 2 lowest coefficients

Among the previous coefficients (the coefficient associated with the fact that the movement is done with one or two hands, considered by the norm as the most critical), the product of the two lowest coefficients will be carried out.

2.2 – Deduct the equivalent load

From there, we will calculate the equivalent load according to the following formula:

Average load weight / (1st small adjustment value X 2nd small adjustment value) / One-hand handling adjustment coefficient

It is understood that the equivalent load will necessarily be equal to or greater than the initial weight of our element. Indeed, it is easy to understand that, depending on “degraded” conditions, the associated effort is more important.

2.3 – Set the ” threshold ” value in terms of our conditions

To find out if we are ” in the norm “, we will adjust the value of the table of the standard according to our conditions. We will define whether the activity is occasional or not, whether it is a woman or a man who makes the move and finally how old is this person. Depending on these criteria, we will define a new qualifying ” weight ” under our conditions.

3 – Conclusion

The study will consist of comparing the load equivalent to the threshold value calculated under our conditions:

  • Equivalent load deducted threshold < value: No action is to be carried out,
  • Equivalent charge deducted threshold > value: Urgent actions for improvements are necessary, accompanied by actions of prevention.
It should be noted that the version we are presenting here is version 2009 of the standard. It was reviewed in 2011. In its new version, it does not present a “revolution” apart from not taking into account the fact that the task is carried out by a man or a woman.

Source

1-Sumer Survey (2010) – Medical surveillance of occupational exposures

2-CNAMEs, CRAM, CGSS, INRS (2013)-Recommended Principles and practices

O. Hamon, V. Roullat (2012) – Wood trades Technology

B. Bartholomew, P. Courrège (2011) – Risk Management: Global optimization methods

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