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The TLVs are tables showing stress limit values beyond which the work presents significant risks of MSD. There are tables for carrying loads and manual operations.

## Introduction

The ACGIH (American Conference of Governmental Industrial Hygienists) is an American organization founded in 1938 in charge of developing guidelines on safety, hygiene and environmental issues.

These guidelines allow, on the basis of certain evaluation criteria, to define limits (weight…) beyond which there are significant risks of injury.

## TLV for manual activities

The first tool is used to evaluate manual activities. Is understood as a manual activity when:

• The rated manual work is done for 4 hours or more per day.
• A single task is repeated X times over the working time.
• The movements of the hands and handles are evaluated only.

It should be noted that the use of this tool requires some judgemental expertise. It is not considered the problems related to the posture, the vibrations… and therefore it is necessary to know how to weight them tacitly during the evaluation.

### Step 1 – Observing the activity

The first step in the method is to observe the movement carried out by the operator. For this, the best is to make a video of the activity. The use of the video will allow to evaluate the same situation to several, key point for the quality of this evaluation.

It should be noted that the assessment of the left hand and the right hand is done separately.

### Step 2 – Evaluate the maximum force

The maximum force is expressed as 90% of the worker’s efforts throughout his working day with his fingers. by finger, it is understood the efforts applied by the wrist, the hand and the forearm.

Here it is opposite the term of the maximum to the average force. An average effort above 15% of the maximum force will not be held in an extended manner. And, considering an average effort masks the peaks of effort.

The evaluation takes place on a scale of 1 to 10.

### Step 3-Evaluating the activity

The term ” hand Activity Level ” is often used, which refers to repeated and continuous movements and efforts of hands during work.

Its evaluation takes into account the frequency at which the hands carry out the movement and the work cycle (the ratio between the action time and the pause time).

The evaluation is carried out according to 2 methods:

• On a scale of 0 to 10, 0 being a work requiring no movement and effortless, 10 being a continuous work, fast and requiring strength.
• Via a calculation involving the frequency of the movement and the pause time (see table to download).

### Step 4-Interpret the score

Once the assessment has been made of the two previous factors, we refer to the following graph.

Depending on the position of our situation, actions are to be taken with regard to the following table:

## The TLV for the load port

The second tool is to evaluate the maximum weight to be carried in relation to the work situation. This simple method does not apply in the following cases or at least the limit values will have to be reviewed downward:

• Binding posture: kneeling, seated…
• Lifting a load with one hand
• Binding medium: cold, humidity…
• Bad grip on the object to be raised
• Presses the unstable ground

### Step 1 – Identify the frequency

The first step is to measure the frequency at which the carrying motion of a load is carried out. It will be identified according to the time per day allotted to the task and the frequency of movement over that time period.

### Step 2 – Identify the maximum value

Depending on the previous result, we will choose the table best suited to our situation. These tables allow us to cross-

• The vertical position at the beginning of the movement
• The horizontal position

Depending on these 2 parameters, we will identify the maximum weight to be made by the element to be raised. Weight beyond which, the work situation presents a significant risk of MSD and injuries.