Many standards assume a weight of 75 kg for human beings, for example for the formulation of test methods or requirements to be met by products. However, a study by KAN has revealed a need for standards and EU legislation to be amended in this respect.
Have you ever noticed the sign in a lift showing the permissible total weight of its occupants, and worked out just how much, on average, an occupant of the lift is allowed to weigh? The answer is often 75 kg. But seriously, what do you think the average person weighs? Your guess would probably be: more than 75 kg. In the lift, this isn’t an issue: if the permissible combined weight of the occupants is exceeded, the doors don’t close and the lift stays put.
It becomes an issue for occupational safety and health however when products intended to carry or restrain people are designed based upon an assumed weight of the intended users and this weight is too low. In some cases, the maximum permissible weight is simply not apparent. Should the weight specified in the standards or the intended tests be 75 kg, the resulting products may present a hazard when used by persons whose weight exceeds this figure. Ambulances are a good example. The anchor points for the stretcher are tested for the weight of the stretcher and a test dummy with a weight of 75 kg lying on it. Should an accident occur and the patient weigh significantly more than 75 kg, an additional safety risk may arise if the anchor point fails as a result.
Many products exist that are required to bear or transport human beings. They include couches, stretchers, seats of various kinds, skateboards, floatation devices, medical devices, fire ladders and fall protection equipment, to name just a few. Anthropometric data obtained in recent scientific studies show that a human body weight of 75 kg no longer reflects the reality. In a statement issued at the request of KAN, the German Federal Institute for Occupational Safety and Health (BAuA) has stated that the weights in standards should be defined with reference to generic ergonomics standards. Accordingly, the 99th percentile should serve as a basis for applications relevant to safety (refer to the information box below). It is also advantageous for products to be planned such that they can be used by as many people as possible.
For defining user’s weights in standards and legislation, the BAuA therefore recommends that data from studies representative of the entire German population be used. A study of the health of adults in Germany, conducted in 2012, indicated the following weights for the human body: the 99th percentile corresponds to a body weight of 129.1 kg for men and 119.1 kg for women. The study examined around 3,000 persons of each sex, which cannot be considered representative of the entire German, much less European population. ISO 7250-3 however states 99th percentiles of 142 kg and 119 kg for men and women respectively in Europe. There is therefore much to suggest that a figure much higher than 75 kg should be used.
To enable the issue to be analysed in greater detail, KAN tasked DIN Software GmbH at the end of 2019 with surveying standards and European legislation for references to the weight of persons. Full-text searches were performed for terms concerning persons or test dummies in conjunction with statements of weight.
Analysis of the results showed 75 kg to be the value most frequently stated for the weight of a human being in standards and European regulations. The figure of 75 kg is stated in around 100 documents; in fact, over 50 documents state a figure below 75 kg. Documents stating much higher values were also identified, however: overall, the values stated for the weight of a human being range from 50 to 360 kg (see Figure 1). Key topics are the areas of mechanical engineering and sports, European directives and regulations, and UNECE regulations (see Figure 2).
Can the problem be resolved simply by replacement of the value in the standards with a different value? Unfortunately, the issue is not quite so simple. Applications exist for example for which the relevant value is not the highest assumed value. These include applications in which a triggering threshold must also be stated for low weights. This is the case for instance for seat suspension, or for a pressure sensor that switches off a machine when stepped on. The question also remains as to which value is the “right” value. The results of the survey are being discussed initially within KAN. The intention is for recommendations to be formulated for standardization activity, and also for influence to be exerted upon EU legislation (for example in the automotive sector), as this often serves as the basis for standards. The aim is for realistic values to be found for human body weights which correspond to up-to-date anthropometric data and which can be incorporated into the documents.
Katharina von Rymon Lipinski