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Ergonomics General Notes

This page provides a few general guidance notee relating to the information provided on this site and its relevance to mechanical engineers

Introduction

This website contains various values and dimension obtained from a variety of sources relating to ergonomics or human factors - the relationship between man and machines.   I have tried to provide links which include better quality information and in the reference book section of this site I have identified books which are useful.  If the information you seek is important please use these sources of information.

Engineers are responsible for the safety of those using the equipment they design, make or maintain and and should reference the relevant regulations

It must be stressed that man comes in so many variations that it is not possible to provide set values for sizes and strengths of men to be used for the design of equipment and access spaces.  A individual person starts as a child and ends as a old person and within that period can be fat or thin, strong or weak, well or ill.  Throughout the world there is significant variation in the normal strength and sizes of individuals.

In designing equipment it is desirable that the majority of relevant indivuals should be able to operate the controls and the equipment should be strong enough and large enough to withstand and support the biggest, strongest and heaviest persons.  Equipment should be specified for the weakest,the strongest, smallest, the largest users.

Statistics

When looking at a range of strengths and sizes individuals it is necessary to use statistics.   The individuals are assumed to be distributed in a normal distribution.   In a normal distribution all three statistics, the mean, median, and mode are the same.

The confidence interval of a normal distribution is the middle percentage of the total population.   A CI of 95% of a population excludes the bottom 2.5% and the top 2.5% of the collection.   The confidence interval of a population may be obtained from the mean and the SD using the following:

 Confidence interval 66% = Mean +/- 1.SD Confidence interval 90% = Mean +/- 1,65.SD Confidence interval 95% = Mean +/- 1,95.SD

Example:
In a population the mean = 50 and the SD = 5
Therefore 45-55 ( 50 +/- 5) include = 66% of the population.