Visibility requirements for the driver's stand of lift trucks: Experimental study of drivers' lateral head movements

Every year, lift trucks are involved in 9000 occupational accidents with stoppage of work. Most of those accidents are due to insufficient visibility from the driver's stand of lift trucks. Draft standards related to this characteristics take into account sideways head movements of from 300 to 600 mm, depending on the proposal. Continuous recording of movements was carried out on eight subjects in a test situation involving loading, unloading and driving the vehicle loaded and unloaded. On average, during 92% of the time driving the vehicle unloaded and 87% of time driving the vehicle loaded, the head is displaced less than 150 mm. Extreme positions are the least utilised: there is a gaussian distribution of movements around the central position. Movements accepted in draft standards are therefore overestimated. These experiments offer a partial interpretation of the differences of mobility observed between each of the four tasks.