Liberty Mutual Research Centre 1994-5 Visiting Scholar Study
Dr Ted Lovesey
In the tradition of Liberty Mutual, claims for injury indicated that vibration of the working environment might be causing severe musculo skeletal disorders in the transport workforce. This needed to be investigated.
Decades earlier, by a somewhat serendipitous process, I had been drawn into the study of the effects of multi-axis vibration upon human performance and comfort. This involved shaking the UK Concords Test Pilots in a 5 axis vibration simulator to evaluate if they would be troubled by vibration caused at take off from a particularly bad European runway. (They were not, but Test Pilots can cope with almost anything).
With this background, I was invited to investigate and establish the size of the vibration problem. Before this G Sorrock had conducted an initial search of 672 claims for 1993 and found 171 which might be linked to vibration or shock.
I arranged for a further much larger study in which the Workers Compensation data base from 1989-1993 was used to look for the 9 key words of jolt, jar, shock, vibration, impact, knock, bounce, bump and bang were used. This covered driver categories from truck and postal drivers to chauffeurs. It produced 10,659 records which contained one line descriptions of the accident or injury where these words were used. Analysis of the descriptions showed that many accidents and injuries were due to the drivers jumping down from the cab, lifting goods or hitting potholes. Care had to be applied to interpreting the data as many shocks were due to electrical equipment.
A classic case of jar was when one driver dropped a glass jar on his foot!
Beware of blindly accepting what the computer says.
Some vibration induced injuries really were a problem when anti-vibration seats were badly adjusted or broken due to lack of maintenance.
Despite these initial indications it was decided to examine all aspects which might indicate hidden, but potentially correctable, problems.
Perhaps the largest effort was spent in fitting the Centers’ International Tractor cab with 3-axis accelerometers mounted on the floor and on the driver seat cushion. These measured the vibration into the driver and passenger/observer. The driver’s statures were measured to 1mm before and after each 3 one hour long drive around a defined measured route. Despite the rough ride no significance difference in stature was found throughout the day. The anti-vibration seat gave a better ride subjectively than the passenger seat despite amplifying 2Hz vertical vibration. Video recording of the driver was taken during each 1 hour long run to add to the passengers notes.
The cab geometry including available adjustments to seat, steering column, etc were also measured as it was thought that seating posture was probably an equally important factor. The areas used in this study are shown in the accompanying figure.
Unlike most other vehicle whole body vibration studies elsewhere, the LMRC for Safety and Health program took a comprehensive view of all primary factors which might contribute to driver health problems.
Although short duration high amplitude motion such as hitting a pothole was a cause of concern (i.e. not vibration) it was concluded that vibration was not a significant problem apart from causing fatigue as do other environmental problems such as noise, etc. Posture, manual handling of stores, psychological pressure of work schedules are probably of greater importance.
Most of these were being addressed elsewhere in the LMRC.
Dr Ted Lovesey
Stoke Gabriel, UK 1st November 2017