30 August 2012
Retro-fitted seating affects integrity of steering in large earthmoving equipment
An incident involving the disconnection of the steering column of a loader has been investigated in South Australia.
It appeared that the steering column, which was located within the arm of a retro-fitted seat, became disconnected when the seat was fully raised and moved backwards to allow the driver to exit the cab (1). The steering function would have subsequently been lost from the disconnection.
1. Operator seating and the position of the steering column within the seat arm (circled).
2. The two disconnected splined steering shafts (circled) with the metal front cover of the seat arm pulled forward (to allow viewing).
3. Travel stop block (circled) in the seat guide rail fitted to prevent steering disconnection.
- The seat was designed to be retro-fitted to the loader for the ergonomic benefit of the operator.
- The seat was usually fitted with a seat tether (between the seat frame and the cab floor) by the manufacturer.
- On this occasion, it appeared that the seat was fitted by the plant owner and that the seat tether was either not fitted or not maintained
- The steering column of the loader was made up of two sections connected by a splined coupling, which allowed the column to slide freely in the seat arm to suit the ergonomic requirements of the operator.
- When the seat was adjusted to the maximum height, the two sections of the steering column apparently were on the verge of disconnection.
- When the operator stood up – and the seat rose slightly or was moved backward (or both) – sufficient additional distance developed to cause the two sections of the steering column to be completely disconnected (2) and to thereby lose steering function. The operator might not be aware of this condition as the splined coupling is hidden from normal view by the metal front cover of the seat arm.
- There was insufficient spline / coupling engagement when the seatwas raised to the maximum and / or moved back without a seat tether.
- There were no positive means to prevent the two sections of thesteering column from disconnection at the time of the incident
- Owners of load shifting plant with retro-fitted seating must ensure that the adjustable steering splined shafts forming the steering column cannot disconnect under any circumstances of use / movement of the seat.
- Where potential of disconnection of the column is identified through the process of assessment of risk, the owner must immediately contact the seat manufacturer to seek advice on the appropriate control measures to prevent disconnection without inhibiting the ergonomic benefits of the seat.
- Owners of plant must ensure that any manufacturer’s instructions are complied with including the fitting, inspection and maintenance procedures of any control devices, which have been fitted (or new ones that need to be fitted) to prevent column disconnection.
- Existing operator ‘pre-use checklists’ should be reviewed to ensure that any steering issue of this type is identified prior to use.
- After-market seating suppliers must ensure that if the seat is to be fitted to load shifting plant with a splined-type steering column, the seating design must not permit the column to be disconnected under any circumstances of seat use / operator ergonomic adjustment.
- Positive means to prevent disconnection of the column must be provided. Where possible, high level engineering controls – such as stopping blocks positioned in the seat guide rail (3) – should be used that are designed to be both integral to the seat and not to interfere with the ergonomic function of the seat. As such, seat tethers (connecting seat frame to the cab floor) should only be used where fitting a guide rail stopping block (or other higher level engineering control) is not reasonably practicable. If a seat tether is used, disconnection of the splined-type steering column must not be possible.
- Information on any control measures fitted to prevent column disconnection relating to installing, inspecting or maintaining the seating / steering integrity must be passed on to the plant owner. This should include any recommended checks to perform on the control(s) for inclusion in the user’s ‘pre - use checklist’ for the vehicle.
- Other administrative controls – such as warning signs – should only be used in conjunction with the other higher level engineering and administrative controls listed above.
For further information on this safety alert please contact: Dr. Ian James Ellison, Executive Officer, MAQOHSC