DES Access Mechanisms – examples of Table 12.1

Table 12.1 is a listing of possible mechanisms for whole body or part body access into the damaging energy space of an energy source external to the human body.

Here are a few examples from my experience (over the years I have known of and forgotten the details of many others) of some of the mechanisms.  All of them except one involves powered machinery as an energy source.

1. Inadvertent movement into the DES

  1. In a steel mill water was used to cool molten metal that had been cast into billets.  The highly heated water drained away through a series of open channels and into a cooling tank.  The nature of the process was that the water carried with it fine particles and periodically the channels had to be manually cleaned of the deposits of this fine material.  One evening, while engaged in this cleaning work and with the channels partially obscured by steam, a man lost his footing (stumbled or slipped) and fell into one of the channels, receiving severe burns from which he later died.
  2. An operator of a machine had to stand on a platform that moved with the machine.  The platform slid over a fixed base plate, but the detailed design was such that there was an unprotected opening between moving and fixed plates.  One day his foot happened to be over the edge of the moving plate and got caught between it and the fixed plate, leading to an amputation.

2.  Purposeful action into the DES

  1.  The operator of a milk carton filling machine had become accustomed to clearing jammed cartons from the filling area by reaching in quickly to flick the carton out at a particular point in the automated process.  This was achieved by disabling the interlocked guard that was intended to prevent access while the machine operated.  His motivation was avoidance of the large amount of overtime that would otherwise need to be worked each day to make up for the lost production if the machine was stopped by the interlock each time a jam occurred.
  2. Access between the stands of a five-stand rolling mill in a steel coil rolling plant was achieved by opening a small gate.  Operators were expected to use the 415V isolator arm next to the gate to isolate the energy sources of the machine prior to entry.  On many occasions they did not do this, assuming they understood in which part of the cycle the machine was currently operating.  An operator entered the space between the rolls without using the isolator arm.  While there between the rolls doing whatever it was he thought necessary, the mill operated and the leading edge of the roll coming through the mill caught the operator pushing him into the next stand of powered rollers and killing him.

3.  DES energised while the DES is occupied

  1.  A fitter had his head inside the jaws of a blow moulding machine in order to replace a circuit board in the machine’s controller.  Having replaced the board, the machine operated and the jaws began to close.  He reacted rapidly and extracted his head just in time to avoid almost certain death.  I was told his hair turned white in the couple of weeks following the experience.
  2. An operator of a paper roll docking machine opened the interlocked guard of the docker (used to cut long rolls into toilet roll lengths) to remove a blockage.  As he did so, the arm holding the rotating blade used for this purpose continued the remainder of its cycle, slicing through the space between his second and third fingers and into the back of his hand.
  3. A steel sheet docking machine made use of a cutting device mounted on a carriage that pulled it across the width of the sheet being docked to length.  The carriage became dislodged from its tracks and a fitter was called in to return the machine to production.  This task required the fitter to stand inside the overall frame of the machine.  When the docker was replaced on its rails it immediately continued with its cycle and travelled rapidly towards the fitter, crushing his chest and killing him.
  4. Two men were sitting on a beam adjacent to the movement area of a large mechanism that involved travelling steel frames.  While in this position, the frames unexpectedly began to move and the men had to scramble rapidly to get their lower legs out of the trapping space.

4.  Entangled with and possibly pulled into the DES

  1.  An operator was standing on the counter-rotating chipper of a wood chipping machine, I think in order to access some other part of the equipment that needed some attention, perhaps for cleaning.  The machine had been stopped for various works to be completed.  The equipment was started from some remote location and the chipper mill wheels grabbed one of his boots and pulled it in between the rollers, chipping away at it and his feet as it did so.  I was told the machine was stopped in response to his yells.  He lost a sizeable part of one foot.
  2. A cleaner was shovelling spillage from around an operating take-up pulley on a bulk material belt conveyor system. He was found dead next to the pulley, with his arm torn off.  It was assumed, based on the circumstances, that his shovel had become entangled between the pulley and the belt, dragging his arm into the in-running nip point.
  3. A worker in a mine was employed in the operation of the belt conveyor system used to remove mined material to the stockpile.  One day he was reported missing by his family to the police and the mine operators but was never found.  Some time later, a shoe and other belongings were found next to a remote part of the conveyor system and the mine operators wondered whether he had been sleeping on the belt at this point (apparently it was known this did at times happen and this was the most suitable location being a seldom visited part of the system) and been dragged between the belt and the nearby pulley, losing one shoe in the process.

5.  Caught by an unanticipated movement of a machine part outside its apparent operating boundary

This is the one mechanism of which I have never had experience.  I wonder if this is due to the attention paid to the proper engineering of exclusion controls?

Leave a Comment