Two pieces of 2x4 ejected by edger into a wall more than 20 metres away

Monday, December 03, 2007

Fall/Winter 2007

What happened?

While a sawmill line was in full production, a trimmer operator saw two pieces of 16-foot (5-metre) 2x4 fly out of the edger saw outfeed at great speed and become embedded in a wall approximately 23 metres (70 feet) away at a height of about 2.5 metres (8 feet). No one was injured.

Why did it happen?

The edger was equipped with a hood-type guard at the outfeed to catch any pieces that might be ejected. The distance between the outfeed and the guard was about 6 metres (20 feet). The boards were ejected about

60 centimetres (two feet) above the top of the guard because of the “finger tailer” that moves up and down to separate good lumber from the slabs.

The rotating speed of the edger saw is 3,600 rpm and the normal travelling speed of the board as it’s processed by the edger is 6.4 metres (21 feet) per second. Four press rollers hold the board as it goes through the edger. It appears that the rollers were not able to hold the board down in this incident, causing the rotating saws to propel the two pieces of 2x4 out of the edger at a great speed.

How can it be prevented?

A thorough inspection of the edger outfeed by two millwrights and the sawmill superintendent found no major abnormalities aside from the loose bedroll in one of the four press rollers. This meant there was a good chance that the incident could happen again, propelling wood through the air at lethal speeds.

The lesson learned from the incident is that an effective guard needs to protect workers from exceptional circumstances such as minor technical breakdowns, rather than just the consequences of normal operation.

The day after the incident, a deflector guard was installed to prevent pieces of board from being ejected above the outfeed guard. The outfeed guard was also lengthened to prevent wood from flying past it.

Effective hazard recognition, assessment and control involve breaking down all the steps of a job or process to pinpoint all hazards, not just the obvious ones. The four most common equipment-related hazards to look

for are:

  • inadequate guarding or barriers;
  • defective tools and equipment;
  • incorrect tools and equipment for the job;
  • inadequate warning systems.