This video was recently passed on to DrillSafe and very dramatically demonstrates why longstroke top drive drill rigs should not be used in diamond core drilling operations.
Watch the video in full screen mode to see the details and the lead up to the failure.
Description of the accident
The details surrounding this accident are unclear and so the comments included here are based on our interpretation of what we can see in the video.
The drill is a longstroke top drive which means that there are multiple connections in the quill rod. The connections of thin walled diamond drill rod are much weaker than the mid-body of the drill rod and so each is a potential point of fatigue failure.
In the video, it appears that the drillstring is rotating but then begins to torque up. The rotation head is then moved down quite a distance and very quickly which suggests that the driller had the rig in fast travel mode (rod tripping mode). Fast travel allows the main hydraulic cylinder to apply a much greater load than when in fine feed (drilling) mode. The extreme thrust on the drillstring caused the quill to bend beyond its elastic limit and amazingly cause two connection to fail simultaneously.
It is unclear what the driller was doing at the time of the accident but the presence of the helper on the rig floor and the drill rods on the rod rack suggest that he was running into the hole and reaming at the same time. The helper would have been there to help add a new drill rod.
Lessons to be learnt from this accident
If longstroke top drives are used in diamond core drilling operations we must ensure that they are only used with a 3 metre quill rod. This in turn, means that the contractor must drill with a 3 metre core barrel or, if he uses a 6 metre corebarrel, he will have to add a new 3 metre quill rod once he has advanced the first 3 metres.
On this drill rig the control panel is "remote" and so the driller is out of the line of fire, the helper however was in the line of fire. The no-go area around the drill rig when the drillstring is rotating must be respected at all times. We strongly believe that all drill rigs should be remotely controlled - either through a wireless connection to the drill or through a hard wired connection.
The rotation guard fitted to the base of the feed frame was pretty useless in this incident. Most manufacturers fit similar guards to their drills but they only act to inhibit someone making contact with the rotation head - they cannot prevent a failed quill rod impacting the driller or a member of the crew. We must not be tempted to build further guards around the feed frame - I believe that to remove the driller through a remote control function would be a far more effective control.