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Jonathan King: Finding a safer solution

Logging core is bread and butter work for a geologist and to carry this out each PVC core barrel liner tube has to be split with two handmade cuts but how often is the safety of this approach considered?

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Jonathan King is an independent engineering geologist

A hooked blade Stanley knife is often used by logging engineers, geologists and drillers both in the field and laboratory to undertake this task. Dragging a razor-sharp blade through 1mm thick PVC that may be old and locally brittle, or when the knife point snags a quartz vein, means the blade can break free of the liner in an uncontrolled sweep that is capable of slicing through drillers gloves and causing a serious flesh wound. Since slashing my hand this way, I have found that many others have had the same experience and opening liner tubes is considered one of the more high-risk aspects of geological sampling.

To quote the Health and Safety Executive, “knife injuries to hands often happen when the knife slips during cutting or trimming. In most cases the blade comes into contact with the worker’s other hand, causing a laceration to the hand and/or fingers. Injuries can also occur to other parts of the body, including the knife hand itself”.

Since my injury I have approached opening liners with trepidation and great caution. It has also led me to seek a safer, more controlled way to do it.

I tried a lever system to pull the knife through like a come-along winch, but had difficulty developing a fulcrum firm enough. I also experimented with an angle grinder with a concrete blade but fumes from melted plastic stopped that. An oscillating multitool with a saw blade was very safe and effective but slow.



A Stanley 1995H blade only protrudes some 5mm to 10mm beyond the tool boss – giving little opportunity for an accidental cut – and the second, back blade can be easily masked with heavy tape.

Then I tried bolting a hooked Stanley knife blade directly onto the mulititool. A soft plastic washer is needed to mount it against the locator pins as without that the blade shattered when tightened against the pins. When the oscillating blade was pulled along the liner, it slid through the PVC with little resistance requiring less strength to pull and minimal uncontrolled movement if the blade broke free resulting in opening the sample in a safer, more controlled way.

If a Stanley 1995H blade is used it only protrudes some 5mm to 10mm beyond the tool boss – giving little opportunity for an accidental cut – and the second, back blade can be easily masked with heavy tape. Standard commercial hooked multitool carpet blades are available but, as they are longer than the Stanley blade, they protrude some 50mm and vibrate more, catch on quartz more easily and are less controllable they are not ideal. They also have external sharp surfaces which is an additional health and safety issue.

When mounted to a battery multitool, the modified oscillating knife can be used in the field and wider use of the solution could significantly reduce the risk of hand knife injuries while carrying out the common geological task of opening core liners.

The solution to the problem is simple and it begs the question, what other every day work risks do we just accept rather than looking for a safer alternative?

  • Jonathan King is an independent engineering geologist


Readers' comments (4)

  • a picture of the blade and in the tool would be good

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  • I would recommend that you try the 'core cutter' available from Stuart Well Services. This is a sturdy hand tool with a rounded off hooked blade to prevent stabbing or cutting injury.

    Also, anyone using multitools should consider their exposure to excessive vibration. It is surprising how quickly a recommended daily limit can be achieved with some of the more powerful tools out there.

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  • A picture of the blade has now been added.

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  • The Stewart core cutter looks well designed to reduce or eliminate stabbing or cutting but I would think still needs significant strength to make the initial puncture and then hold it against the liner to make the cut. An advantage of the oscillating hooked knife is the ease with which it cuts allowing more control which may prove a useful alternative, especially for those with less arm strength.

    The vibration issue depends upon the multitool used. Reported vibration levels I have seen vary from 3 to 16 m/s2 with the lower value not a problem for up to 2 hours daily use. Also the small mass and lever arm of the hooked blade provide little momentum hence little vibration of the tool.

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