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I've just bought myself an electrical chainsaw. Specifications of the chain velocity of my saw read 55 km/hr.

I've read online that many wood-cutters have encountered chain breaks and want to protect myself against unfortunate accidents.

So, my idea is to always cut with the underside of the blade. This way if a break occurs at the point of contact with the wood and since the direction of motion of the chain is towards me from the underside, the chain will move away from me when it snaps. I am basing this on the fact that the saw has a small sprocket underneath giving motion to the chain. When it breaks the sprocket cannot pull it towards me anymore and given the momentum of the other outward sprocket on the head of the blade, the chain will be pulled outwards, up and away from me. All this supposing that I am always cutting with the underside of the blade.

I do not know if I am correct though! Do you know of any experiments that have been conducted to demonstrate this? Since this is a matter of life and death, I would expect much information about this, but I can't find any!

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    $\begingroup$ The most dangerous tools are ones you don't know how to use, are scared of, or have a dull blade. Solar Mike's answer is the best solution, but basically if you are aware of the dangers involved and basic safety measures chainsaws aren't anymore dangerous than any other woodworking power tool. $\endgroup$
    – jko
    Aug 24, 2020 at 11:42
  • $\begingroup$ @jko, chain saws are clearly more dangerous than circular saws or power drills. You can mitigate the danger, but the safest way to use a chain saw is to not. $\endgroup$
    – Tiger Guy
    Aug 26, 2020 at 8:59
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    $\begingroup$ Please do not vandalize your own posts. I rolled back to the previous version such that the existing answers match the question. $\endgroup$
    – OpticalResonator
    Nov 13, 2020 at 16:40

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Another perspective : A friend retired as a manager with a large lumber company ( Louisiana Pacific ). He had spent much of his career overseeing cutting crews. They did not try to figure out when or how a chain might break , he just wore a heavy leather apron whenever he used a chainsaw . I understand his crews also used the aprons. We had a volunteer group that helped clear downed trees on the TX coast after storms. He pretty much did all the chainsaw work.

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Best solution is:

  1. have and use the proper safety gear including the trousers (these are designed to catch the chain before they get to your skin and they work), helmet with face shield and safety boots.

  2. maintain bar, chain and sprockets correctly. I have used chainsaws for the last 40 years and at one time I have 4 of various sizes. I also sharpen my chains and they cut fine until they are worn out, BUT I have never had a chain break as I make sure that the lubrication is there and watch where the bar is when cutting.

As for only using the bottom of the bar for cutting, I rotate the bar when I swap chains as I use two chains concurrently, also I have cut with the top edge, bottom edge and point of the bar - how else do you start a plunge cut...

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    $\begingroup$ @dimachaerus preventative maintenance probably wins... And knowing how to use it properly. $\endgroup$
    – Solar Mike
    Aug 24, 2020 at 12:32
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    $\begingroup$ @dimachaerus statistically kickback is a more likely issue than the chain snapping. In the US every year for every 100 chainsaws sold there is less than 1 injury. If you're using the saw correctly (cutting with the proper edge) and stay out of the plane of the bar, you'll be fine. $\endgroup$
    – jko
    Aug 24, 2020 at 12:41
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    $\begingroup$ @dimachaerus "[...] that's not what I asked." Isn't it, though? You asked how to prevent injury from the chain snapping and Solar Mike told you to properly maintain it and wear protective gear, sounds like a pretty solid answer. Statistically, there is always a risk left, but then again, you want to use a chainsaw. $\endgroup$
    – OpticalResonator
    Aug 24, 2020 at 14:31
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    $\begingroup$ @jko 1 in 100 is a pretty high chance of an accident. $\endgroup$
    – user253751
    Aug 25, 2020 at 10:27
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    $\begingroup$ @user253751 that's 1 accident/year per 100 sold that year. Assuming people use a chainsaw longer than a year before buying another, it's much lower than 1 in 100. I would assume most of those are with professional arborists using a saw everyday, not a weekend warrior using it a few times a year. $\endgroup$
    – jko
    Aug 25, 2020 at 12:11
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  1. Chain breaks are a very low risk factor compared to many others risk factors.

  2. I've worked as a full time hazard cutter for the USFS, and I've never seen one break. If they do break, you can be nearly certain that it was damaged long before it broke. Don't let the bar/chain get pinched. If it gets pinched badly - toss it. Don't pull on a pinched saw, roll the log with a peavey, jack or lever the log, or saw your way out with another saw. Always run the chain over the bar a full round before starting the saw. Any kink or hiccup in the chain's travel means it's time to toss the chain.

  3. Stuff wears out on a saw. Crappy little homeowner saws are often garbage after about 50 hours. That's their design life. Commercial saws last long enough that you will replace bars and chains before the engine or drive dies.

  4. It is possible to break a chain. You could cut into a railroad spike buried deep in the wood. People used to spike trees to prevent a stand from getting logged. But normally, that just tears some teeth off.

  5. Learn to sharpen a chain by hand, and do it often. This makes you handle every link in the chain, and you will find damaged chains that way. Store chains unkinked and handle them with care.

  6. Take a sawyers course from an OSHA or FISTA certified instructor. The USFS and many fire depts. offer courses.

  7. So worry about the condition of the chain when the saw is off. Forget about it when sawing, there is plenty of more important stuff to think about then.

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When it breaks the sprocket cannot pull it towards me anymore and given the momentum of the other outward sprocket on the head of the blade, the chain will be pulled outwards, up and away from me. All this supposing that I am always cutting with the underside of the blade. I do not know if I am correct though! Do you know of any experiments that have been conducted to demonstrate this?

I didn't find experiments with cursory googling either, which is not saying there are none. Kickback accidents appear to be far more common than broken chains. If the purpose of your question is safety, it is misguided: Even with experiment, we could only prove that you are wrong (when the broken chain hits the dummy in the face or so). The tension in the chain together with the piece you are working on could fling a broken chain any which way. No experiment can prove that you are safe from a broken chain. Just wear PPE.

Your basic reasoning about what should happen is sound, but neglects the tension in the chain and possible interactions with the wood being worked on - say the chain hits a nail in a flexible tree branch. then again, helmets with face shields start at 20 € so I'd just get one of those and be done with it.

If you just want to make sure your hunch about what happens if a chain breaks, your question is valid and I too was surprised youtube isnt filled with relevant videos (though I didn't search extensivly, my lunch break is coming up).

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    $\begingroup$ Cutting with the top of the chain is a normal part of bucking logs. With no slot for the chain to come out of, it is safe, and some operations, such as fire/rescue first responders, are taught to saw upwards any time they can. This doesn't apply to little pruning saws or pole saws, though. $\endgroup$
    – Phil Sweet
    Aug 25, 2020 at 23:58

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