We have had four heartbreaking but preventable garden tractor / lawnmower accidents to children here in one week with some pretty devastating injuries. As one of the surgeons involved I have been drafted into doing radio and TV public service announcements / interviews but getting the data together is harder than I thought. I know the medical data (the statistics on the injuries sustained by children from mowers and cutters, the injury types, the long term consequences of the injuries, etc) but I cannot find the mechanical information. How fast does a lawn mower blade turn? How much energy is involved? How long does a mower blade spin after you turn of off (assuming no blade brake or even with a blade brake)? How does that energy compare to a bullet? an ax? a propeller? a _______?.... I want a comparison that will really drive home the forces involved and the dangers involved. Anybody have any ideas or suggestions on where to look for data, thoughts on what they would include or suggestions for comparisons. What am I missing? All input is welcome. The knowledge base on TBN never ceases to amaze me. Thank you in advance! -Rob
Please help with mower safety PSA
- Thread starter Surgeon
- Start date
Well, I can help with a little of it. I'm providing the details, so if I mess up a step, you or someone can jump in and fix it.
For a push mower, assume a 21" blade. Gas engines run about 3400RPM.
Figure the circumference: 3.14 x 21 / 12 (to get it to feet) = 5.495 ft
Spinning at 3400 RPM means the blade tips are moving 3400 x 5.495 = 18,683 ft/Min.
Converting to Miles/HR: 18,683 x 60 / 5,280 = 212 MPH.
If you are talking a tractor mower, like a bush hog, you would figure it the same way. The tractor PTO is probably 540 RPM on the rear, and ?? if it's a mid mower. You'd have to know or measure the gearbox ratio to figure how many RPMs the blade is turning. But the calculations are the same.
Assume a 6 ft blade with a 1:1 gear box on a rear PTO:
circumference: 6 x 3.14 = 18.84 ft
Speed: 540 x 18.84 = 10173 ft / min
MPH: 10173 x 60 / 5280 = 115 MPH.
An engineer could probably figure the energy involved when the blade hits something (I ain't one). Might be able to compare it to the impact of a bullet or an X MPH impact with a car, etc.
Oh, this would be REAL graphic, but you could video a bush hog running over a cantelop or small watermellon. I'd never want to see a person go into a mower, but my guess is it would look about the same when it happened.
Hope this helps.
Ron
For a push mower, assume a 21" blade. Gas engines run about 3400RPM.
Figure the circumference: 3.14 x 21 / 12 (to get it to feet) = 5.495 ft
Spinning at 3400 RPM means the blade tips are moving 3400 x 5.495 = 18,683 ft/Min.
Converting to Miles/HR: 18,683 x 60 / 5,280 = 212 MPH.
If you are talking a tractor mower, like a bush hog, you would figure it the same way. The tractor PTO is probably 540 RPM on the rear, and ?? if it's a mid mower. You'd have to know or measure the gearbox ratio to figure how many RPMs the blade is turning. But the calculations are the same.
Assume a 6 ft blade with a 1:1 gear box on a rear PTO:
circumference: 6 x 3.14 = 18.84 ft
Speed: 540 x 18.84 = 10173 ft / min
MPH: 10173 x 60 / 5280 = 115 MPH.
An engineer could probably figure the energy involved when the blade hits something (I ain't one). Might be able to compare it to the impact of a bullet or an X MPH impact with a car, etc.
Oh, this would be REAL graphic, but you could video a bush hog running over a cantelop or small watermellon. I'd never want to see a person go into a mower, but my guess is it would look about the same when it happened.
Hope this helps.
Ron
Last edited:
Ron, Thanks. That is a great help. I am trying to be overprepared. I have never done radio much less television. I am happy in my own little medical world but this is one of those issues that I have to crawl out of my shell and suck it up. I will ask them on Monday if they will let me run something over for the camera. -Rob
AlanB
Elite Member
The most graphic, (and sticks in my mind the absolute most) safety message I have ever seen is the one that the US Army has that says take off the ring, not the finger.
Shows the 98% severed finger, ring in the middle, end of finger off to the side.
Not sure that you would want to put something like that out, but I can tell you THAT PICTURE is why I do not wear a wedding ring.
Shows the 98% severed finger, ring in the middle, end of finger off to the side.
Not sure that you would want to put something like that out, but I can tell you THAT PICTURE is why I do not wear a wedding ring.
DrainPondDesign
Silver Member
Surgeon,
Stop trying to be nice to people, statistics and laws of physics will not change the safety habits of people who think that accidents only happen to others and that it will not happen to them because they know better.
You have what you need, show them the blood and gore, let them shake hands with a handless person or see a mutilated child, if this makes them sick so much the more memorable.
Sorry to be so blunt but as you have observed people are casual about safety until it's too late.
Good luck & go get them!
Stop trying to be nice to people, statistics and laws of physics will not change the safety habits of people who think that accidents only happen to others and that it will not happen to them because they know better.
You have what you need, show them the blood and gore, let them shake hands with a handless person or see a mutilated child, if this makes them sick so much the more memorable.
Sorry to be so blunt but as you have observed people are casual about safety until it's too late.
Good luck & go get them!
Soundguy
Old Timer
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Check most mower sales websites.. blade tip speed is listed for most of them..
Soundguy
Soundguy
AlanB
Elite Member
My memory may be faulty, or there are two of these out there.
Anyway, page 9 here.
https://crc.army.mil/MULTIMEDIA/magazines/countermeasure/2000_issues/cmmar00.pdf
I guess you have to know your audience, and what may be appropriate to one, is not to the others.
I know for me, you telling me blade tip speed of my mowers is pointless.
My buddy telling me he had a nightmare about his daughter tugging around the mower and putting her hands under it (NOTE, this did not happen, he had a dream about it) turns my stomach, and makes me thing a bit.
I think blade tip speed is OSHA regulated by the way, and should be able to find in the CFR.
Anyway, page 9 here.
https://crc.army.mil/MULTIMEDIA/magazines/countermeasure/2000_issues/cmmar00.pdf
I guess you have to know your audience, and what may be appropriate to one, is not to the others.
I know for me, you telling me blade tip speed of my mowers is pointless.
My buddy telling me he had a nightmare about his daughter tugging around the mower and putting her hands under it (NOTE, this did not happen, he had a dream about it) turns my stomach, and makes me thing a bit.
I think blade tip speed is OSHA regulated by the way, and should be able to find in the CFR.
DrainPondDesign
Silver Member
Surgeon,
Information of a more practical and socially acceptable nature.
In industry our workman's compensation insurance company often provides safety information, inspections and/or training as part of the policy cost.
You might try any large insurance company's public relations department.
Other common sources of public safety information are the police and fire departments but I've never heard of them presenting a mower hazard demonstration.
There are industrial safety training videos available for any hazard but these are copyrighted and not inexpensive.
Your idea of running a mower over a generic flesh simulant should provide an image disturbing enough for people to remember when they operate a mower with children present.
Welcome to the frustrating world of safety compliance where friends and fellow employees resist your every effort to keep them safe. Should you continue in this effort let me bestow upon you a title you are sure to be addressed by “Doctor No".
Information of a more practical and socially acceptable nature.
In industry our workman's compensation insurance company often provides safety information, inspections and/or training as part of the policy cost.
You might try any large insurance company's public relations department.
Other common sources of public safety information are the police and fire departments but I've never heard of them presenting a mower hazard demonstration.
There are industrial safety training videos available for any hazard but these are copyrighted and not inexpensive.
Your idea of running a mower over a generic flesh simulant should provide an image disturbing enough for people to remember when they operate a mower with children present.
Welcome to the frustrating world of safety compliance where friends and fellow employees resist your every effort to keep them safe. Should you continue in this effort let me bestow upon you a title you are sure to be addressed by “Doctor No".
AlanB
Elite Member
Toro / Exmark put out a safety training film as well, I think I have a copy somewhere............... But the point being more, have you contacted the mower manufacturer "Consumer safety" departments and asked for help?
It is a tough and unpopular place to be the "safety guy"
It is a tough and unpopular place to be the "safety guy"
Thanks for everyone’s help. The spot went well today. The television studio was an interesting experience (but one that I hope to avoid in the future). Given the morning audience I was nixed on any demos. (I was considering mowing a cucumber.) The numbers for these injuries are appalling. Last year alone there were 16,500 mower injuries to children and 220,000 to adults with 75 fatalities 1/5th of which were children. Radio spots next week. I will call Deere and Toro and see what they have to say.
Ron: the interviewer seemed impressed with the tip speed data.
Ron: the interviewer seemed impressed with the tip speed data.