[It Got Away] Ladder Spreaders

So I’m looking at this ladder and I’m wondering why they positioned the spreader at that exact height off the base and at that exact length.

I know that OSHA and ANSI each have lengthy manuals governing every dimension of a ladder. I figure there must be some kind of specification for those spreaders, something involving angles, geometry, maybe some trig if I’m lucky.

Maybe I’ll ask the students where they’d find the spreader on a 15-foot tall ladder and at what length. Then I’ll go find a 15-foot ladder and photograph it to verify their answer.

Or maybe we’ll develop an algorithm together, converting our intuitive sense that this ladder isn’t safe into a formula for the safe construction and placement of a spreader.

It Got Away

So I check the OSHA manual for stairways and ladders. Nothing on spreaders. Then I call Werner Ladder Co. to see if they have some kind of internal specification on the spreaders. Two days later, an engineer calls back to tell me that, nah, the spreaders are pretty much irrelevant to safe ladder usage. They only exist, this guy tells me, to guide the sides of the ladder to a specific location, at which point your body weight – not the spreader – keeps the ladder’s position fixed.

I'm Dan and this is my blog. I'm a former high school math teacher and current head of teaching at Desmos. He / him. More here.


  1. Interesting!

    I’m continually impressed that you can get these people (in industry, government, etc.) to talk to you about this stuff. Is there a trick?

  2. I think I read it on here before, but I’d guess that most of these people are happy to talk to someone about their work.

    I would guess that the ladder engineering department has gotten few (if any) calls asking something like this. They get to call someone back, talk about what they’re up to, and probably do it on company time. Win – Win situation.

  3. I love that you now have the freedom to do this kind of inquiry. It’s fascinating to hear what you get these people to tell you about their work!

    Elizabeth (aka @cheesemonkeysf on Twitter)

  4. Yeah, the hardest part is to push past the first few layers of bureaucracy – the operators and administrative assistants – and get my name and number on someone’s voicemail. The actual professionals are usually pretty thrilled to talk about their work with anybody and moreso with a teacher. You know, because there’s kids involved now.

  5. My question is this? Has anyone ever made a ladder without a spreader, and would you really feel “safe” without the legs locked in the correct position???

  6. Wow, that’s pretty interesting. There is probably some mathematics in that balancing point, though. That might be interesting to investigate.

  7. I am LOVING these inquiries that “got away.” It’s so fun to see more of your process. I’m getting a better feel for the WCYDWT process than I did from only seeing/experiencing the final products.

    Thanks for taking the time to bare this to the world :)

  8. Can I ask why you used a decimal label the height of the spreader instead of a fraction? Just thinking about how it would be measured by a student and outside of using a laser to measure the height, we’d get 9 1/4 inch (or so), right?

  9. I know in a lot of industries, a zero would be required before the decimal point. Specifically, when my daughter was having surgery this summer, her chart (and I presume every chart for every patient) had a list of “no-no”s, things that should or should no be written down.

    One was the zero in front of the decimal point. The example given was if it were a prescription, the pharmacist may fill it for 8 instead of 0.8 overdosing the patient, so the zero in front is required.

    However, a trailing zero is omitted. For example 8 vs. 8.0. Again the example given would be for the pharmacist to fill for 80 instead of 8, again overdosing the patient. I know I require my students to keep leading zeros and omit trailing zeros.

  10. @got_legos: So if there is no spreader present, is it plausible (for let’s say a 180lb person) to stand on it and have the legs remain still?

    Right. Assuming the person opened the ladder up to the OSHA specifications, her body weight would keep the ladder in place.