wondering about liability

[lockmanslammin]

I was just wondering if anyone else worries about the liability involved personally, when giving people advice on how to build a good cannon? I have been trying to give someone advice recently (on the forum) and although I feel that I have plainly stated the safety issues I see, at the same time I give performance upgrade advice.
Am I just being a worry wort, or have others thought about this?

Chris

[jrrdw]

I think it's safe to say some kind of safety issue crosses everyone's mind at some point in time but at the end of the day you can't hold everyone's hand making sure they are doing things to the utmost safety standards.

Liability is on the user!

[mark.f]

I don't worry about liability as much as I used to.

First off, I'm confident in my own advice (especially safety-related), and secondly, we have literally hundreds of people actively reading most threads who won't hesitate to correct another person if they give unsafe/bad advice.

If anything, worry about the liability of running your own website. PCGUY probably sweats it a lot more than you would have reason to...

[D_Hall]

First off, I'm confident in my own advice (especially safety-related), and secondly, we have literally hundreds of people actively reading most threads who won't hesitate to correct another person if they give unsafe/bad advice.

And yet, PVC is the building material of choice around here.... In other words, literally hundreds of people can give bad advice.

[lockmanslammin]

I'm guessing it isn't to difficult to know what thread I'm really talking about that I'm currently helping some on out in. I just worry too much I guess. It's just that no one else has commented on the thread at all. It made me feel like I was the guys only source of info on how not to injure himself. Which is untrue in a way I guess as HE is also an important party involving his safety. What do you guys generally feel is a safe working pressure for 1 1/4" sch. 40 pvc anyhow?
Chris

[mark.f]

And yet, PVC is the building material of choice around here.... In other words, literally hundreds of people can have an opinion.

Fixed that for you.

[jimmy101]

And yet, PVC is the building material of choice around here.... In other words, literally hundreds of people can give bad advice.

What is wrong with PVC being the material of choice? If it is up to the task (pressure rated pipe in a 1x combustion) then it isn't bad advice.

[D_Hall]

And yet, PVC is the building material of choice around here.... In other words, literally hundreds of people can give bad advice.

What is wrong with PVC being the material of choice? If it is up to the task (pressure rated pipe in a 1x combustion) then it isn't bad advice.

It's pressure rated for liquids, not for gases. Failure mechanics of it suck. It's prone to microfractures due to mishandling. It's just a Bad Choice.

But it's cheap and works most of the time so nobody cares about actual engineering practices.

[dart guy]

Well it's not like anyone on here is going to sue someone for some helpful advice. If you build the thing it's your responsibility if you screwed up, I personally liked the idea of " it's your own stupid fault" rather than random suing other things. It's kinda like you accept the danger if you actually build the cannon.

[jimmy101]

It's pressure rated for liquids, not for gases.

But failure is pressure, and not medium, dependent. It is no more likely to fail when pressurized with a gas than it is when pressurized with a liquid.

Failure mechanics of it suck.

True, but most materials have crappy failure mechanics when they are pressurized with a gas. Given the higher sectional density of metal fragments a failure in a metal container is going to generate fragments that are more dangerous than the fairly low sectional density fragments from plastics.

It's prone to micro-fractures due to mishandling.

True but nearly all materials have problems with "mishandling".

It's just a Bad Choice.

My house has a hundred feet or so of PVC pipe that is often pressurized to 100 PSIG with water. The system is 100% to building and material specs. I don't think that would be considered a "bad choice". It is a choice but so is every other time you choose a material to make something.

But it's cheap and works most of the time so nobody cares about actual engineering practices.

What engineering practices apply to launching 50g chunks of spud out of a homemade cannon? Besides, "engineering practices" aren't written in stone. The cost, end use and potential for injury all figure into "engineering practices" decisions. Sometimes "engineering practice" is a 10x safety margin. Other times it is a 10% safety margin. There is no universal definition of "engineering practice", there are just practices commonly used for particular situations. If a group of engineers ever get together and come up with a science based spec for spud guns I would happily follow those guidelines.

"Engineering practices" have a fair amount of "build it and see if it fails" in it. Current codes and standards are more often set by bad experiences than by clear foresight into the mechanics and causes of failures. The World Trade Center and Fukishima power plants were built using the best "engineering standards". They failed spectacularly. The "engineering practices" are now being changed to keep the same failures from happening again.