• #1
jack action
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There are often questions on Physics Forums related to building machines or structures that are left unanswered because of this guideline (found in the Physics Forums Global Guidelines):
Legal and Health Implications:
Physics Forums reserves the right to remove and block discussion where there is plausibility that discussion may lead to litigation or affect ones health.
But all one wants to know is how much weight a beam can support or something similar. Surely, there are formulas for this?
There are. But the known equations give the maximum value that the beam can possibly hold. In other words, if you get 1000 N as an answer, it means that it will surely be impossible to exceed that limit … but the value could be less if things are not perfect. And they never are.
How much less? This is where the concept of the safety factor is introduced...

Continue reading...


 
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Answers and Replies

  • #2
hutchphd
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Nice concise statement of the issues. I am always worried about the process of providing numbers or formulae that should be easy for even marginally competent folks to obtain. Just tell them where to look.
I am also reminded of making an off-hand remark (early in my PF experience) about making a spot welder using a certain discarded kitchen appliance. This was expertly intercepted in about five minutes by vigilant staff who mentioned this was never a good idea to talk about. After a moment's consideration I said "duh"!
 
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  • #3
anorlunda
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I see your point Jack. Good for you. But for the record, I've never used that guideline about litigation. Instead, I referred to the following guideline.

Illegal & Dangerous Activities:
Explicit "how to" discussions of illegal and/or dangerous activities, or posts advocating such activities, are prohibited; such as: how to make explosives, manufacture crack, steal software, hack into the CIA, ...

Often missed is that the guideline depends on the topic, not the qualifications of the poster. DIY buildings are like DIY explosives; categorically dangerous. DIY buildings that ignore local codes and permit requirements are also illegal.
 
  • #4
jack action
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DIY buildings are like DIY explosives; categorically dangerous. DIY buildings that ignore local codes and permit requirements are also illegal.
I disagree. You may not want to discuss explosives because of readers with bad intentions. And I know of very few (none?) DIY applications for explosives. If the local laws say DIYers can do it themselves, I don't see any problem.

But then the first question to the OP is probably: «What does the local code say?» If the OP can't answer, send him back to do his homework. If he doesn't understand something in the code, or is wondering why it is required, then the discussion can go on.

I think PF could be helpful in this manner by showing the proper way and guide towards the proper resources.
 
  • #5
berkeman
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I disagree. You may not want to discuss explosives because of readers with bad intentions. And I know of very few (none?) DIY applications for explosives. If the local laws say DIYers can do it themselves, I don't see any problem.
I think PF could be helpful in this manner by showing the proper way and guide towards the proper resources.
No, as a Medic and an EE who almost blew up his ChemE roommate in Undergrad, I have to disagree.

One of my Medic certs is as a HAZMAT FRO (First Responder, Operations). In the multi-day training class for that cert, the Fire Captain leading the class showed a video of an underground counterculture "expert" on fabricating explosives at home. Before the video started, he commented, "Be sure to check out his hands...". As the video started the room erupted in laughter -- the "expert" was missing part of 2-3 fingers and one whole finger. Quite the DIY expert...

Also, I'm a pretty good example of a fairly intelligent person being tutored by a much more knowledgeable ChemE on now to make a certain red substance which can be a quite entertaining contact explosive. We had some fun with it around the dorms in Undergrad, but since I didn't really understand the chemistry and limitations behind the synthesis of it, I left a batch I made on my roommate's desk in our dorm room to show him my latest skills. Unfortunately I did not realize how unstable that stuff was under certain conditions, and the batch exploded violently with nobody in the room, ruining the desk and all of the books and schoolwork on it. If my roommate had come home and touched the batch before it went off on its own, he most likely would have been blinded by the explosion and flying glass.

So I vote no on any DIY explosives discussions. I'm glad that @chemisttree explicity listed them as forbidden in his stickie thread...
 
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  • #6
ergospherical
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as ... an EE who almost blew up his ChemE roommate in Undergrad, I have to disagree.
Oooh do tell... what'd he do? Leave the dishes "to soak"? Pinch some of your food from the fridge? :-p
 
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  • #7
berkeman
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Oooh do tell... what'd he do?
He was very upset with me, but I think he realized that he taught me how to make the stuff, and probably omitted parts of the Safety Lecture.

I of course apologize profusely and paid for the repairs and new books that were destroyed. He had to explain to his professors why his homework pages had all of the red streaks and glass cuts through them...
 
  • #8
Vanadium 50
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  • #9
berkeman
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  • #10
Astronuc
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Also, I'm a pretty good example of a fairly intelligent person being tutored by a much more knowledgeable ChemE on now to make a certain red substance which can be a quite entertaining contact explosive. We had some fun with it around the dorms in Undergrad, but since I didn't really understand the chemistry and limitations behind the synthesis of it, I left a batch I made on my roommate's desk in our dorm room to show him my latest skills. Unfortunately I did not realize how unstable that stuff was under certain conditions, and the batch exploded violently with nobody in the room, ruining the desk and all of the books and schoolwork on it. If my roommate had come home and touched the batch before it went off on its own, he most likely would have been blinded by the explosion and flying glass.
The story reminds me of a history teacher from high school who lost a hand and an eye as he retrieved a jar of 'rocket propellant' from the top of a hot car after a student set it on the roof while preparing to enter the school. As soon as he touched it, it exploded, knocked him down, shattered the side of his face, blew off his hand, embedded glass shrapnel in his face and chest, and mangled one of his legs which slipped under the car as it collapsed. It happened years before I had him as a teacher. He was very adamant about student safety and responsibility.
 
  • #11
jack action
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No, as a Medic and an EE who almost blew up his ChemE roommate in Undergrad, I have to disagree.

One of my Medic certs is as a HAZMAT FRO (First Responder, Operations). In the multi-day training class for that cert, the Fire Captain leading the class showed a video of an underground counterculture "expert" on fabricating explosives at home. Before the video started, he commented, "Be sure to check out his hands...". As the video started the room erupted in laughter -- the "expert" was missing part of 2-3 fingers and one whole finger. Quite the DIY expert...

Also, I'm a pretty good example of a fairly intelligent person being tutored by a much more knowledgeable ChemE on now to make a certain red substance which can be a quite entertaining contact explosive. We had some fun with it around the dorms in Undergrad, but since I didn't really understand the chemistry and limitations behind the synthesis of it, I left a batch I made on my roommate's desk in our dorm room to show him my latest skills. Unfortunately I did not realize how unstable that stuff was under certain conditions, and the batch exploded violently with nobody in the room, ruining the desk and all of the books and schoolwork on it. If my roommate had come home and touched the batch before it went off on its own, he most likely would have been blinded by the explosion and flying glass.

So I vote no on any DIY explosives discussions. I'm glad that @chemisttree explicity listed them as forbidden in his stickie thread...
You misread my post. @anorlunda was saying we shouldn't discuss explosives. I agree with that. He was comparing DIY buildings to DIY explosives on the dangerousness level. I disagree with that.
 
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  • #12
berkeman
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Oh, okay. Nevermind...
 
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  • #13
chemisttree
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Or maybe purple.
Yeah, that stuff is purple. It’s so shock sensitive that mud-cracking during drying will set it off. Unsafe at any speed.
 
  • #14
Vanadium 50
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It’s so shock sensitive that mud-cracking during drying will set it off.
It's so shock sensitive that even thinking about touching it will set it off. Best avoided entirely.
 
  • #15
berkeman
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Why weren't you guys in my safety briefing back in Undergrad?
 
  • #16
Vanadium 50
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As an undergrad, I did some pretty dangerous things. Good thing I was luckier then. I also hung with a sketchy crowd who did even more dangerous things (now that they have matured, they do things like nuclear stockpile stewardship). But even then, I avoided the Purple Demon Crystals. The trick to handling it safely? Don't handle it at all.
 
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  • #17
berkeman
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Yeah, good point. In retrospect, that Safety Briefing should have been a short "walk away, son". But I was young and stupid (stupider?), and didn't have my/our future selves to help out.

I guess that's one aspect of Jack's Insights article -- how do you triage forum advice so that it will in fit in as "acceptable" in the Safety Briefing review in the After Action Report? (sorry, too much ICS nomenclature)...
 
  • #18
chemisttree
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Why weren't you guys in my safety briefing back in Undergrad?
I guess I was too busy learning that drying that stuff will paint the walls of your dorm room walls with bits of it.

And when those bits dry....
 
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  • #19
DaveE
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Yeah, good point. In retrospect, that Safety Briefing should have been a short "walk away, son". But I was young and stupid (stupider?), and didn't have my/our future selves to help out.

I guess that's one aspect of Jack's Insights article -- how do you triage forum advice so that it will in fit in as "acceptable" in the Safety Briefing review in the After Action Report? (sorry, too much ICS nomenclature)...
Yes, this the more fundamental problem of risk assessment when you lack data (experience) or have different values. I did lots of stupid s&#@ stuff when I was young and practically none of it would have been prevented by someone saying "I'm older and have more experience than you, I know better, so do what I say."

I agree 100% with @jack action's approach. But, I also wonder if there's a space for saying, slow down, study, think about the possibilities, this is why I wouldn't do that, etc. The question in my mind is are you worried about your role (liability) or do you really want to change someone's mind about doing stupid things.

"We don't talk about that stuff" is easy and probably the correct approach. It's also almost guaranteed to send people some dumb-a&& youtube video that shows exactly how to do what we wouldn't.
 
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