Date:

Author: Paul Nord

Subject: Re: flame tube safety question (Exploding can)

Post:

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Dale,

Excellent points about the need for such a demo. I like your
example. Farm kids tend to grow up working around dangerous
equipment. They develop a lot of common sense as a result. But if
we're teaching kids to ignite flammable substances in enclosed
containers... I don't like this so much.

I've got this setup with a cardboard shipping tube. The end of the
tube is plastic. I've rebuilt the hole with a little wood.

I would encourage people not to do this demonstration with metal or
glass containers. Cardboard is plenty strong enough to contain a
small explosion. And if it did detonate, the shrapnel is low-density
and would not have a very long mean-free path through air. Metal or
glass shards will.

Paul


I think that I shall never ski
Again against so stout a tree
A tree whose rugged bark is pressed
in bas-relief upon my chest
a tree that with bacchantic air
wears ski poles in its tangled hair



On Sep 21, 2007, at 12:00 PM, Dale Stille wrote:

>
> Tappers,
>
> OK, I have tried to stay out of the discussion, but now it's friday
> and I need to vent.
> Is this an important demo for physics......probably not unless you
> are doing extensive discussion of gases or fluid mixing.
> ON THE OTHER HAND, most colleges do have some sort of "Physics of
> everyday life, Chemistry and Physics of the Environment, or
> Technology and Society" type course. In this case it is more
> important, because you are teaching about something they are using
> every day. For instance, the fact that the explosion only occurs
> if concentration and enclosure conditions are met can be directly
> applied to the car they drive every day. Those controlled
> explosions in the engine only occur if the gas to air ratio is in
> the range of 3% to 8% with an optimum around 5 to 6%. Anything
> more or less and the car doesn't run.
> Also, we here in the midwest have some regional things that we
> experience maybe more than most that come into play here....mainly
> grain elevator explosions and house explosion from propane leaks
> ( this occurs mostly in the rural areas which is a significant
> portion of our student profile). So, teaching them some safety and
> practical aspects of explosions are worthwhile.
> On a final note, the demo we use is only about 2 liter volume or
> less, and the lid part the comes off is heavier. Makes a small pop
> and the lid goes about 6 ft in the air. Again, a very controlled
> explosion that always works.
>
> Later,
> Dale Stille
> U of Iowa
>
> On Fri, 21 Sep 2007, Richard Berg wrote:
>
>>
>> Doug, et. al.,
>>
>> We do not encourage this type of demo, and do not have this in our
>> list. The uncertainty in exactly how it goes off and inability to
>> avoid the explosion (unlike setting it aside for several hours for
>> the ice bomb) seem to me to be two factors that mitigate against
>> its use.
>>
>> I guess I just want to avoid lawsuits from seriously injured
>> students.
>>
>> Dick
>>
>>
>> *********************************************************************
>> **
>> Dr. Richard E. Berg, Professor of the Practice
>> Director, Physics Lecture-Demonstration Facility
>> U.S. mail address:
>> Department of Physics
>> University of Maryland
>> College Park, MD 20742-4111
>> Phone: (301) 405-5994
>> FAX: (301) 314-9525
>> e-mail reberg@umd.edu
>> www.physics.umd.edu/lecdem
>> *********************************************************************
>> **
>>


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Excellent points about the =
need for such a demo.=A0 I like your example.=A0 Farm kids tend to grow =
up working around dangerous equipment.=A0 They develop a lot of common =
sense as a result.=A0 But if we're teaching kids to ignite=A0flammable =
substances in enclosed containers... I don't like this so =
much.I've =
got this setup with a cardboard shipping tube.=A0 The end of the tube is =
plastic.=A0 I've rebuilt the hole with a little wood.I would encourage people =
not to do this demonstration with metal or glass containers.=A0 =
Cardboard is plenty strong enough to contain a small explosion.=A0 And =
if it did detonate, the shrapnel is low-density and would not have a =
very long mean-free path through air.=A0 Metal or glass shards =
will.PaulI think that I =
shall never skiAgain=A0against so =
stout a treeA tree whose =
rugged bark is pressed=A0in bas-relief upon =
my chesta tree that with =
bacchantic airwears ski poles in =
its tangled hairOn Sep 21, =
2007, at 12:00 PM, Dale Stille wrote:=A0 In this case it is more =
important, because you are teaching about something they are using every =
day.=A0 For instance, the =
fact that the explosion only occurs if concentration and enclosure =
conditions are met can be directly applied to the car they drive every =
day.=A0 Those controlled =
explosions in the engine only occur if the gas to air ratio is in the =
range of 3% to 8% with an optimum around 5 to 6%.=A0 Anything more or less and the =
car doesn't run.=A0 Makes a small =
pop and the lid goes about 6 ft in the air.=A0 Again, a very controlled =
explosion that always works.=A0 (301) 405-5994=A0 =A0 =
(301) 314-9525=A0 reberg@umd.edu

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