Roger,
Propane trailers, as well as anhydrous ammonia trailers have what
is called an "excess flow valve" buried in the tank, unseen to the
naked eye. It works like a one way check valve but allows a
controlled amount of flow before it checks off and stops the flow.
It is there in case an unloading hose ruptures and specifically keeps
the tanks contents from "dumping".
Not to **** you or anyone else off in this group but, I will argue
that there is some irresponsibility involved in talking about of
effective means of terrorism in a public forum. Take the transponder
hijack code discussions after 9/11 that broadcast to the world
something that had been known mainly to pilots and not to the general
public until after that fateful day, for instance. Or the fact that
since the Oklahoma City bombing, the general public now knows how to
build anfo bombs. It is bad enough when law enforcement releases this
kind of information to the public. Please, lets not educate these
radicals ourselves.

Joe Schneider
8437R
Large scale chemical manufacturing industry for over 25 years.
Ammonia, methanol, ammonium nitrate, etc.

"Roger Long" wrote in message
...
snip

The irresponsibility is in the media searching for easy ratings and
the
government for poll bumps by focusing so narrowly on what gets an
easy
response from the public. This deflects attention from the reality
that no
one is paying attention to.

I was driving behind a big propane truck the other day. On the back
is a
three inch pipe with a butterfly valve, the kind that is full open
with a 90
degree turn. The pipe had a cap but it had big grips on it so it
could be
easily removed. I've designed piping systems and had several miles
to study
it so I could see that it would only take about 20 seconds to remove
the
cap, turn the valve, and dump the tank's contents. There was no
locking
device of any kind. A passerby could dump this truck.
snip