Model Forum / General / Models / August 2005

I bought some silicone hoses for my car and they were d*mn expensive -
I can see why now...

Samco brand

hi
I think peter may mean an aluminium cleaner, the first aerosol wheel
cleaners had hydraflauric[yes i know i can't spell] acid in them.

The bloke who I saw make hoses worked for silfex or whoever it is that
make samco hoses. He didn't vacum the hose he wrapped it with what
looked like harness wrapping tape[ no adhesive].

richard

Hello Cliff

http://ehs.unc.edu/pdf/HydrofluoricAcid.pdf says:

"Chemical Information Overview
Hydrofluoric acid (HF) differs from other acids because the fluoride
ion readily penetrates the skin,
causing destruction of deep tissue layers, including bone. Pain
associated with exposure to solutions of
HF (1-50%) may be delayed for 1-24 hours. If HF is not rapidly
neutralized and the fluoride ion bound,
tissue destruction may continue for days and result in limb loss or
death. HF is similar to other acids in
that the initial extent of a burn depends on the concentration, the
temperature, and the duration of contact
with the acid."

You can NOT neutralise it once it is in your system. This is what I
meant I say. Make no mistake this is deadly stuff. Further down the
page on the same site it tells this story:

"HYDROFLUORIC ACID FATALITY TO LAB WORKER IN PERTH

Extract from Australian Institute of Occupational Hygienists
Newsletter, December 1994:

An accident in Perth highlighted just how hazardous this acid can be
and it is worth recounting for the
benefit of any lab working or hygienists whose work may involve
advising others who use this substance.
On November 12, a 37 year old man died in the Intensive Care Unit of
Fremantle Hospital after he
accidentally splashed about 100 ml of a 70% solution on his right leg
on October 28. It was estimated that
the extent of the spill covered about 10% of his total body area. The
individual was working as a
technician in a small paleontology laboratory, which was attached to a
private residence. HF is used in
the industry to digest silicates in ore samples. The victim immediately
attempted to remove the spill from
his clothing hosing himself down with a hose attached to a sink in the
laboratory. He then ran from the
laboratory to the swimming pool in the garden, and he remained in the
pool until the ambulance arrived
within the hour. At the time he appeared confused, possibly as a result
of shock.
The following week his right leg was amputated, however despite this,
the individual eventually
succumbed to the toxic effects of the hydrofluoric acid 2 weeks after
the initial spill. There are a number of
points that need to be emphasized as a result of this, which are
relevant to all users of HF:"

Best to avoid the stuff altogether I think.

Peter

No, he is not.

If you replace the word "neutraliser" with "antidote" he is actually correct
(except I haven't come across it in rust removers either - that's usually
orthophosphoric acid).

NaF (sodium fluoride) is okay in tiny doses - but it larger doses it is used
as rat poison.

It is extremely toxic to humans too. The acute oral rat LD-50 is 52 mg/kg,
and the LD-50 acute human ingestion is thought to be similar - the LD-50
acute human inhalation is considerably lower at an estimated 5-10 mg/kg -
inhaling a gram of dust will almost certainly kill you, as will swallowing a
teaspoonful.

Those figures are for sodium fluoride, not for hydrofluoric acid, which is
even more toxic. Hydrofluoric acid also gets into the human system by
absorbtion through the skin.

The real problem with hydrofluoric acid is that it is toxic, not that it is
corrosive. Neutralising it doesn't significantly change the toxicity.

Ionic fluoride is equally as toxic as the acid or as the sodium salt - the
main, small, difference is that the salt is slightly less easily absorbed
through the skin.

The percutaneous (through the skin) action is especially nasty as it numbs
the nerves and there is no pain to tell you that you have been exposed -
this also makes systemic poisoning more likely as well.

There is no antidote for gross systemic fluoride poisoning, whether it is in
the form of hydrofluoric acid or sodium fluoride - both work similarly by
depleting the available calcium in the nerves.

Systemic poisoning takes a while to kill, typically 6 to 24 hours, which
makes NaF a better rat poison - the rats can't easily tell each other what
killed them.

Amputation has occasionally been used in cases where inessential body parts
have been exposed, to prevent death by systemic poisoning. It is the only
known-successful treatment for large-scale acute percutaneous HF insults
(getting too much HF on the skin).

Worse, it only works if you are lucky enough to have only amputatable parts
of the body exposed, a tourniquet is immediately applied after the spillage
and not ever loosened, and you get treatment in a very short time.

Even worse still, there are only a very few doctors in the world expert
enough to be confident and willing to do the amputation - most ordinary
doctors and medics will not even start to consider it before the poisoning
is irreversible.

http://www.uwm.edu/Dept/EHSRM/LAB/hfmedbook.pdf  will tell you about HF
exposure and it's treatment. However the authors, Honeywell, sell more HF
than anyone else, and they kinda gloss over some of the nastier aspects.

For instance: the deaths seem not to have happened; accidental or especially
chronic occupational exposure apparently does not cause skeletal fluorosis
(anything from "scratchy joints" to crippling hunchback arthritis-like
symptoms); and cutting arms and legs off is called "primary excision" and is
only briefly mentioned (on page 11) with only one reference (49).

Rust remover for toilet fixtures sometimes contain dilute hydrofluoric
acid. The concentration is low enough it has the same warnings as any
other product containing a strong acid. I've spilt a drop or two on my
hands in the past with no negative effects.

Whenever hydrofluoric acid is mentioned in a forum like this there is
always someone who has read about its method of interaction with bone
after passing through the skin and they give the same hysterical
warnings. They don't seem to really understand that the interaction is
in the concentration. Seventy percent concentration is very dangerous.
One tenth of one percent is at worst an irritant. But then that goes
for any strong acid. Note the concentration before opening the bottle.
Plan accordingly.

Another example glacial acetic acid can cause severe burns. Dilute
acetic acid is nice in salad dressing.

Cheers,

Kelley

So you roll it like a swiss roll around the former, then treat it (pressure
and/or heat) and it bonds the layers?

Interesting. I'm a bit surprised this works, not because I've particular
knowledge of silicon but just I though silicon tended to be pretty inert.