Some more holiday curiosity
here in australia many vehicles are powered by LPG which is typically
a propane butane mixture and it is quite cheap at about $0.50 per
litre. On the other hand it costs about $1.50 per litre to fill a bbq
gas cylinder with propane gas. It is in fact illegal to fill a bbq
cylinder with autogas, and people are advised it is quite dangerous to
do so, but there seems to be no consistant reason given for this.
Many believe it results in more CO2 produced during burning. Others
say it will be a hotter flame that the bbq was not designed for. I
have even heard an explanation that the propane and butane liquids
will separate in the cyclinder which of course is rubbish.
One thing that would obviously occur is that taking vapour off the
cylinder of mixed propane and butane must lead to the liquid being
enriched in the higher boiling component ie butane as the cylinder
MTs. but why would that matter? surely either butane or propane will
cook my steak quite adequately? ( I know the vapour pressure curves
for both gases and that pure butane will have no pressure in the
cylinder when the temp gets down to about 0 deg C, but thats pretty
rare in this part of the woods, and if its that cold I aint bbqing no
I am no expert but I assume in vehichle use the car takes the liquid
lpg from the cyclinder so the composition wont be changing with time.
Fuel gases are heavily contaminated and unsuitable for
direct application to food. Here's a collection of
statements about the heavy ends in propane fuels from
Some of these heavy ends (especially if made from
coal) can be aromatics like napthalene, which are
carcinogens and do not burn as readily as short
aliphatics like propane. You'll be painting your
food with carcinogens. Only fools violate the rules.
interesting , I have not yet heard food contact as a reason, and I am
not sure it is valid for the autogas supplied in Australia. I have
forwarded a question to one of our suppliers so it will be interesting
to see if that comes up.
Only fools ( and lazy people) accept rules without questioning
If food contact was such a critical issue I would expect to be able to
find an Australian standard for propane for cooking use. I cannot
( which of course does not mean it does not exist) whereas I have
been able to find a standard for automotive use. On no official site
of gas suppliers in Australia have I seen a reference to not using
autogas for health reasons.
I am not sure what you imply by that remark. I am certainly not
advocating anybody try using autogas in a bbq, I am simply trying to
ascertain for sure why it is illegal ( and I have confirmed that it
is ) Real safety is obtained when you understand the science not the
I imply that others have raised a question about the safety of the gas
source's constituents as being safe for human consumption. Early in
life, we have parents that make rules we have to follow, until they
can convey (if they know) the reasons behind the rules.
You have implied exactly this. You want to know why the cheaper
source cannot be used. If that was not your intent, then you did not
say that in the first place. I understand you are expending
considerable energy distancing yourself from that interpretation /
intent. You don't need to keep doing this, as I'll quit bitching.
Most people are not capable or are not interested in understanding the
"science" behind safety. That is why there *are* laws. In lieu of
having a hungry mind such as yours appears to be, "real safety" comes
from following the laws. You don't need to fabricate homilies to
justify getting your answers.
There is an orifice in gas-fired appliances, that is sized for a
certain heat rate. Its sizing is based on an assumption of the fuel
being evaporated, and the heat rate the appliance can safely produce.
Putting in a different fuel can:
1) clog the works, or damage the seals;
2) produce a very sooty flame, since atmospheric-pressure ignition
temperatures might not be suitable for the mix;
3) produce too much flame, since too much fuel might be allowed to the
4) more (such as contaminants, which I find uncompelling since all
fuel sources are "dirty");
5) not paying the appropriate taxes, allowing people to eat without
Big Brother knowing they are, or more likely using subsidized
transportation fuel for cooking.
I don't find #4 or #5 to be particularly compelling, but I do believe
there to be "mechanical" reasons why it might be a bad idea to cook
with a different blend of (eventually) gaseous fossil fuels.
In general, laws have some justification written into or recorded
"adjacent" for their existence. I'd suggest you go to the text of the
law, to seek out the basis of the law.
David A. Smith
yes and I appreciated that input and said that I would look into it,
in fact I have already sent off an email to a supplier who sells both
propane and autogas . And yes I agree babies and children should
accept what their parents tell them. but I am not a child, I am an
adult and a trained chemist. I ought to be to know why the law is in
place, and frankly I feel a bit embarrassed that I dont, especially
considering I work in the petrochemical industry.
I think you have misunderstood. I am not distancing myself from
anything. Of course I want to know why the cheaper source cannot be
used, its a perfectly logical question to ask, My point was I would
not advocate to anybody else when I do not know myself (yet) whether
there is in fact a danger.
Most people are not qualified chemists and dont read this forum. I am
really lost as to where you are coming from. it seems to me you are
trying to create points of difference that dont exist in order to stir
up an argument. I dont disagree that people should follow the laws,
but law abiding people still get injured in all sorts of accidents
every day. Many of these accidents could have been avoided by having
a better understanding of the science of what they are doing.
Thats all I meant to imply.
And people will always choose to break laws, if they didnt we wouldnt
need police, At least if they understand the reason for the law they
are going to break they are less likely to hurt themselves or others.
For example if we just promulgate the idea that autogas cant be used
for the bbq just because of a food contact reasons, someone might
think it is therefore OK to use it for a gas fired lighting apparatus,
and if in fact if it was the CO problem they are still in danger if
they set the light up in their unventilated garage.
there are certainly heat value differences between butane and propane
but these are small compared to the difference between say methane and
propane , which requires the use of smaller jets in gas burning
appliances. Butane requires 6.5 vs 5.0 parts by volume compared to
propane for complete combustion so it is possible that more CO will be
produced and a sooty flame if enough oxygen is not drawn in by the
burner. but that is something that could be quite easily tested for
( I have access to CO measuring instruments) I have also read many
personal accounts of people already using autogas for cookers etc with
no apparent problems ( which of course doesnt mean there isnt any...
most people would not have access to CO measuring instruments) and it
could well be a significant problem if people were to use it indoors
or without good ventilation.. but again I want to know for sure.
Tax is not an issue here, the high cost of propane vs autogas is
related to the excess of butane available in Australian refineries and
the much larger volumes involved with autogas compared to propane. I
have also since ascertained that the standard for autogas in
Australia dictates a vapour pressure btween 800 and 1530 Kpag at 40
deg C. This would allow anywhere between 0 and about 50 % butane in a
butane / propane mix.
I have, but there is no basis given it is simply stated that it is an
offence to fill a portable cyclinder with autogas.
Thanks for your input.