Been lurking for awhile and have a question to bounce off of anybody
who'd like to respond. I built my garage a couple of years ago and
this fall I installed a "Hot Dawg" LP propane heater that hangs from
the ceiling. It has no pilot, being electronically fired, but has
four small burners that send the flame and heat thru some tubing that
the fan then blows down into the garage. I'm starting to work on some
projects that will require some finishing such as sanding sealers,
polyurethane, etc. that list themselves as flammable liquid and vapor.
I called the companies to see what they say about safety given my
situation and they are understandably reluctant to comment on
specifics. My question is: How careful do I need to be around these
products? Obviously, I need high enough temperatures to cure them,
sometimes for 24 hours or so, but if I turn off the heater, and me
being in Maine, it wouldn't take long for the temp in the garage to
get below 55 F. I was thinking that maybe I could crank up the heat
to about 70 F, turn off the heater at the breaker while the fumes were
concentrated and then after I had cracked a window for a bit, I could
turn the heat back on to keep the temps up above 60 F or so until
curing took place. Any thoughts?? Thanks!
As long as you provide a reasonable amount of ventilation and don't spray
flammables directly into the heaters, you should be fine. The fuel to air
ratio has to be in a very well defined range to support combustion, and
you'd have a hard time getting close to that ratio unless you're planning to
aerosol apply quarts of the stuff at a time.
<wp715> wrote in message
About as careful as you'd need to be giving advice on this issue over
I know a guy who knows this stuff. Takes him about two days to write a
safety assessment for a situation like this. Last place he worked had
good safety while he was there, about a year after he left (and they
had had a couple of other people doing the same job) they had a
radioactive fridge fire ! It is _very_ difficult to get to a point
where you can really say "This site and process is safe". No matter
how weird, weird shit can turn up and bite you.
What's easier is to spot an obvious hazard. Mineral spirits is no big
deal, but toluene is nasty. Paint strippers (dichloromethane and
methanol mixtures) can be particularly hazardous as a workshop
flammables hazard. So much is going to depend on just what you're
using, and how much of it. Shellac (in ethanol) is pretty safe around
naked flames, unless you're using large quantities - and then it's a
breathing hazard that needs looking at, as well as a fire risk. Your
biggest "winter risk" is probably the reduced ventilation, as much as
the extra ignition sources. This can raise solvent concentrations to
unusual levels. If you're really worried about flammability, then
consider fitting an LPG alarm - these are sensitive (to varying
extents) to most flammable vapours, not just propane.
Given that this sort of solvent doesn't much like cold weather anyway,
I'd be tempted to look at things like water-based finishes in this
weather, just because they work better. Shellac is unusable here in
the winter (our winters are damp) because the high humidity causes
Without any guarantees, I'd use most workshop solvent-based finishes
from a can and brush, but I wouldn't spray them.
Die Gotterspammerung - Junkmail of the Gods
Interesting. I've only finished three projects with shellac, and I'm still
learning. Are the blooms from the damp mixed with cold, or more a
condition of the damp?
I'm pleased with the results I've gotten so far, down to 40 F and around 60%
relative humidity. Higher relative humidity at higher temps, up to around
100% at maybe 60 F on particularly dank, dreary, but comparatively warm
Are these blooms something that happen immediately, or do I have problems
looming on the horizon?
Michael McIntyre ---- Silvan < email@example.com>
Linux fanatic, and certified Geek; registered Linux user #243621
Combination of both (I think). Don't forget I'm in the UK where
"cold" is between 0 and 5C (just above freezing) but outdoor RH can
be 80%. We don't get those really cold but also very dry winters of
the continental USA. Shellac takes an age to dry at these temperatures
and if it falls in temperature at all (as is likely, if it's in the
workshop overnight) then the RH gets awfully close to condensing.
Die Gotterspammerung - Junkmail of the Gods
Neither does most of the U.S. You really have to get into the northern tier of
states to combine true bitter cold with low humidity. Even much of the east, up
into Maine, doesn't get all that much of the dry winter syndrome...bitter cold,
yes, but not dry. Same with upstate NY for the most part. I spent nearly a
decade in Albany (true upstaters call that mid-state), and though it would bump
25-30 below zip (F.), the humidity was about as high as the air would handle
many days, sometimes whacking 60-80%.
Yeah. It's a great argument for a heated shop, which keeps me away from shellac
here in what the locals like to call MOV--mid-Ohio Valley. Zero F is a big deal
here, but bet on it being wet much of the winter, and we're north of a huge
portion of the U.S.
"In the final choice a soldier's pack is not so heavy as a prisoner's chains."
Dwight D. Eisenhower
I've got a propane Hot Dawg running also and I am not concerning about an
explosive situation. This unit has a very well designed fire chamber.
You need an ungodly amount of flammable vapors present in order to be
concerned like maybe cleaning an engine with gasoline and a brush. By the
time it would be a problem, you would have suffocated before you blew
yourself up. Don't worry about it and if you continue to do so, create some
ventilation to the outside while you are spraying or applying the finishes,
or if you have a dust collector remove the top bag, move it outside and use
it as a fume vacuum by placing the inlet hose close to you work. You will
get a lot of answers from a bunch of anals on this subject, many of which
are overly paranoid.
The Hot Dawg is probably the safest unit on the market.
<wp715> wrote in message
Actually what you have to be concerned about is reaching the lower
inflammable limit (lowest concentration that will ignite) which
will vary considerably with the solvent and the temperature.
It is easy to get to that limit with gasoline and impossible
at ordinary room temperatures with kerosine.
The solvents used in woodworking vary enough that no uniform answer
to your question can be given.
Check to see what the _flash point_ is for the finish or solvent you
will be using. The flash point is the lowest temperature at which
the solvent vapor can be ignited by an open flame, it is essentially
the temperature at which the solvent and the vapor will equilibriate
at the lower inflammable limit.
If the flash point is well above room temperature the concentration
will not rise to the lower inflammible limit even if the room is not
ventilated at all. WHether or not you suffocate or succumb to the
toxic effects fo the solvent vapor is a seperate issue.
Obviously a false statement. It would appear that 'Mike' whomever
he may be, is malicious and wishes to see people harmed.
People who do this sort of thing often explode their vacuum. The
safe way to use forced ventilation to clear inflammible solvents
out of a room is to blow clean air in so that it is clean air passing
through the blower and over the blower motor, or to use an explosion
I dunno if Mike considers me to be anal or overly paranoid but I doubt
that he is as stupid as he sounds. It seems probable that he is actually
Thanks for all the input! Obviously there's a wide variety of opinion
here, but all is appreciated. I guess I'll do some more intensive
research on the particular solvents I'm using and maybe give the State
Fire Marshall a call to boot to see what he thinks. I sure don't want
to blow myself up (just think of all the tools I'd lose!) but don't
want to sit around waiting for warm weather either.
When ever a discussion starts about either finishing vapors or sawdust
particles in the air in the workshop, there is always a chorus of voices
which come in and want you to believe that you will meet your maker if there
is one extra strange molecule floating in the air.
My position is that the concentration of harmful vapors or particles has to
be very very severe, almost to the point of over coming oneself before the
big kaboom. If one uses common sense, and creates a sufficient flow of
fresh air in order to decrease the concentration, there would not be a
problem. Conversely, if the vapors are removed via a vacuum system the same
effect can be achieved.
In fact, to satisfy the most paranoid, one should use water based finishes
I don't consider myself to be malicious like your assumptions state, I
consider myself to be realistic and not wanting to find a problem with every
question or thought. Besides, I've had my share of blowing things up
courtesy of uncle sam for three years.
Your position is factually incorrect and you offer nothing of a
nature to support it.
OTOH, I can tell you about the person I know who was nearly burned to
death, and nearly lost his house to the resultant fire when he
foolishly attempted to dispose of gasoline by pouring it down a florr
drain in his basement. He was no where near suffocating when he
caught on fire.
Perhaps you would like to compare the flashpoint of acetone, commmonly
used in some wood finishes, with that of gasoline.
Or one can substitute knowledge for common sense by reading the label.
Again, check the flash point. The presence of water in the finish
not preclude the presence of inflammable solvents such as petroleum
ethers, which at one time were commonly found in water-based
I am disinclined to attribute to malice that which may be explained by
mere incompetence but there are degrees of incompetence or stupidity
so severe as to be indisitinguishible from malice.
It is one thing to write nonchanalantly that 'I've done that and
don't worry.' It is quite another to write "I've done that and
don't worry, and BTW ignore anyone who actually understands solvent
That last, if not deliberately intended to get people hurt is at best
indistinguuishible from such an effort.
See what I mean about the anal ones coming out to play when ever this
subject comes up.........Fred , you fit the profile.
For you information, flash points are determined by the following procedure.
Flash points are determined experimentally by heating the liquid in a
container and then introducing a small flame just above the liquid surface.
The temperature at which there is a flash/ignition is recognized as the
flash point. Fire point or sustained support of a fire is a more realistic
Further, this is done in a closed vessel with a known volume and the
concentration of vapors is increased with temperature until explosion. In
the case of gasoline it is -40C and Acetone, -17.8C. In fact you can even
get antifreeze to explode if you heat it up enough in a closed vessel.
You really want to imply that a typical woodworker would slosh enough
liquids around to create a concentration equal to that of a small closed
vessel and not be able to physically detect it in the process? Read my posts
Fred, I discuss concentrations as what is critical and surely you can
comprehend that I hope.
As far as the dummy who dumped gas down his drain, all I can say is he
deserved what he got. High concentrations, closed areas, etc, you get it,
Come on Fred, lighten up, open the window and take a deep breath unless you
are in Los Angeles, or maybe you are!!!
Yes, I am familiar with the open cup and closed cup flash point tests.
You make it clear from the rest of your article that you do not know
how to use the information.
Yes indeed, the partial pressure of the vapor over a liquid, commonly
called the vapor pressure, is a function of temperature. Generally,
the flashpoint corresponds to the temperature at which the partial
pressure of the vapor is at the lower inflammible limit.
This means that at a temperature above -40 F you can ignite gasoline
vapors in air. You can do the same for acetone at temperatures
above -17.8 C. That wasn't so hard, was it?
It also means that in a poorly ventilated room if there is a resevoir
of gasoline or acetone available, like an open bucket or a puddle
on the floor the concentration of vapor in the air will equilibrate
at a concentration above the lower inflammible limit for gasoline at
temperatures above -40 F and for acetone at temperatures over -17.8 C.
This equilibrium concentration will only be reached if the rate at
which the vapor diffuses from the room is lower than the rate at which
it evaporates fromt the resevoir. The former rate is determined by
how well the room is vented, the latter by the wet surface area
exposed to the room. This also assumes that the liquid in the resevoir
is not depleted. The time required to reach that equilibrium state
depends on the volume of air in the room, the area of the wet surface
from which evaporation takes place, and how well the air circulates
within the room.
This also assumes that the room is not so tall that stratification
occurs but we are talking about garages, not mine shafts.
Most of those factors are difficult to quantify in the garage workshop.
So? What is the flashpoint of antifreeze? It's above room temperature
isn't it? So it isn't relevent to this discussion eh? Guess what, you
can get water or air to explode if you heat it in a closed vessel.
WTF does that mean?
My comprehension is that you are hoping to get someone hurt. You stated
that the concentration in the room would have to high enough to suffocate
the woodworker before an explosion occurred. That is plainly not true.
Aside from which, if he suffocates he's still dead, isn't he? Did it
occur to you that maybe the woodworker will be wearing a respirator with
activated carbon filters so that he cannot smell the vapor at all?
Or maybe he will leave as soon as he is done applying the finish and
the concentration will rise after he is out of the room? I'm sure
you did, since those are pretty obvious scenarios.
You said he couldn't possibly start a fire at a concentration below that
which would suffocate him. You were wrong but still won't admit it.
You are wasting a lot of bandwidth and time by demonstrating your anal
attitudes for all to see. If it bothers you that much, open the window as I
would if I felt if I were in a dangerous condition like I mentioned in my
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