On Thu, 30 Oct 2008 17:33:17 -0800, bart wrote:

Hi all,

I hope I'm not too way off base here in asking for advice, but you
guys seem to know everything!! :-)


Boss at work bought a $99.00 environmental chamber and told me to
"make it work".
( this one's sibling:
http://cgi.ebay.com/AES-ENVIRONMENTA...8 6.m20.l1116)

When we recieved it, it didn't "do" anything.
I kept flipping the switch back & forth and eventually some sticky
relays started "working", that is, the heater /fan started working and
the gas solenoid clicked in - depending on the temperature dial.

A label on the back says it is to be cooled with liquid CO2.
Somebody retrofitted it with a 300PSI solenoid - We have since then
gotten a 1000PSI liquid CO2 solenoid.
The wiring in it is OLD and BRITTLE, BTW.

A few hours ago my boss is on my ass to get the cooling working by
next week.
Now I have a basic oxy/acetylene rig at home, but have never played
with liquid CO2.

I'm not exactly sure of what fittings/tubing to use ( copper,
stainless, double flare??).

Also, the boss says that CO2 isn't toxic, so therefore we aren't going
to vent it.
(it's setup in the back of a kitchen, where I work {our "lab"}- with
zero ventilation)

I don't mind doing potentially dangerous stuff in my own garage ( with
the door open), but this is an office full of people.

Am I way off base telling him to hire a professional to do the gas
fitting ( and leave the premises when he runs it without ventilation?)


Just wanted another opinion.

(And yes, I am looking for another job)



Thanks in Advance!

Ordinary copper tubing isn't rated for that kind of pressure. Use
steel or stainless. A visit to a good welding store should get you
some knowledgable advice and the materials you'll need.

All occupied spaces must be ventilated to some extent or the occupants
would eventually suffocate. HVAC systems handle this for normal
occupancy.

Fresh air has a natural CO2 content of about 385 ppm.
Due to the health risks associated with carbon dioxide exposure, the
U.S. Occupational Safety and Health Administration says that average
exposure for healthy adults during an eight-hour work day should not
exceed 5,000 ppm (0.5%).

0.5% - 385ppm = 0.462%. An amount of CO2 necessary to approach this
concentration could be released in a space once per air change. I
think OSHA regs call for a minimum of 4 air changes per hour but there
are various conditions that require more. Ask an HVAC expert about
that or do a bit of web research on the subject.

If you release 125 cubic feet of CO2 in 15 minutes (about one 5' tall
cylinder, 4 air changes per hour), the room/space would need to
contain about 27,000 cu ft of air to achieve the necessary dilution.
With 10 ft ceilings that would be an area of 2700 sq ft.

Scale accordingly for use of less CO2. I strongly doubt that your box
will use CO2 at anywhere near this rate of 500 cu ft/hr. That'd be
about 61 lb of liquid or dry ice.

I recall using boxes like this 40 years ago. Some used liquid CO2,
others dry ice. They weren't very big; a few cubic feet of capacity
inside. They worked surprisingly well, holding set temp to within a
couple of degrees. No special ventilation measures were used. A 10
lb block of dry ice lasted most of an 8 hour shift.