If you are concerned with the relief valve lifting as a result of over temperature and pressure a solution would be to provide an escape piping arrangement that vents the gas out of the building.
Installation of any escape piping downstream of a safety-relief valve must be designed, fabricated and installed in accordance with applicable codes and standards e.g. ASME, ANSI and Compressed Gas Association etc.
Janet, you make an excellent point. Consider as well that the gas fresh from a liquid cylinder is likely to be colder, therefore more dense than it would be at STP, and sink more readily. A ground level heat source, on the other hand could cause some degree of convection.
Finally, as an asphyxiant gas enters a room it will displace air even more readily if there is someplace for it to go, such as a heat/AC return, crawl space above ceiling tiles, etc.
So your point about having an oxygen monitor - either mounted in the room, externally but sampling the room, or carried by individuals entering the room - is probably the best advice for any indoor storage area, especially if you need to use cryogenic liquids.
Similarly your point about outside storage is also excellent advice. The big gas distributors, such as Airgas, Praxair, and Air Liquide all have access to technicians and engineering teams who can design and install external gas storage and delivery systems. Those are by far the best way to go if your demand for gas justifies it.
Aurgas USA, LLC
Sent from my mobile phone.
Janet Baum <baum.janet**At_Symbol_Here**GMAIL.COM> wrote:
Dear Ralph, Todd Perkins information is very helpful, but there is one other key factor of whether the gas released is heavier than air or not. Using Monona's 1,000 cu. ft. example for a room 10' x 10' x 10' high, if there is a release of liquified gas stored in a small sealed room with minimum ventilation and if there is sufficient volume of gas, a person could suffocate. If the gas is heavier than air and fills the room to say 5'-6' depth, a person in the room could suffocate unless he/she could climb up above the gas fill point. The heavier than air gas displaces room air. Similarly, if the gas is lighter than air, a person would have to drop close to the floor and crawl out to escape suffocation.
This phenomenon is why gas monitors and emergency automatic exhaust ventilation systems are installed in storage rooms with large volumes of cryogenic liquids and why bulk containers are stored outdoors.
Janet Baum, AIA
Washington University in St. Louis
On Fri, Mar 8, 2013 at 5:05 PM, Todd Perkins <p3wt3r**At_Symbol_Here**charter.net> wrote:
One gallon of Cryogenic Liquid Nitrogen expands to 93.11 Cubic feet of gas. Because the only valid way to determine the amount of product in a liquid cylinder is to weigh the cylinder and subtract the cylinder tare weight shown on the DOT Data plate, we use a conversion of one pound liquid to 12.06 Standard Cubic Feet (SCF) of gas per pound at STP.
Cylinder manufacturers use a variety of different names to describe their cylinders, and the names aren't always forthrightly indicitive of the capacity. The best way to determine the product capacity of a liquid cylinder is by the DOT package specification shown on a permanantly affixed data plate AND the rated capacity. Keep in mind that once filled, a liquid cylinder will constantly be loosing product via the pressure relief valve - this is normal and keeps the cylinder from exploding due to pressure buildup. So, a cylinder will not have the exact fill weight except for a very short time.
Below is a "cheat sheet" of the maximum possible gas volumes in Standard Cubic Feet (SCF) for the most common sizes of liquid cylinders. Because there are different fill levels for different cylinders your cylinder may be filled to a different weight.
I got some of this data from Chart, a cylinder manufacturer. They have a resource book that can be downloaded online:
This is an excellent resource.
Another consideration about liquid cylinders - there is no standard rate of off-gassing through the pressure relief valve (PRV); there are far too many variables which affect that rate, so you can't calculate the number of air changes per hour based on a standard rate of gas venting.
NEVER try to prevent the PRV from working - the amount of energy released when the cylinder "FAILS" is terrifying - it will destroy a lab and kill anyone too close. I've seen photos of the aftermath, its not pretty. saving a nickel's worth of gas is not a good reason to endanger the life of everyone around.
Airgas USA, LLC
DOT Max Liquid MAX Max Gas
Package Capacity Product Volume
Spec (L) (Gal) (Lbs.) (cu ft)
4L100 120 31.7 190 2623
4L100 163.6 43.2 259 3575
4L100 186.8 49.4 296 4086
4L100 240 63.4 380 5245
4L200 176 46.5 267 3685
4L200 193 51.0 293 4044
4L200 209 55.2 331 4569
4L200 240 63.4 364 5024
4L200 276 72.9 437 6032
4L292 85 22.5 135 1863
4L292 176 46.5 252 3478
4L292 188 49.7 269 3713
4L292 208 55.0 298 4113
4L292 240 63.4 344 4748
4L292 276 72.9 395 5452
4L292 443 117.0 672 9276
4L412 188 49.7 252 3478
4L412 200 52.8 268 3699
4L412 437 115.5 586 8089
for example a 4L200 with a capacity of 240 Liters (63.4 gallons), will be filled with a MAXIMUM weight of 264 lbs of liquid Nitrogen. That 264 lbs will expand from a liquid into 5024 cu ft of gas - that's a room 20'x25'x 10' tall - completely filled with Nitrogen, no oxygen whatsoever.
1)You might recieve a cylinder that has a product weight less than this MAX amount for many reasons, but you are not likely to receive a cylinder with MORE than this.
2)Weight of product in the cylinder = Total weight (Measured) minus Tare weight (found on cylinder data plate).
Weight of product multiplied by 12.06 = cubic feet of gas.
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