Hi folks,

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:
http://literature.chart-ind.com/getproductfile.ashx?id=42
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.

Todd Perkins
Safety Director
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.

NOTEs:

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.