From: "Harry J. Elston"
Date: August 7, 2008 1:23:46 PM EDT (CA) Subject: Re: [DCHAS-L] Cylinder volume units? "SCF" = Standard Cubic Feet It is the volume of the gas when measured at standard temperature/ pressure inside the tank that has been compressed to the maximum operating pressure of the tank. It is NOT THE VOLUME OF THE TANK WITHOUT THE GAS IN IT. For instance, a regular size SCUBA used in diving will hold 80 SCF of dry air when the tank is at 68 F and 3000 psig. I like my fills "Lake Michigan Cold" and in doing so, can usually squeeze a few more pounds of gage pressure out of the cold fill. However, the ideal gas law works both ways and I have found it a costly experiment in physical chemistry to get that "Lake Michigan Cold" fill (from a generous dive shop) then immediately transfer the tank to the bed of a pickup truck on a 100 deg. F summer day. Careful - different people define "standard" differently, especially temperature. Some use 0 C, some use 20 C. Standard pressure is almost always defined as 760 torr, 760 mmHg, 1 atm, 101.325 kPa, or 14.7 psia. However, IUPAC's definition of "standard pressure" changed to 100 kPa because apparently some folks can't handle the thought of a unit with the extra 1.325 units of baggage hanging around. (I will withhold comment regarding certain institutions here. At least NIST still uses 101.325 kPa.) The different definitions of standard temperature is a big "gotcha" on the CIH exam - as they will nearly always put answers for 0 C, 20 C and 22 C as plausible answers. If you want to be utterly analysis-retentive about it, you need to also specify the relative humidity of the gas as well because that will have some affect on the numbers. However, most folks simply use the ideal gas law and be done with it. That's probably more information than you wanted, Margaret. H === From: "paracelcusbombastusvon**At_Symbol_Here**juno.com" Date: August 7, 2008 2:37:58 PM EDT (CA) To: ecgrants**At_Symbol_Here**uvm.edu Subject: Re: [DCHAS-L] Cylinder volume units? SCF as others have stated is standard cubic foot (feet). With regards to compressed gas cylinders this does not refer to the physical internal volume capacity of the cylinder. It refers to the volume of gas at STP the cylinder will contain once the gas has been compressed to the "rated" pressure of the cylinder. Example: the standard approximately 5 foot tall tank contains about 200 cubic feet of gas compressed to about 2250psi. Lynn Knudtson === From: "Russ Phifer" Date: August 7, 2008 1:03:14 PM EDT (CA) Subject: RE: [DCHAS-L] Cylinder volume units? That=92s an easy one=85 standard cubic feet of gas. This is =93quantity=94 , not =93volume=94. The =93standard=94 part there refers to temperature (60=B0F) and (pressure 30 in Hg). Russ Phifer Russ Phifer WC Environmental, LLC PO Box 1718, 1085C Andrew Drive West Chester, PA 19380 610-696-9220x12/ fax 610-344-7519 rphifer**At_Symbol_Here**wcenvironmental.com === From: Laurence Stock Date: August 7, 2008 1:09:25 PM EDT (CA) Subject: Re: [DCHAS-L] Cylinder volume units? Standard Cubic Foot === From: Jane McNeil Date: August 7, 2008 1:09:58 PM EDT (CA) Subject: Re: [DCHAS-L] Cylinder volume units? standard cubic feet, perhaps? Jane === From: Kent Candee Date: August 7, 2008 1:20:16 PM EDT (CA) Subject: Re: [DCHAS-L] Cylinder volume units? standard cubic feet Kent A. Candee, CIH Assistant Secretary Environmental Health Services Manager Home Office Risk Improvement EMC Insurance Companies Ph: 515-345-2728 Cell: 515-321-5874 Fax: 515-345-2220 www.emcinsurance.com Count on EMC for Loss Control Services
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