Lab Safety Guide, Chapter 6 - Compressed Gases
The following gives information on safety, regulations and other topics on the use of compressed gases in the lab. Adapted from the NMSU Lab Safety Guide (modified -dls)
|TABLE OF CONTENTS||
|Chapter 6 Contents: Topics||cont'd|
- 1) Compressed gas cylinders are manufactured and charged under regulations set by the Department of Transportation. These cylinders must not be filled or altered in any way except as specified by the cylinder manufacturer. Cylinders leased under regulations set up by the DOT should never be used to mix gases or be used as a container for anything other than the designated gas.
- 2) A compressed gas is any material or mixture having in the container an absolute pressure exceeding 40 pounds per square inch at 70oF, or regardless of the pressure at 70oF, having an absolute pressure exceeding 104 pounds per square inch at 130oF; or any liquid flammable material having a vapor pressure exceeding 40 pounds per square inch absolute at 100oF.
- 3) Cylinder storage areas must be conspicuously placarded with the names of gases being stored.
- 4) Know the contents of a cylinder and be familiar with the properties of that gas. Never use a cylinder which cannot be positively identified; cylinder color coding varies among gas vendors and is an unreliable identifier of cylinder contents.
- 5) Gas cylinders are equipped with a pressure safety device. There are three types: rupture disks, pop valves and fusible metal plugs. These devices are used separately or in combination on all cylinders. Know the type and location of the relief devices on any cylinder brought into the lab.
6) Fusible metal plugs are designed to melt between 158
and 194oF. Thus, cylinders should not be placed near radiators of heat or in
any location where they may become overheated. Cylinders are designed for safe use up to 122oF.
- 7) Each experimental apparatus employing compressed gas cylinders should be checked for proper pressure relief with the faculty supervisor. The cylinder regulator maximum discharge pressure should not exceed the pressure rating of the downstream apparatus. Be sure all downstream apparatus is at zero gauge pressure before disassembly.
- 8) Federal law requires that cylinders of oxidizing gas have a 20-foot minimum separation from cylinders of flammable gas and that they be securely anchored at all times. Cylinders will not be stored or left unattended in hallways, corridors, stairways, or other areas of access and/or egress. Always store cylinders in a ventilated area away from heat or ignition sources.
- 9) When installing a new cylinder, complete the cylinder information tag, and attach it to the valve stem. Remove the tag and give it to the Departmental Technician when the empty cylinder is returned to the designated storage area, Room 171.
- 10) Use cylinders only with matched connectors and proper Compressed Gas Association (CGA) regulator. Never install cylinder adapters on a regulator. Teflon tape must NEVER be used on any CGA cylinder valve fitting. Section 2 in this chapter describes the regulator inspection program details. Gas cylinder regulators are designed uniquely such that each will only fit a specific cylinder gas type. Left handed threads are found on cylinders containing combustible gases.
- 11) Oxygen regulators should be used only on oxygen tanks. Contamination of oxygen regulators with the oil present in other gases can result in a serious explosion hazard when the regulator is again used for oxygen.
- 12) After regulator is connected to the cylinder, pressure-reducing valve shall be closed before allowing gas to enter the regulator. Gas must not be permitted to enter regulator suddenly.
- 13) Leak-test all connections to a cylinder with a soap solution. CAUTION! Any gas, regardless of its health hazard, may cause asphyxiation by displacing oxygen.
- 14) When removing a regulator from a cylinder, the cylinder valve is closed first, then the pressure is released from the regulator.
- 15) The number of cylinders of flammable gases and oxygen is limited to a maximum of three per laboratory. Connect all cylinders containing flammable gases to an earth ground, and use metallic tubing when connecting these gases to other equipment.
- 16) Cylinders of all gases having a health rating of 3 or 4 and cylinders of gases having a health hazard rating of 2 with no physiological warning properties shall be kept in a continuously mechanically ventilated enclosure. There will be no more than three cylinders of these hazard ratings per hood or other continuously mechanically ventilated enclosure per laboratory.
- 17) Compressed gas cylinders must be firmly secured at all times by a bench or wall mounted cylinder clamp or chain. Pressure-relief devices protecting equipment attached to cylinders of flammable, toxic, or otherwise hazardous gases should be vented to an exhaust duct or fume hood. Regulators with vented bonnets are required when toxic or corrosive gases are used. Securely clamp plastic tubing to the bonnet vent and also at the exhaust duct where the tubing vents, OSHA 29 CFR 1910.101 (2)(b), Compressed Gas Association, Inc. Pamphlet P-1 3.4.4
- 18) When not in use, the regulators on cylinders should be depressurized. If the cylinder is not to be used for a long time, the regulator must be removed and the valve cover screwed into place. Never leave partly assembled apparatus attached to gas cylinders. Never attempt to refill a cylinder.
- 19) When storing or moving a cylinder, always attach the safety cap securely to protect the valve stem, and transport only on a wheeled cart specifically designed for gas cylinders of Size 2 or larger.
20) Any NMSU elevator is a confined space
demanding special precautions when transporting compressed gases. Public
gas cylinders are disallowed on the elevator simultaneously. Sudden release of gas (e.g.,
valve breakage, rupture(d) disk blow-out, etc.) could cause death by asphyxiation.
- 21) Cylinders should be located in the lab so that the cylinder valve is accessible at all times. The main cylinder valve should be closed as soon as it is no longer necessary that it be open (i.e., it should never be left open when the equipment is unattended or not operating). When storing or moving a cylinder, have the cap in place to protect the valve stem and NEVER expose cylinders to temperatures higher than 50 degrees Centigrade (120 degrees Fahrenheit).
- 22) Cylinders of compressed gases must be handled as high energy sources and, therefore, as potential explosives. Cylinder valves should be opened slowly; the valve on an unregulated cylinder should never be "cracked." It is never necessary to open the main cylinder valve all the way; the resulting flow will be much greater than one would ever want. It is safe practice to open the main valve only to the extent necessary. Never tamper with any part of a valve, such as the safety or packing nuts.
- 23) A cylinder should never be emptied to a pressure lower than (20 psig); leave a slight pressure to keep contaminants out, and notify the vendor with a note if draw-down occurs. Empty cylinders should not be refilled by anyone except the gas supplier. Remove the empty cylinder regulator, replace the valve cap, mark the cylinder "MT," and return it to the loading dock storage area for pickup by the gas vendor. Do not store empty and full cylinders together under one chain.
- 24) Cylinder discharge lines should be equipped with approved check valves to prevent inadvertent contamination of cylinders that are connected to a closed system where the possibility of flow reversal exists. Sucking back is particularly troublesome in the case of gases used as reactants in a closed system. If there is a possibility that a cylinder has been contaminated, it should be so labeled and returned to the supplier.
- 25) Departmental Safety Committee approval of high pressure reactor and gas handling system designs are required before apparatus construction begins. Complete a Hazard Review Checksheet or Prior Approval Form for your design and submit it to the Department Safety Committee. Include enough Failure Mode Effect sheets to list all system components.
- 1) The operator of reactors located in barricades or cubicles will enter a
cubicle or open a barricade during a reaction run only on the following conditions:
- A second individual trained in the emergency shut down procedure is actually present in the laboratory as a watchman.
-The operator informs the watchman when he is entering or exiting from the cubicle or opening the barricade.
The watchman may perform other work in the laboratory
BUT MAY NOT LEAVE THE LAB FOR ANY REASON WHILE THE EQUIPMENT OPERATOR IS IN THE BARRICADE OR CUBICLE.
- 2) Users of toxic gases with no physiologic warning (hydrogen sulfide, CO)
will follow the watchman procedure listed above when:
- The cylinder valve is open and the regulator is pressurized and,
- While gas is flowing through a reactor or gas handling system.
- 3) When ordering toxic or flammable gases, request a Flow Restrictor Cylinder Valve (FRV). The FRV orifice considerably reduces the full-open leak rate in event of a major leak (e.g., regulator diaphragm failure).
- 1) All regulators used with toxic or corrosive gas service require a bonnet vent connected to a fume hood or to an operating exhaust duct. Regulators without a bonnet vent must be sent to the vendor for modification.
- 2) A preventative maintenance program is now required for all gas regulators. Corrosive gas service regulators need to be removed from service at semiannual intervals (6 months) for overhaul. Toxic gas regulators are to be sent out for annual overhaul. Anytime a regulator shows gauge pressure discrepancies, bubbles upon leak testing or other abnormal characteristics, it will be removed from service and factory-overhauled.
- 3) The Departmental Technician dates new and rebuilt regulators, records inspection dates and notifies regulator users of inspection-due dates. Inspections are performed annually.
Compressed Gas Association, Inc., Pamphlet P-1994.