PSFC Compressed Gas


Plasma Science and Fusion Center

Office of Environment, Safety, and Health


190 Albany Street, NW21 2nd floor
617-253-8440 (Catherine Fiore)
617-253-8917 (Matt Fulton)
617-253-5982 (Bill Byford)
617-258-5473 (Nancy Masley)
Fax 617-252-1808

Be Safe or Die


Standard Operating Procedures for the Handling and Use of Compressed Gases.

Reviewed and Approved By:

Jim Irby PSFC Supervisor

Andrew Kalil MIT EHS, PSFC Team member

Catherine L. Fiore, PSFC Safety Officer

Author: A. Eckmann/C. Greenspan

Version: 1.5

Date: March 20, 1992. Modified by C. L. Fiore 12/15/1998 and 5/24/2007

Persons Responsible: All Supervisors Using Compressed Gases

Introduction:

This document outlines the hazards involved with the handling and use of compressed gases. It details the procedures to be followed to minimize the risk of exposure of Plasma Science and Fusion Center employees to toxic gases and the potential explosions or fires associated with their misuse. The compressed gases most commonly used at the Plasma Science and Fusion Center are:

• Argon

• Carbon Dioxide

• Acetylene

• Helium

• Hydrogen Chloride

• Oxygen

• Methane

• Diborane

• Nitrogen

• Hydrogen

• Sulfur Hexafluoride

Compressed gases are definedby the U.S. Department of Transportation (DOT) as any materials or mixtures in containers having an absolute pressure in excess of 40 psi at 20 C (70 F) or in excess of 104 psi at 54.5 C (130 F).

Scope:

This procedure covers employee safety during the handling and use of compressed gas cylinders at the PSFC. This document incorporates the MIT policy on compressed gases as it relates to the PSFC. More general policy information on compressed gas usage at the Institute can be obtained through the Safety Office.

 

Safety Analysis:

Handling of compressed gases may be considered more hazardous than the handling of liquid and solid materials because of the following properties: high pressure, ease of diffusion, low ignition points for flammable gases, low boiling points, and in some cases lack of visual and/or odor detection of hazardous gases. Because of these properties, failure to follow proper procedures can result in both personal and property damage.

Following are some of the hazards associated with the improper handling and use of compressed gases:

General Hazards

  1. Explosion hazards may arise as a result of equipment failure or leakage from systems that are not pressure tight. Explosion can also occur if the compressed gas is used to pressurize system elements such as tubing, vacuum vessels, or any other type of containment beyond their design ratings.
  2. Diffusion of leaking gases may cause rapid contamination of the atmosphere, giving rise to toxicity, anaesthetic effects, asphyxiation, and rapid formation of explosive concentrations of flammable gases.
  3. The ignition point of a flammable gas under pressure is always lower than the ambient or room temperature. Leaking gas can, therefore, rapidly form an explosive mixture with air.
  4. Low-boilingpoint materials can cause frostbite on contact with living tissue. This is common among the cryogenic liquids, such as nitrogen and oxygen, but it also can result from contact of the liquid phase of liquified gases, such as carbon dioxide, fluorocarbons and propylene.

The procedures adopted for the safe handling of compressed gases are based on containment of the material so as to prevent its escape into the atmosphere and to maintain proper flow and pressure. The specific hazards of compressed gases used at the PSFC are as follows:

GAS

THRESHOLD LIMIT VALUE (TLV) PPM

FLAMMABILITY

LIMITS IN AIR

(% BY VOLUME)

MAJOR HAZARDS

ACETYLENE

not established.

2. 5-81.0

flammable,as-
phyxiant, prod. anesthetic effects *

ARGON

not established.

none

asphyxiant

CARBON DIOXIDE

5000

none

asphyxiant

DIBORANE

0.1

0.8-98.0

toxic, flammable, pyrophoric

ETHANE

not established.

3.0 - 12.5

flammable, as phyxiant, prod. anesthetic effect

HELIUM

not established.

none

asphyxiant

HYDROGEN

not established.

4.0-75.0

flammable, asphyxiant **

HYDROGEN
CHLORIDE

5

none

toxic, burns, corrosive

METHANE

not established.

5.3-14.0

flamm., asphyx.

METHYL MERCAPATAN

0.5

unknown

toxic, flammable

NITROGEN

not established.

none

asphyxiant

OXYGEN

non toxic

none

highly reactive ***


SULFUR HEXAFLUORIDE

5000

none

asphyxiant, very dense

*ACETYLENE CAN EXPLODE WITH EXTREME VIOLENCE IF IGNITED. Gaseous acetylene may also decompose with explosive force and should not be used at pressures in excess of 15 psig (30 psi absolute pressure). Special cylinders have been engineered to contain acetylene under moderate pressure (250 psi at 70 F). This is done by dissolving the acetylene in acetone. All acetylene cylinders should be stored and used upright to prevent the escape of acetone.

**When over 400 cubic feet (two standard 1A cylinders manifolded) of Hydrogen are used it becomes a system that is tightly regulated by the Federal government. The MIT EHS Office is prepared to assist in planning hydrogen systems and installations.

***OXYGEN UNDER PRESSURE WILL RAPIDLY OXIDIZE OIL OR GREASE, RESULTING IN AN EXPLOSION. NEVER use oil or grease on valves or gages intended for oxygen cylinders. Use only oxygen service regulators and components.

Definitions:

Asphyxiant gas - A gas which has little or no positive toxic effect but which can bring about unconsciousness and death by replacing air and thus depriving an organism of oxygen.

Flammable gas - A gas mixture of 13% or less by volume with air that is ignitable at 14.7 psia or has a flammable range with air of at least 12% regardless of the lower limit.

Pyrophoric gas - A highly flammable and reactive gas that may spontaneously burn or explode when released into the air.

Oxidizing gas - A gas that, in the presence of an ignition source and a fuel, supports and may vigorously accelerate combustion.


Threshold Limit Value (TLV) -
The time-weighted average concentration for a normal 8-hour workday and a 40 hour work week, to which nearly all workers may be repeatedly exposed without adverse effects.


Explosive or Flammable Limits or Range (Lower & Upper - LEL & UEL) -
The minimum and maximum concentration of a gas or vapor in air within which a substance will burn or explode when exposed to an ignition source.


Responsibilities:

The supervisor or responsible person shall designate and train employees who are required to handle and use compressed gases. The supervisor or responsible person shall ensure that necessary safety equipment is available. The supervisor or responsible person shall ensure that compressed gases are handled in accordance with good work practices. It is the supervisor's responsibility to verify that employees using compressed gases understand the proper procedures.

Assumptions:

The supervisor or responsible person shall be familiar with the hazards associated with compressed gases and the appropriate procedures and equipment necessary for proper handling as outlined in this document.

Procedures:

The following procedures define the proper receiving, transporting, handling and use and disposal of compressed gases at the PSFC.  (Note: the use of diborane gas in the Alcator C-Mod experiment is covered by a separate set of procedures.  See Diborane gas installation/deinstallation procedure and Emergeny procedures for diborane gas system.)

RECEIVING

  1. When a cylinder is received from a supplier it should have a valve protection cap, a DOT label, the date of the last hydrostatic test and labels identifying the contents.
  2. Cylinders received with only color coding should NOT be accepted, as there is no universal color code for identifying gas cylinders.
  3. Cylinders must be secured against falling upon receipt, or transferred to the point of use and secured there.

STORAGE

  1. Compressed gas cylinders should be stored in a level, dry fire resistant area that is well ventilated. The storage area should be separated from the area where the gas cylinders are used by distance or by physical barriers.
  2. Store cylinders away from sources of ignition or excessive heat. Pressure-relief devices are installed on flammable gas cylinders and most other cylinders to prevent cylinder rupture in the event of fire or high temperatures.
  3. Store oxygen away from flammable gases. Oxygen should be stored at least 25 feet away from flammable gases or separated by a five ft. high non-combustible wall.
  4. Do not store cylinders near elevators, gangways or in locations where moving objects may strike or fall on them.
  5. Cylinders must be chained or strapped in place to prevent then from falling over. A falling cylinder may shear off its valve causing the escape of high pressure gas resulting in an explosion or the rapid projection of the bottle and/or valve. A 250 cu . ft. cylinder pressurized at 2500 psi, with the valve broken off, becomes a rocket and attains a speed of 35 MPH in 0.1 second. Store cylinders with valve caps securely attached whenever cylinders are not in use.
  6. Corrosive gases should be stored for the shortest possible time period to prevent corrosion of valves, labels and regulators, and to avoid potential leakage.

TRANSPORTING

  1. Always use a hand truck to transport cylinders. Do not drag, roll or slide cylinders. Leave the valve protection cover ON until cylinders are secured and ready to use. Do not transport a cylinder with the regulator installed.  Do not use a transport device to hold a cylinder in use unless it is adequately secured from falling.
  2. Do not transport compressed gases in closed vehicles. Cylinders must be chained or otherwise secured during transporting in a open or well ventilated vehicle.
  3. Flammable gases and oxygen should not be transported in the same vehicle.
  4. Always handle cylinders as if they were full. Accidents have occurred when containers were under partial pressure and were thought to be empty.
  5. If it is necessary to transport gas bottles with a crane, forklift, or other lifting fixture, an approved carrier designed for that purpose must be used.

HANDLING AND USE

  1. Before use, an evaluation of the operation should be made and appropriate safeguards instituted. The major hazard of a compressed gas is often a function of how and where it is used.
  2. The cylinder valve should be positioned sothat it is accessible at all times. The main valve MUST be closed when the cylinder is not in active use. NEVER use wrenches or pliers to open the main valve unless it is a specially designed key provided by the supplier. Most cylinders are equipped with a hand wheel valve. If the valve is not operational, return to supplier labeled "inoperable".
  3. NEVER crack open valves on unregulated cylinders. The main valve on a regulated cylinder should be opened slowly. The main valve should NOT be opened all the way. Never face a gage while opening a cylinder. Stand to the side in case of a malfunctioning valve.
  4. With the cylinder valve open and the flow control valve in the closed position, set the desired delivery pressure by turning the delivery pressure adjusting screw clockwise until the desired pressure is reached. While the function of the regulator is to set and maintain a given gas delivery pressure, flow control is achieved by the use of the flow control valve located at the regulator outlet or by a supplementary needle valve.
  5. Always turn off the cylinder by first closing the main cylinder valve and then the regulator. The pressure gages should be brought back to zero.
  6. When cylinders containing different gases are manifolded, one way or check valves should be placed on line to prevent accidental gas mixtures due to pressure differences.
  7. NEVER strike an electric arc on or direct a flame at a cylinder.
  8. Appropriate personal protective equipment (goggles, face shields, glo ves) should be worn with compressed gases.
  9. Never pressurize a sealed system unless a pressure relief valve is installed on the system or it is rated to take the full bottle pressure without explosion.
  10. Process piping must be provided in accordance with NFPA 55 and ANSI B-31.1. CGA fittings should be used. Manifolding should be constructed by a certified pipe fitter qualified to work with high pressure systems.
  11. Do not use a transport device to hold a cylinder in use unless it is adequately secured from falling.

ADDITIONAL CONSIDERATIONS FOR TOXIC AND FLAMMABLE GASES

  1. Toxic, flammable and corrosive gases should be used in a well ventilated area or fume hood. Gases with a health hazard label of 3 or 4 must be used in an approved gas cylinder cabinet.  Pyrophoric gases must be used in an approved gas cylinder cabinet equipped with a sprinkler system.
  2. Users of flammable gas cylinder sizes in laboratories must consider fuel loading when choosing the size and number of cylinders. The amount of cylinder gas necessary to stay below the lower explosive limit should be evaluated.
  3. Ground all cylinders and piping containing flammable gases to prevent the hazards caused by the buildup of static electricity.
  4. NEVER use oil or grease on valves or gages intended for oxygen cylinders. Use only oxygen service regulators and components.

LEAK DETECTION

  1. Suspected cylinder leakage should be tested by covering the cylinder with soapy water. A leak will be indicated when bubbles of escaping gas pass through the soap film.
  2. Keep connections to piping, regulators and other appliances tight.
  3. Check that hoses are in good condition.
  4. If a gas cylinder is leaking, the supplier should be notified for advise on how to handle the leak until the supplier can remove it from the laboratory.
  5. If a leaking cylinder is judged safe to handle, it may be placed in a hood or moved to an outside location.

DISPOSAL

  1. Mark empty cylinders "empty" and store separately from full ones. NEVER refill a cylinder. A cylinder is empty at 25 psi. DO NOT EMPTY COMPLETELY as suction and backflow can occur contaminating the cylinder.
  2. Most compressed gases are now available from suppliers in returnable cylinders. Detailed procedures concerning returnable cylinders are outlined in the PSFC Chemical Hygiene Plan. It is very important that returnable cylinders be used when possible as the cost of disposing of non-returnable cylinders is prohibitive.

References:

MIT Accident Prevention Guide, 6-1Compressed Gases.

MIT EHS: SOP#EHS-001 Compressed Gases

Prudent Practices in the Laboratory, Chapter 6.D Working with Compressed Gases. National Academy Press, Washington, D. C., 1995.

This page maintained by Catherine L. Fiore FIORE@PSFC.MIT.EDU