Compressed Gas: Safety Requirements

Piping, tubes, valves, fittings, and related components must be:

• Designed and fabricated from materials compatible with the material to be contained
• Of adequate strength and durability to withstand the pressure, structural and seismic stress, and exposure to which they are subject
• Identified in accordance with nationally recognized standards to indicate the material conveyed

Examples:

• Hydrogen – Use only stainless steel piping and fittings.
• Oxygen – Use steel, brass, copper or stainless steel (as per National Fire Protection Association regulations).
• Arsine, phosphine, ammonia – Use only stainless steel piping and fittings.

See the section on "Welded, compatible piping" below for additional information.

A continuous gas-detection system is required to detect the presence of gas at or below the permissible exposure limit or ceiling limit.

The detection system must:

• Initiate a local alarm and transmit a signal to a constantly attended control station (exceptions may apply)
• Be capable of monitoring the room or area in which the gas is stored at or below the permissible exposure limit or ceiling limit and the discharge from the treatment system at or below 1/2 IDLH (Immediately Dangerous to Life and Health) limit

The alarm must be both inside and outside the storage area. The audible alarm must be distinct from all other alarms.

An oxygen sensor may be required if it is determined that the location where this compressed gas is being used or stored presents a risk of asphyxiation.

Note: Exceptions to detection systems may exist for class II gases.

Alarm system must be posted with information on:

• What the alarm states mean
• What actions to take
• Who to contact

Emergency power must be provided for these systems:

• Exhaust ventilation (including the power supply for treatment systems)
• Gas cabinet ventilation
• Exhausted enclosure ventilation
• Gas-detection
• Emergency alarm

All laboratories must have an emergency response plan that addresses the use and/or storage of compressed gases.

Review Emergency Preparedness Planning for UCSD to help guide you in this process.

An exhausted enclosure includes gas cabinets and chemical fume hoods.

All Class I and II gases must be kept in an exhausted enclosure at all times.

Class III gases, flammable gases, and oxidizing gases are conditional, depending on the application and the specific gas in question, and will be determined by the EH&S Chemical Hygiene Officer.

Fume hood cylinder storage/use requirements:

• Be certified annually by EH&S for proper airflow.
• Must be approved by the EH&S Chemical Hygiene Officer.Must be properly restrained.

Gas cabinet cylinder storage/use requirements:

• Operate at negative pressure in relation to the surrounding area
• Be provided with self-closing limited access ports or non-combustible windows to give access to equipment controls
  • Average face velocity at the face of the access ports or windows shall not be less than 200 feet per minute (1.01 m/s) with a minimum of 150 feet per minute (0.76 m/s) at any 1 point of the access port or window
• Connected to an approved exhaust system
• Equipped with automatic fire sprinkler system protection, and must be constructed and ventilated according to code requirements.Be provided with self-closing doors
• Be constructed of not less than 0.097 –inch (2.46 mm) (12 gage) steel
• Cabinets containing more than 3 cylinders must be reviewed byEnvironment, Health and Safety to ensure safe storage.
• Be seismically restrained
• Be certified annually by EH&S for proper air flow

Gas cabinet reference guide:

• Thermo Fisher Scientific Inc.

Use a flow-limiting device to restrict hazardous gas flow rates to just over maximum flow required (e.g., flow restricting orifice). These devices must be installed immediately downstream of each gas cylinder.

For small scale experiments, such as fume hood use, a needle valve is sufficient.

For large cylinders, a flow restricting orifice must be installed by the gas supplier in the cylinder valve or installed in the gas purge panel.

An automatic shut down of gas flow must be initiated when any of these conditions occur:

• Hazardous condition is detected
• Seismic disturbance
• Loss of power – see the "Emergency power" section for more information
• Excess-flow-triggered shut-off – Where gases are carried in pressurized piping above 15 psig (103.4 kPa), excess flow control must be provided
• Loss of vacuum
• Loss of cooling
• Loss of ventilation

Gas systems must be leak tested at the following intervals:

• Upon receipt
• At installation
• Periodically during operation
• At disconnect / shipping

It is critical that these gases also be leak tested prior to removal from their exhausted enclosures and subsequent to transport, or if you have reason to believe that the system has been compromised.

The ability to purge the area between the cylinder valve and the regulator with an inert gas prior to maintenance or cylinder change out is required.

Inert gases used for this purpose must be used solely for this purpose and no other operation.

Treatment systems must be designed to reduce the maximum allowable discharge concentration of the gas to 1/2 IDLH (Immediately Dangerous to Life and Health) at the point of discharge to the atmosphere.

When more than 1 gas is emitted to the treatment system, the treatment system must be designed to handle the worst-case release based on the release rate, the quantity, and the IDLH for all the gases stored or used.

Piping and tubing must:

• Have welded or brazed connections throughout unless an exhausted enclosure is provided
• Not be located in any portion of a corridor unless otherwise approved by the UCSD Fire Marshal

See the section on "Compatibile piping" above for addition information.