• A gas or mixture of gases having, in a container, an absolute pressure exceeding 40 pounds per square inch (psi) at 70° F (21.1° C)
• A gas or mixture of gases having, in a container, an absolute pressure exceeding 104 psi at 130° F (54.4° C) regardless of the pressure at 70° F (21.1° C)
• A liquid having a vapor pressure exceeding 40 psi at 100° F (37.8° C)

Use and storage of compressed gases is strictly regulated according to hazard classification. Select a topic below for more information:

• Hazard classification
• Storage and use
• Additional precautions
• Purchasing

Hazard classification: Compressed gases are classified as class I, II, III, or IV in order of decreasing hazard.* Classes are based on the lethal concentration to 50% of test animals (rats) of each gas (LC50).

* Note: The California Fire Code uses a different classification system. For more information, contact EH&S Fire & Life Safety, (858) 822-5706 or 534-3531.

Storage and use: Storage and use requirements apply to all compressed gases. Read UCSD's Compressed Gas Use and Storage Guidelines for detailed information.

Additional precautions are needed for hazardous gases (classes I, II, and III). Requirements are relaxed for small quantities and short term usage.

• See Safety Requirements for Compressed Gas Use for detailed information on requirements and exemptions.
• See Toxic and Hazardous Gas Classifications to identify the hazardous class of a particular gas.

Purchasing: If you're responsible for ordering compressed gas products, read Marketplace Preview's Compressed Gas Cylinders Overview for details on ordering, services, and rental fees.

• Important: To ensure the safe use and storage of Class I, II, or III gases, contact the Chemical Safety Officer, (858) 822-1579, before ordering material.

Related policies:

UCSD requirements for engineering controls, protective equipment, storage, emergency response, warning systems, and employee training are based on:

• Semiconductor Equipment and Materials International (SEMI) Facility Standards and Safety Guidelines
• Santa Clara County Toxic Gas Ordinance
• Article 80 (Hazardous Materials) of the California Fire Code
• Article 51 (Semiconductor Fabrication Facilities) of the California Fire Code
• National Fire Protection Association (NFPA) Standard 318 (Protection of Cleanrooms)

If you are a UCSD employee with questions, contact an EH&S Research Assistance Program specialist.