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Subchapter 1. Unfired Pressure Vessel Safety Orders
Article 1. Scope of These Orders

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§453. Definitions

The following definitions shall apply in the application and interpretation of these Orders.

For definitions directly relevant to LP-Gas, see 1998 Edition of NFPA 58, Section 1-6.

49 CFR: Title 49, Code of Federal Regulations, Parts 100-199.

Acceptable: Capable of performing the particular function specified in the Order with safety.

Air Brake Tank: An air tank 10 inches or less in diameter, having a capacity of 1 1/2 cubic feet or less, and operating at 150 psig or less, and used exclusively to supply air to the braking systems of automotive vehicles and other air-operated auxiliaries used in the operation of such vehicles. The 150 psig limitation need not apply to tanks less than 6 inches in inside diameter.

Air Tank: A pressure vessel used for the storage or accumulation of air under pressure. This definition is not intended to include utilization equipment, including such devices as grease tanks, fire extinguishers, paint sprayers, etc., where the tank is partly filled with a product and the air pressure is used only for a cushion or to eject the product from the tank, or such devices as strainers, scrubbers, separators, etc., that are a part of the piping system.

Alteration: A change in any item described on the original Manufacturer's Data Report which affects the pressure capability of the pressure vessel.

ANSI Standards: Standards approved by the American National Standards Institute, Inc.

(A) Chemical Plant and Petroleum Refinery Piping, ANSI B31.3 (except non-metallic pipe such as plastic is not acceptable unless permitted by specific safety orders).

(B) Refrigeration Piping, ANSI B31.5.

Applicator Tank: A service tank used in agriculture for applying anhydrous ammonia to the soil, or for other agricultural uses.

Approved: See Section 3206, General Industry Safety Order.

Appurtenance: A device installed on and used in the normal operation of the vessel. This includes, but is not limited to, safety relief devices, liquid level gauging devices, valves, and pressure gauges.

Artificial Heat: Any heat other than solar or atmospheric heat.

ASME Code: The American Society of Mechanical Engineers' Boiler and Pressure Vessel Code.

(1) Power Boilers, Section I.

(2) Materials Specifications, Section II.

(3) Nuclear Power Plant Components, Section III, Division 1 and 2.

(4) Heating Boilers, Section IV.

(5) Non-destructive Examination, Section V.

(6) Recommended Rules for Care and Operation of Heating Boilers, Section VI.

(7) Recommended Rules for Care of Power Boilers, Section VII.

(8) Pressure Vessels, Section VIII, Division 1 and 2.

(9) Welding and Brazing Qualifications, Section IX.

(10) Fiberglass-Reinforced Plastic Pressure Vessels, Section X.

(11) Rules for Inservice Inspection of Nuclear Power Plant Components, Section XI.

(12) Power Piping, ASME B31.1 (except non-metallic pipe such as plastic is not acceptable unless permitted by specific safety orders).

(13) Pressure Vessel for Human Occupancy (PVHO), Safety Standard for Pressure Vessels for Human Occupancy.

ASTM: American Society for Testing Materials.

Brittle Failure: A pipe failure mode which exhibits no visible (to the naked eye) material deformation (stretching, elongation, or necking down) in the area of the break.

Bulk Plant:

NH3, CNG, and LNG: An installation other than a dispensing unit, used to store the product for further transfer.

Bulk Storage: Storage in vessels other than DOT cylinders.

California Standard Tank: A tank built in accordance with the requirements for California standard tanks as set forth in the Air Pressure Tank Safety Orders in force at the time the tank was constructed.

Capacity: The gross capacity of a pressure vessel in U.S. Gallons. See “Water Capacity.”

Certificate of Competency: Certification issued by the Division to persons who have satisfactorily passed the written boiler and pressure vessel inspector's examination prescribed by the Division.

Certificate of Resale Inspection: A certificate issued after a resale inspection and designating the maximum allowable working pressure for the tank when it is installed in compliance with these Orders. This certificate is not a permit to operate. This certificate shall expire not more than 5 years from date of inspection or when the tank is returned to service, whichever occurs first.

Certified Inspector: A person holding a valid certificate of competency issued by the Division in accordance with the Boiler and Fired Pressure Vessel Safety Orders.

CNG: Compressed natural gas. Natural gas that has been compressed for storage in containers.

Container Assembly: An assembly consisting essentially of the container and fittings for all container openings, including shutoff valves, excess flow valves, liquid-level gauging devices, safety relief devices, and protective housing.

Container: Any vessel, including tanks, cylinders, tubes, portable tanks and cargo tanks, used for transporting or storing any liquid or gas.

Dike: A concrete, metal, or compacted earth structure used to confine an accidental spill within an impounding area.

Dispensing Unit:

Natural Gas: A stationary natural gas installation other than a bulk plant from which CNG or LNG is dispensed into fuel tanks or portable cylinders from a storage tank, bank of cylinders, compressor, or a distribution gas pipeline.

Division: Division of Occupational Safety and Health.

DOT Service: Service in which a pressure vessel is used, inspected and maintained in accordance with DOT regulations.

DOT Specifications: Regulations of the Federal Department of Transportation published in 49 CFR Parts 100-199.

Ductile Failure: A pipe failure mode which exhibits material deformation (stretching, elongation, or necking down) in the area of the break.

Ductile Plastic Materials: Plastic materials able to withstand external impact from both blunt and sharp objects, while charged with compressed gas under the full rated pressure of the piping system, without brittle failure.

Existing Installations: All pressure vessels installed in California prior to the adoption date of these Orders and in compliance with applicable Safety Orders of the Division in effect at that time and that have not changed ownership and location since the adoption date of these Orders.

External Inspection: An inspection of all visible external surfaces and appurtenances of an installed pressure vessel.

Farm Cart: A vehicle for use on a farm on which is mounted a container of not over 1,200 gallons water capacity.

Field Inspection: An internal and/or external inspection of installed pressure vessels.

Fill, Filling:

(A) Filled by Pressure: A means of filling a pressure vessel whereby the quantity of compressed gas in the vessel at normal temperature is determined by a pressure gauge or gauges.

(B) Filled by Volume: A means of filling a tank or cylinder whereby the volume of liquid in the vessel is determined by measuring the liquid level.

(C) Filled by Weight: A means of filling a tank or cylinder whereby the amount of the product in the vessel is determined by weight.

Flammable Gas: A flammable gas is one with either of the following properties:

(A) At atmospheric pressure and temperature forms a flammable mixture with air when present at a concentration of 13 percent or less (by volume) or which forms a range of flammable mixtures with air wider than 12 percent regardless of the lower limit, or

(B) projects a flame more than 18 inches beyond the ignition source with valve opened fully, or the flame flashes back and burns at the valve with any degree of valve opening, when tested in the Bureau of Explosives' Flame Projection Apparatus.

Flammable Liquid: A flammable liquid is one that has a flash point above 20 degrees Fahrenheit to and including 80 degrees Fahrenheit as determined by Tagliabue's Open-Cup-Method. When the flash point is 20 degrees Fahrenheit or less it is termed an Extremely Flammable Liquid.

Gas: A form of matter having extreme molecular mobility and capable of diffusing and expanding rapidly in all directions.

Gas-Air Mixer: A device, or system of piping and controls, which mixes LNG vapor with air to produce a mixed gas of a lower heating value than the LNG.

GISO: Title 8, California Code of Regulations, Chapter 4, Subchapter 7, The General Industry Safety Orders.

Hazardous: A substance or circumstance which by reason of being explosive, flammable, poisonous, corrosive, oxidizing, or otherwise harmful is likely to cause injury.

Important Building: A building in which there may be a source of ignition under normal operating conditions.

Impounding Area: An area used to contain an accidental liquid spill through the use of dikes and/or topography.


(A) CNG and LNG: Includes natural gas pressure vessels, liquefiers, pumps, compressors and all attached valves, piping and appurtenances affecting the safety of the employment or place of employment. When filling directly from distribution lines by means of a compressor, the installation includes the compressor and all piping and piping components beyond the shutoff valve between the distribution system and the compressor.

(B) NH3: Includes the pressure vessel and all attached valves and other appurtenances affecting the safety of the employment or place of employment.

Labeled: See “Approved.”

Listed: See “Approved.”

LNG: Liquefied Natural Gas. A fluid in the liquid state composed predominantly of methane and which may contain minor quantities of ethane, propane, nitrogen, or other components normally found in natural gas and in a cryogenic state.

Maximum Allowable Working Pressure: The pressure for which a tank was constructed, or if conditions have changed, the maximum pressure permitted at the last inspection by a certified inspector or qualified safety engineer.

Maximum Filling Density: The percent ratio of the weight of gas in the tank to the weight of water that the tank will hold. For determining the water capacity of the tank in pounds, the weight of a gallon (231 cubic inches) of water at 60 degrees Fahrenheit in air shall be 8.32828 pounds.

Metallic Hose: A hose in which the strength of the hose depends primarily upon the strength of metallic parts but it may have non-metallic liners and/or covers.

Mobile Fuel Tank: A vessel mounted on a vehicle or other readily portable device and used only to supply fuel to an internal-combustion engine or other equipment secured to the vehicle or device.

Mobile Storage Module: Assembly of a multiple number of tubes securely fastened within a framework structure and used in DOT service.

Mobile Storage Tank, MST: A tank installed on a trailer or semitrailer, and used temporarily to receive and store anhydrous ammonia. “Temporarily” means not more than 120 days.

Motor Fuel Tank: See Mobile Fuel Tank.

Natural Gas: Naturally occurring mixtures of hydrocarbon gases and vapors consisting principally of methane, either in gaseous or liquid form.

New Installations: All pressure vessels, other than existing installations, installed or reinstalled in a new location after the effective date of these Orders.

NH3: The chemical notation of anhydrous ammonia, a chemical compound composed of nitrogen and hydrogen. It is normally stored and transported as a liquid under pressure. However, in some large storage facilities it is refrigerated and stored at atmospheric pressure.

Nurse Tank: A tank used in agriculture for off-highway service to deliver NH3 from a transportation tank or storage tank to an applicator tank in the field.

Outage: That space required to be left in the vessel to provide for expansion of the liquid by an increase of temperature. For LNG outage is that space required to be left in vessels filled by volume to provide for separation of the vapors resulting from boil-off of the liquid and also to provide for the expansion of the liquid with increase of temperature.

Poison: A substance which when taken in small quantities or low concentrations by mouth, inhaled, or absorbed through the skin rapidly jeopardizes life by other than mechanical or physical action.

Portable Air Tank: An air tank mounted with an air compressor on a towed vehicle.

Portable LNG Tank: A service tank not exceeding 2,000-gallon water capacity used to transport LNG.

Portable NH3 Tank: A service tank not exceeding 1200-gallons capacity used to transport anhydrous ammonia.

Pressure Vessel: An unfired container, including cylinders, used for the storage or accumulation of any gas or liquid under pressure. This definition is not intended to include pressure chambers that are integral parts of such devices as pumps, motors, engines, clothes presses, flatwork ironers, tire molds, etc., where the pressure-containing part is subjected to severe mechanical stresses.

Property Line: A line, imaginary or otherwise, separating a property from adjoining property of public or private ownership.

Pull Away Device: A device installed and anchored so that any tension exceeding the manufacturer's rating on the hose will cause the device to separate and prevent the LP-Gas to escape from both the upstream and downstream lines.

Qualified Person, Attendant, or Operator. A person designated by an employer who by reason of training and experience has demonstrated the ability to safely perform his/her duties and, where required, is properly licensed in accordance with federal, state or local laws and regulations. Reference G.I.S.O. 3207.

Qualified Inspector: Either a certified inspector or a qualified safety engineer.

Qualified Safety Engineer: A person who is qualified to make inspections or examinations of boilers or tanks according to the rules under which the vessel was constructed, and who holds a valid certificate of competency issued by the Division.

Receiving Vessel: A tank or cylinder into which a product is being charged.

Resale Inspection: The inspection of any used vessel to determine its allowable working pressure when reinstalled in accordance with these Orders.

Respiratory Protective Device (RPD): A breathing device designed to protect the wearer from a hazardous atmosphere.

SAE: Society of Automotive Engineers.

Second-hand Pressure Vessel: A used pressure vessel that has changed both ownership and location.

Service Valve: A valve connected directly to a vessel outlet not larger than 3/4-inch pipe size and having an inlet diameter not exceeding the internal diameter of 1/2-inch Schedule 80 pipe for applications other than LP-Gas.

Shop Inspection: Inspection of tanks in a fabricator's shop, or at the job site during erection, as required by the ASME Code.

Standard Dimension Ratios (SDR): A specific ratio of the average specified outside diameter to the minimum specified wall thickness (Do/t) for outside diameter-controlled plastic pipe, the value of which is derived by adding one to the pertinent number selected from the ANSI Preferred Number Series 10 contained in American Society for Testing and Materials (ASTM) Designation No. F412-87a (1987), Standard Definitions of Terms Relating to Plastic Piping Systems which is herein incorporated by reference.

Storage Tank: A tank permanently located and used to store a product or to supply a product to utilization equipment.

Suitable: See “Acceptable.”

Surge Tank: See “Gas-Air Mixer.”

Systems: An assembly of equipment and appurtenances consisting essentially of the container or containers, major devices such as vaporizers, safety relief valves, excess flow valves, regulators, and connecting piping.

Tank: A container, other than a cylinder in DOT service, used for the storage or accumulation of any liquid or gas under pressure. This definition is not intended to include pressure chambers that are integral parts of such devices as pumps, motors, engines, clothes presses, flatwork ironers, tire molds, etc., where the pressure-containing part is subjected to severe mechanical stresses.

Transportation Tank: A tank permanently installed on a truck, trailer, or semi-trailer used to transport a product over the highway.

Trap Tank (Trap Wagon): A tank mounted on wheels for off-highway use and having a capacity of 1200 gallons or less and used to transport LP-Gas from a storage tank to a mobile fuel tank.

Tube: A hollow product of round or any other cross-section having a continuous periphery.

Note: For CNG service, a tube is a seamless, cylindrical-shaped pressure container used in DOT service such as transport trailers.

UM: Unfired Miniature, as Defined in ASME Code Section VIII, Division 1.

Vapor Pressure: The pressure of the vapor (psig) in equilibrium with the liquid at a temperature of 100 degrees Fahrenheit.


LNG Vaporizer: A device used to convert LNG from the liquid to the gaseous state by means of artificial or atmospheric heat.

Ventilation-Adequate: When specified for the prevention of fire during normal operation, ventilation shall be considered adequate when the concentration of the gas in a gas-air mixture does not exceed 25 percent of the lower flammable limit.

Volumetric Filling: The amount of water, in either lb. or gal., at 60oF (15.6oC) required to fill a container full of water.

Weight FIlling: See “Filled by Weight.”

WOG: Water, oil, or gas rating (as applied to valves and fittings).


Authority cited: Section 142.3, Labor Code. Reference: Sections 142.3 and 7622, Labor Code; and Section 13241, Health and Safety Code.


1. Amendment filed 12-8-72 as procedural and organizational; effective upon filing (Register 72, No. 50).

2. Amendment filed 3-28-75; effective thirtieth day thereafter (Register 75, No. 13).

3. Amendment filed 11-7-75; effective thirtieth day thereafter (Register 75, No. 45).

4. Amendment filed 12-14-76; effective thirtieth day thereafter (Register 76, No. 51).

5. Amendment filed 6-15-79; effective thirtieth day thereafter (Register 79, No. 24).

6. Amendment filed 10-18-79; effective thirtieth day thereafter (Register 79, No. 42).

7. Amendment of subsection (a) filed 4-13-82; effective thirtieth day thereafter (Register 82, No. 16).

8. Amendment filed 1-5-88; operative 2-4-88 (Register 88, No. 4).

9. Amendment filed 2-15-90; operative 3-17-90 (Register 90, No. 8).

10. New definitions for “Brittle Failure,” “Ductile Failure,” “Ductile Plastic Materials” and “Standard Dimension Ratios” filed 4-8-92; operative 5-8-92 (Register 92, No. 18).

11. Amendment of section and Note filed 12-4-96; operative 1-3-97 (Register 96, No. 49).

12. Amendment of first two paragraphs filed 1-30-2002; operative 3-1-2002 (Register 2002, No. 5).

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