Chapter 13
GASES

Contents

Approved by John Seabury
Revised 2/2002

13.1 Policy
13.2 Scope
13.3 Directory
13.4 General Compressed Gas Systems
13.4.1 Gas Leak Emergencies
13.4.2 Documentation
13.4.3 Training
13.4.4 Gas Cylinder Storage and Use Locations
13.4.5 Gas Cylinders
13.4.6 Gas Flow System
13.4.7 Purge Gas
13.4.8 Vacuum Pumps
13.4.9 Ventilation
13.4.10 Gas Detection
13.4.11 Electrical Systems
13.5 Flammable Gases
13.5.1 General
13.5.2 Scope
13.5.3 Pipes and Components
13.5.4 Gas Cylinder Storage and Use
13.5.5 Ventilation
13.5.6 Gas Detection
13.6 Pyrophoric Gases
13.6.1 General
13.6.2 Scope
13.6.3 Gas Storage and Use
13.7 Health-Hazard Gases
13.7.1 General
13.7.2 Gas Health-Hazard Classification
13.7.3 Small Gas Concentrations and Quantities
13.7.4 Gas Purchase Approval
13.7.5 Gas Delivery and Return
13.7.6 Gas Flow System
13.7.7 Ventilation
13.7.8 Accident Release Evaluation and Control
13.7.9 Gas Detection
13.8 Responsible Parties
13.8.1 Principal Investigator/Supervisor
13.8.2 EH&S – Industrial Hygiene Group
13.8.3 EH&S – Fire Department
13.8.4 Mechanical Engineering
13.8.5 Facilities Department – Maintenance & Operations
13.8.6 Facilities Department – Technical Services
13.9 Glossary
13.10 Standards
13.11 Related PUB-3000 Chapters
13.12 References
13.13 Appendices

Appendix A: Gas Detection System Requirements
Appendix B: Specific Health Hazard Gas Classifications

NOTE:
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13.1 Policy

Berkeley Lab will take precautions to prevent injuries, property damage, and disruption to operations caused by leaks of compressed gas and over-pressurizations. Types of injuries and accidents that will be controlled include:

This policy requires the use of industry-standard gas systems, engineering controls, and administrative controls, as well as training. Higher-hazard gas systems require redundant levels of engineering controls.

13.2 Scope

This policy applies to the storage, use, and handling of gases in pressurized portable containers and gas systems. The primary focus of this chapter is on single-gas uses and systems. Additional requirements apply to:

13.3 Directory

13.4 General Compressed Gas Systems

13.4.1 Gas Leak Emergencies

Hazardous gas leaks that pose a fire, explosion, or health hazard must be reported to the Fire Department (ext. 7911 on site, or ext. 9-911 on Campus) after the area has been evacuated.

Ignition sources in the vicinity of leaking flammable gas should be turned off if an immediate hazard does not exist. A leaking hazardous gas cylinder must not be moved or transported. Room ventilation systems and exhausted enclosures required by this policy should control the hazard until the Fire Department can initiate action. The Fire Department is equipped and trained to contain a leaking gas cylinder in a pressure-rated overpack.

13.4.2 Documentation

Process Safety Documentation

An Activity Hazard Document (AHD) must be developed and approved for all hazardous gas uses that could cause significant injury, property damage, or off-site consequences. (See Chapter 6 for AHD administrative requirements.) Examples of gas uses that typically require AHDs include:

Gas Quantity and Location Control

Total quantities of hazardous gases at specific locations must be controlled. Gas quantity limitations (i.e., exempt amounts) are specified in Tables 3D and 3E of the California Building Code. Gas in quantities up to these exempt amounts may be stored, dispensed, handled, or used within each control area or building (i.e., in the absence of defined control areas). Quantities greater than the exempt amounts require building construction modifications. Contact the Fire Department for specific requirements.

To control quantities of hazardous gases at specific locations, a list of hazardous gases should be maintained at each location. This list will itemize gas quantities and identify storage locations. The Berkeley Lab chemical inventory system can help with this task. The list should be included in the AHD, when appropriate. Typical information on the list includes each gas name and hazard category(ies), number of cylinders, cylinder size(s), total cylinder volume(s) at standard temperature and pressure (STP) in cubic meters (m³) and cubic feet (cf), and maximum allowable quantities by hazard category(ies). When incompatibility separations are required, storage locations for each gas must be noted.

13.4.3 Training

Personnel who operate or work on compressed gas and pressure systems must complete the Berkeley Lab Pressure Safety Orientation (EHS 231). Additional requirements apply to personnel who design or assemble pressure systems. (See Chapter 7, Pressure Safety and Cryogenics.)

Personnel who handle or use hazardous gases must complete the Chemical Hygiene and Safety Course (EHS 348). These personnel must also receive specific training on the hazard and safety procedures for each hazardous gas-use operation, including a review of any AHD. This training is the responsibility of the supervisor.

13.4.4 Gas Cylinder Storage and Use Locations

Exits and Lighting

Storage and use of gas cylinders in exit corridors are prohibited. Hazardous gases must be located away from exit routes and doors, unless located in gas cabinets. Adequate natural or artificial lighting must be provided.

Area Signs

Entrances to all areas where hazardous gases are used or stored must be posted with visible and durable gas hazard identification signs. Hazardous gas exterior storage and use areas must have signs that prohibit smoking within 8 m (25 ft).

Exterior Locations

Exterior storage and use areas must be covered with a noncombustible canopy. These areas must be protected from vehicle damage. Cylinders must not be placed on unpaved ground or on surfaces where water can accumulate.

Combustible Materials Separation

Cylinder storage and use locations must be kept clear of all weeds, grass, brush, and trash, as well as any other combustible materials, for a minimum distance of 5 m (15 ft) from all cylinders. Exception: an approved noncombustible barrier, cabinet, or hood may be used instead (see the Hazardous Materials Separation section, below).

Hazardous Materials Separation

Hazardous gases must be separated from incompatible hazardous materials by distance, barriers, cabinets, or lab hoods, as noted in Table 13.1. See Appendix B for hazard categories of specific health hazard gases. When a gas is classified in more than one category, all compatibilities must be considered and the most stringent separation used. Nonhazardous gases (e.g., inerts) may be stored in any hazard category. When gas cylinders must be separated into hazard categories, each category area will be posted with a hazard category sign.

Safety Shower and Eyewash

An approved safety shower and eyewash will be maintained within 30 m (100 ft) or 10 seconds (whichever is less) of locations where corrosive, eye-irritating, or skin/eye-toxic gases are stored or used.

13.4.5 Gas Cylinders

Cylinder Transportation

Only standard DOT cylinders will be used for transporting compressed gas.

Personnel who are trained to use compressed gases may use standard cylinder carts to transport cylinders within buildings and between adjoining buildings. Carts are preferred, but cylinders weighing 11 kg (25 lb) or less may be hand-carried. Valve-protection caps and plugs must be in place during movement of cylinders. Lecture bottles and other cylinders without protective caps must be transported in standard shipping crates, or an equivalent container.

Gas cylinders must be transported between nonadjoining buildings by a person properly trained, licensed, and equipped to transport gas cylinders. Proper transportation is provided by Berkeley Lab Facilities Transportation or approved Berkeley Lab gas supply subcontractors.

Cylinder Position

Gas cylinders must be stored in a “valve end up” upright position, which includes conditions where the cylinder is inclined as much as 45 degrees from the vertical. Exceptions include cylinders designed for use in a horizontal position, and cylinders with nonliquefied compressed gas that have a water volume less than 5 L (0.18 cf or 1.3 gal).

Cylinder Securing

Gas cylinders must be secured to prevent falling due to accidental contact, vibration, or earthquakes. Cylinders must be secured in one of the following ways:

Cylinder Valves, Caps, and Plugs

Gas cylinders designed to have valve-protection caps and valve-outlet caps and plugs must have these devices in place. Exception: when the cylinder is in use or being serviced.

Gas cylinder valves must have a handwheel, spindle key, or other approved control handle on the valve stem while the cylinder is in use. Cylinder valves should be opened slowly. Cylinder valves seat in both the closed and open position and are likely to leak unless left in the fully open or fully closed position.

Unauthorized Cylinder Modification or Use

All labels, markings, and tags provided on the gas cylinder by the manufacturer must be maintained in good condition. Gas cylinder parts must not be modified, tampered with, obstructed, removed, repaired, or painted by the gas user.

“Empty” Cylinders

Gas cylinders should be left with residual pressure (i.e., typically 200 kPa or 30 psi) to prevent contamination of cylinder contents. Cylinders considered to be empty should be handled with the same precautions as cylinders filled with gas because so-called “empty” cylinders still contain residual gas and pressure. Empty gas cylinders must be labeled “Empty.”

Cylinder Changing

Two people must be present during hazardous gas purge and cylinder change procedures. Reconnected gas fittings must be checked for leaks using a leak-detection fluid or other approved method.

Cylinder Temperature Control

Gas cylinders should be stored in the shade and must not be exposed to temperatures exceeding 50°C (125°F).

13.4.6 Gas Flow System

Pressure Safety

Compressed gas systems must be designed and installed in accordance with the requirements of Chapter 7, Pressure Safety and Cryogenics, except for the following:

Under no circumstances may any gas be used without a standard pressure regulator that is rated for the service.

All pressurized hazardous gas system connections must be leak-checked on new gas systems and after reconnection of any fitting.

Pipes and Components

Gas pipes, valves, fittings, regulators, and related components must be constructed of materials compatible with the gases to be contained and must be rated for the service.

In general, gas systems must be constructed of approved metallic tubing with compression fittings, or better. Where nonmetallic tubing is approved, additional controls may be required. Stainless steel components are preferred. Additional requirements apply to systems covered in Chapter 7.

Pipe Labels

Each gas line outside of the source gas cabinet or lab hood that contains compressed gas must be labeled at least every 6 m (20 ft), at every change in direction, at critical shutoff valves, and as needed to provide clear identification. Labels must be durable and display the gas name and direction of gas flow. Exception: piping that may contain more than one type of gas at various times must have signs or labels posted at the manifold, along the piping, and at points of use, as needed, for clear identification and warning.

Regulators

Gas system pressure must be reduced through a regulator mounted to the cylinder valve outlet or to a manifold installed by the Regulator Shop. Exception: an excess flow valve may be installed between the cylinder valve and regulator. A regulator of the approved type and design for the specific gas and cylinder combination must be used.

Regulators should be inspected by the Berkeley Lab Regulator Shop before installation to ensure that the regulator is the correct one for the particular application and is in safe working condition. Only the Regulator Shop is authorized to alter or repair regulators at Berkeley Lab. Oxygen regulators must be labeled for oxygen service, and used regulators reapplied to oxygen service must be degreased in the Regulator Shop.

Backflow Prevention

Check valves or other backflow prevention devices must be provided when the backflow of materials could create a hazardous condition.

Shutoff Valves

Required emergency shutoff valves must be easily accessible, the valve location identified by means of a sign, and the valve labeled with the gas name or function. Exception: gas cylinder valves do not need to be identified.

An emergency gas shutoff valve must be located at the process equipment utilizing hazardous gas when this equipment is in a different room from the source gas cylinder.

Accidental Flow Control

Excess flow valves (EFVs) or restrictive flow orifices (RFOs) are recommended and may be required by this policy or EH&S to control accidental gas leaks or flows that could cause a fire, explosion, or health risk. Systems with such devices require a Safety Note and must be constructed in accordance with the requirements of Chapter 7, Pressure Safety and Cryogenics.

13.4.7 Purge Gas

When an inert gas source is used to purge hazardous gas from gas lines where different hazard categories of gas are in use at the same time, a separate purge supply must be used for each category of hazardous gas. It is also preferable to have a separate purge cylinder for each hazardous gas cylinder that is in use. Backflow prevention devices must be installed between the purge gas supply and the hazardous gas system.

13.4.8 Vacuum Pumps

The type of vacuum pump oil to be used with gases and chemicals must be analyzed for its compatibility with those gases and chemicals. Hydrocarbon oil should not be used with an oxidizer (i.e., oxygen in concentrations greater than or equal to 25%) or with pyrophoric gases. Inert oils should be used instead. Pumps must have a pressure relief or shutdown device that prevents the pump from bursting if a line becomes plugged. Oil drip pans should be provided under all pump and oil filter assemblies.

13.4.9 Ventilation

General Ventilation Requirements

Exhaust ventilation systems for hazardous gas areas and hazardous gas uses must be installed in accordance with the California Fire and Mechanical Codes and must operate continuously

General area mechanical ventilation for hazardous gas stored and used indoors must be 0.005 m³/s per square meter (one cfm per square foot) of floor area or greater.

Exhausted Enclosures

General Enclosure Requirements

A gas cabinet or lab hood must be used when exhausted enclosures are required for the storage or use of a hazardous gas cylinder. Exception: exhausted process equipment enclosures that meet the same general performance criteria as gas cabinets or lab hoods, as approved by the EH&S Industrial Hygiene Group.

Each lab hood or gas cabinet that contains one or more hazardous gas cylinders must be posted with a sign that identifies the name of the gases and their hazard categories.

Exhausted enclosures for hazardous gases must be constructed of noncombustible materials. Exception: unless approved by the Industrial Hygiene Group based on low gas quantities or concentrations.

Gas Cabinets

Gas cabinets must meet current industry and regulatory specifications, which typically include the following:

Exhaust Duct Systems and Connections

Exhaust systems must be constructed to current building code, fire code, and ACGIH Industrial Ventilation Manual requirements. For example:

The following purge and exhaust systems ancillary to the use of hazardous gas must be connected to the exhaust duct system in an approved manner:

Ventilation Monitoring

All exhausted enclosures must have a ventilation monitor that measures duct or enclosure exhaust performance and displays a quantitative readout easily visible to the gas user (e.g., magnehelic or better).

When ventilation monitoring is required, the monitor must have local audible and visual alarms that activate when the exhaust flow decreases to 70 to 80% of the required air flow.

13.4.10 Gas Detection

General Detection Requirements

Gas-detection controls must be used when significant toxic, flammable, or oxygen-deficiency leak risks cannot be adequately controlled by other means or when required by codes.

Gas-detection controls must not be used in place of proper primary controls (e.g., approved gas lines) and secondary controls (e.g., ventilation and ventilation monitoring). Ventilation monitoring interlocked to automatic gas shutdown at the gas source may also be required.

Requirements for flammable and health-hazard gas-detection procedures are presented in the Flammable Gases and Health Hazard Gases sections of this chapter. Requirements for oxygen-deficiency detection procedures are presented below. When gas detection procedures are required, Appendix A is used to determine gas-detector-system maintenance, audit, responsibility, selection, and installation requirements.

Oxygen-Deficiency Detection

Oxygen-deficiency detection controls may be needed to detect a lack of breatheable air in a space that could be occupied by someone. This situation may be the result of inadequate ventilation or displacement of air by a gas or process byproduct. Guidelines for oxygen-deficiency detection must be developed on a case-specific and hazard basis through Activity Hazard Document and EH&S Integrated Health and Safety Group reviews. Oxygen-deficiency detection controls are generally not recommended when engineering controls (e.g., ventilation) can be used to control the hazard.

Work spaces that may be oxygen deficient and have limited personnel access and egress meet the definition of a “confined space” and must meet all the requirements of the Berkeley Lab Confined Space Program (see Chapter 4, Industrial Hygiene). Portable oxygen detectors, in place of fixed-in-place detectors, are usually sufficient for confined spaces.

13.4.11 Electrical Systems

Electrical equipment and wiring must be installed in accordance with the National Electrical Code. Gas piping and containers must not be designed or placed where they can become part of the electrical circuit or used for grounding.

Required ventilation and control systems must be connected to a standby or emergency source of power to automatically supply electricity in the event of loss of power from the primary source. Exception: when standby power is not available in the building and the gas quantities are below the amounts exempted by the California Fire Code (CFC). Emergency power is required for CFC highly toxic gases in quantities greater than 1 m³ (40°F).

When standby or emergency power is not provided for hazardous gas facilities, controls, or systems that provide primary control against the development of a hazardous condition, loss of system power will activate automatic gas shutoff. Example: an exhaust duct blower that provides exhaust ventilation for flammable or health hazard gas process effluents that continue to be generated after power is lost.

13.5 Flammable Gases

13.5.1 General

See Section 13.4, General Compressed Gas Systems, of this chapter for general requirements for all compressed and hazardous (e.g., flammable) gases.

13.5.2 Scope

The requirements of this section apply to the storage and use of compressed and liquefied flammable gas in quantities less than or equal to 11 m³ or 400 cf (e.g., two size 1A hydrogen cylinders containing about 200 cf each) and greater than 0.6 m³ (20 cf).

The Berkeley Lab EH&S Industrial Hygiene Group , and the Facilities, and Engineering departments can assist in requirements, designs, and construction for the following gas uses, which are not specifically covered in this section:

13.5.3 Pipes and Components

Piping and related gas-flow components must be of approved and noncombustible design and construction. Stainless steel pipe and fittings are recommended. Exception: approved nonmetallic tubing and fittings may be used in lengths up to 1.5 m (5 ft) when flexibility is required, if approved by the EH&S Industrial Hygiene Group.

13.5.4 Gas Cylinder Storage and Use

Interior storage and use rooms must be of noncombustible construction.

Exterior storage and use of cylinders must not be located under a window or within 5 m (20 ft) of smoking, open flames, or other ignition sources. Signs that prohibit smoking within 8 m (25 ft) must be posted. In addition, exterior locations must have a minimum of 25% of the perimeter open to the atmosphere and without walls.

Cylinders of compressed gas in solution and liquefied gas must be stored upright so that the pressure relief valve is in direct contact with the vapor space of the cylinder.

13.5.5 Ventilation

Negative-pressure local exhaust or positive-pressure dilution ventilation is required at all potential leak points in the gas system where the ventilation rate is less than six air changes per hour. Six air changes per hour is approximately 0.005 m³/s per square meter, or one cfm per square foot, of floor area. The EH&S Industrial Hygiene Group will determine when leak-point ventilation is required.

These leak-point ventilation requirements generally do not apply to process equipment that has undergone adequate product safety evaluation and is specifically designed to handle small quantities of flammable gas.

13.5.6 Gas Detection

Flammable gas detection procedures may be required for systems that use heavier-than-air gases, where there is a significant chance that a flammable gas leak could be accidentally ignited in air.

The EH&S Industrial Hygiene Group will determine when this third level of hazard control is warranted. When detection procedures for flammable gas are required, consult Appendix A to determine gas-detector system maintenance, audit, responsibility, selection, and installation requirements.

13.6 Pyrophoric Gases

13.6.1 General

See Section 13.4, General Compressed Gas Systems, of this chapter for general requirements for all compressed and hazardous (e.g., pyrophoric) gases.

See Section 13.7, Health Hazard Gases, of this chapter for information on gas purchase approval, cylinder delivery, cylinder return, and piping and component construction.

Pyrophoric gases include, for example, diborane, phosphine, and silane. Diborane and phosphine are both pyrophoric and CFC Highly Toxic (NFPA Health Hazard Class 4) gases, and therefore require both pyrophoric and toxic (i.e., health hazard) gas safety controls. Silane is a NFPA Health Hazard Class 2 gas, but its primary hazard is its pyrophoricity.

13.6.2 Scope

This section presents general requirements and guidelines for pyrophoric gas use. Additional requirements may apply to the storage and use of pyrophoric gas in quantities greater than 0.3 m³ (10 cf) for gas not in a gas cabinet and 0.6 m³ (20 cf) for gas in a gas cabinet.

13.6.3 Gas Storage and Use

Locations, Barriers, and Cabinets

Whenever possible, silane gas cylinders should be stored and used at exterior locations outside of gas cabinets. Whenever silane is being used outside of a gas cabinet, each silane cylinder should be separated from other hazardous gas cylinders by a 6 mm (0.25 in.) thick steel barrier. Silane cylinders stored or used at exterior locations should be located in shelters or bunkers, or provided with a chain-link fence to restrict entry and reduce the impact of an explosion at the location perimeter. Interior storage and use of silane must be in gas cabinets.

Pyrophoric gas that also has a NFPA health-hazard classification of 3 or 4 must be stored in and used in a gas cabinet. Class 3 or 4 health-hazard gas at Berkeley Lab must be stored and used in an interior area because of code restrictions.

Only single-cylinder gas cabinets must be used for pyrophoric gases.

Pyrophoric gas cylinders located in gas cabinets must have mechanical ventilation at a minimum rate of 1 m/s (200 fpm) air velocity across the cylinder valve and gas fittings with the cabinet access port(s) closed.

Gas Flow Controls

Pyrophoric gas systems at any pressure require a Safety Note.

Remote manual shutdown devices for pyrophoric gas flow must be provided outside each gas cabinet or near each gas panel. Dispensing areas should have an emergency shutdown mechanism for all gases that can be operated at a minimum distance of 5 m (15 ft) from the dispensing area.

Pyrophoric gas flow, purge, and exhaust systems must have redundant controls that prevent pyrophoric gas from igniting or exploding in an unsafe and uncontrolled manner. These controls may include excess flow valves, flow orifices, mass flow controller sizing, process bypass line elimination or control, vacuum-pump inert-gas purging, dilution of process effluent with inert gas and ventilation, controlled combustion of process effluent, ventilation monitoring, and automatic gas shutdown.

13.7 Health-Hazard Gases

13.7.1 General

See Section 13.4, General Compressed Gas Systems, of this chapter for general requirements for all compressed and hazardous (e.g., health-hazard) gases.

13.7.2 Gas Health-Hazard Classification

Health-hazard gases, for the purpose of this chapter, include gases that may cause significant acute or chronic toxic health effects in people at lower concentrations. These gases can, for example, poison someone and/or cause corrosion, irritation, and disease in human tissue.

Acute Health Hazards

Table 13.2 presents standard CFC and NFPA acute-health-hazard gas classifications and shows each category’s relationship to lethal concentration values. These gas classifications must be used to determine which controls in this section are required for each gas use.

Chronic Health Hazards

In contrast to acute-health-hazard gases, chronic-health-hazard gases can be pure or mixed chemicals under pressure in gas cylinders that have significant longer-term health hazards. Examples include OSHA Select Carcinogens (see Chemical Hygiene and Safety Plan). Gases that are only chronic health hazards will be assigned a health-hazard classification and set of engineering controls by the EH&S Industrial Hygiene Group based on the specific gas and use.

Specific Gas Information

See Appendix B for a list of specific health-hazard gases and their corresponding CFC and NFPA classifications. The EH&S Industrial Hygiene Group will assign health-hazard classifications and engineering controls to previously unclassified gases, dilute gases, and gas mixtures.

13.7.3 Small Gas Concentrations and Q uantities

The required controls in this Health-Hazard Gases section only apply to concentrations and quantities of gas that are sufficient to cause a gas-leak health hazard. A hazard exists at all potential leak points where a worst-case gas release will result in a small cloud of gas that is at or above the Ceiling Limit or STEL (or the TWA if no Ceiling Limit or STEL is available).

A leak health hazard exists if the concentration of gas inside the gas source (e.g., cylinder or gas line) is at or above the Ceiling Limit or STEL (or the TWA, if no Ceiling Limit or STEL is available). Exception: when a documented (e.g., in the AHD) gas-release hazard evaluation shows that a leak hazard does not exist. The EH&S Industrial Hygiene Group will approve all leak-hazard evaluations and establish evaluation criteria, as needed.

13.7.4 Gas Purchase Approval

Purchase requisitions for NFPA Health Hazard Classes 3 and 4 gases (and Class 2 gases with poor physiological warning properties), and pyrophoric gases must be approved by the EH&S Industrial Hygiene Group. The gas purchase requisition will be sent to the EH&S Industrial Hygiene Group for approval before purchase. Berkeley Lab Purchasing will not process the requisition until the EH&S Subject Matter Contact approval is obtained.

13.7.5 Gas Delivery and Return

Facilities Transportation must handle all gases that require prepurchase approval, as follows:

13.7.6 Gas Flow System

All gas flow systems at any pressure that handle NFPA Health Classes 2, 3, and 4 gases require a Safety Note and must be designed and constructed in accordance with the requirements of Chapter 7, Pressure Safety and Cryogenics.

13.7.7 Ventilation

Area Ventilation

Area ventilation must be 0.005 m³/s per square meter (one cfm per square foot) of floor area or greater and must be maintained at negative pressure relative to adjacent corridors and nonlaboratory or non-gas-use areas.

General Local Exhaust Requirements

NFPA Classes 3 and 4 gases (and NFPA Class 2 gases with no physiological warning properties): gas cylinders must be kept in laboratory hoods or gas cabinets.

CFC Highly Toxic and Toxic gases (recommended for other NFPA Class 3 gases): all potential gas leak points must be contained within exhausted enclosures.

NFPA Class 3 gases that are not CFC Toxic gases (and NFPA Class 2 gases with no physiological warning properties): all unapproved components in the gas system must be enclosed and exhausted.

Process Equipment Enclosures

When process equipment enclosures are exhausted, ventilation face velocities at all enclosure holes, cracks, and access ports that may need to be opened in a gas emergency must be 0.5 m/s (100 fpm) or greater. Where emergency access is needed, small (not large) access doors must be used to reduce exhaust requirements.

Purge Vents and Exhaust Lines

All lines or ducts carrying purged or exhausted emissions of health hazard gases must be connected to an approved exhaust system.

Corrosive Gas Venting: significant emissions from corrosive gas venting may require the use of an emissions control device (e.g., scrubber) to prevent duct corrosion before the purged gas can be vented into the exhaust duct system.

Ventilation Monitoring and Interlocks

CFC Highly Toxic and Toxic gases: a ventilation monitor with audible and visual alarms is required on the lab hood or gas cabinet where the gas cylinder is kept.

Ventilation monitoring interlocked with automatic gas shutdown may be used in addition to or in place of audible and visual ventilation monitor alarms. In addition, automatic gas shutdown is required based on the gas’s physiological warning properties, as shown in Table 13.3. Ventilation monitoring interlocked with automatic gas shutdown is also recommended for CFC Highly Toxic gases.

13.7.8 Accident Release Evaluation and Control

When required by the EH&S Industrial Hygiene Group, the Activity Hazard Document (AHD) or Safety Note must include an evaluation of the consequences of a worst-case gas release of the largest CFC Highly Toxic or Toxic gas cylinder into the exhaust system. The following release times will be assumed for a worst-case gas release if no flow control devices are provided: 5 minutes for nonliquefied gases and 30 minutes for liquefied gases. If calculations show that IDLH concentrations are exceeded at the exhaust stack discharge, restrictive flow orifices or excess flow valves should be provided in the cylinder valve or as close to the cylinder valve as possible.

When quantities of CFC Highly Toxic gas exceed 1 m³ (40 cf), gas release controls must be implemented to reduce the exhaust stack discharge concentration to one-half of the IDLH at the point of discharge into the atmosphere.

13.7.9 Gas Detection

The following criteria must be used to determine the need for health-hazard gas detection: gas concentration, quantity, and physiological warning properties. Health hazard gas detection is only required when the gas posing a health hazard has poor physiological warning properties. Poor warning conditions exist when the concentration and warning properties of the gas are at or above the Ceiling Limit or STEL (or the TWA if no Ceiling Limit or STEL is available) as determined by Industrial Hygiene. See Table 13.3 for health-hazard gases that require gas detection, ventilation, and gas shutdown controls. Exception: if the aggregate quantity of the health-hazard gas in the control area is less than or equal to 1 m³ (40 cf), ventilation monitoring and gas-source shutdown may be used in place of gas detection.

When gas-detection methods are required, use Appendix A to determine gas-detector system maintenance, audit, responsibility, selection, and installation requirements.

13.8 Responsible Parties

13.8.1 Principal Investigator/Supervisor

The principal investigator or gas-use supervisor has primary responsibility for gas-use safety and implementation of all provisions of this chapter, including:

13.8.2 EH&S — Industrial Hygiene Group

Provides an EH&S hazard evaluation and Code-compliance coordination role related to fire, life-safety, pressure, health, and oxygen-deficiency gas hazards, which includes:

13.8.3 EH&S — Fire Department

13.8.4 Mechanical Engineering

13.8.5 Facilities Department — Maintenance & Operations

13.8.6 Facilities Department — Technical Services

Manages gas supplier subcontracts for all compressed or liquefied gases. The gas subcontractors:

Receive gas orders from Berkeley Lab gas users, provide gases from gas suppliers, deliver gas cylinders to gas requestors, pick up cylinders from gas requestors, and return cylinders to gas suppliers. For return of high-hazard and specialty gases, regardless of vendor, see http://procurement.lbl.gov/lbnl/scottpickup.rtf

Screen gas purchase requests and ensure that requests that require prepurchase approval are not ordered.

Provides the following services related to higher-hazard and speciality gases:

13.9 Glossary

CFC stands for the California Fire Code.

A control area is a space bounded by not less than a one-hour fire-resistive occupancy separation within which exempt amounts of hazardous materials may be stored, dispensed, handled, or used, as defined in the CFC.

A corrosive gas is a gas that can cause visible destruction of, or irreversible alterations in, living tissue (e.g., skin, eyes, or respiratory system) by chemical action.

DOT is the U.S. Department of Transportation.

An exhausted enclosure is a gas cabinet, lab hood, or enclosed compartment that is connected to an approved negative-pressure exhaust duct system.

A flammable gas is a gas that can be ignited in air.

A compressed gas is a material that is shipped in a compressed gas cylinder and acts as a gas upon release at normal temperature and pressure or is used or handled as a gas.

A gas cabinet is an exhausted enclosure used to store or use gas cylinders that meets the requirements specified in this chapter.

A hazardous gas is a gas that is included in one or more of the following hazard categories: corrosive, flammable, health hazard, oxidizer, pyrophoric, reactive, or toxic.

A hazardous-gas detection system is a fixed system used to detect the presence of hazardous gas at potentially unsafe levels.

A health-hazard gas is described in Section 13.7, Health Hazard Gases.

IDLH stands for “immediately dangerous to life and health.” IDLH is a maximum concentration of airborne contaminant to which a person could be exposed for 30 minutes without experiencing escaping-impairing symptoms or irreversible health effects.

A liquefied gas is a liquid contained in a compressed-gas cylinder that has a vapor pressure exceeding 276 kPa at 38°C (40 psi at 100°F).

Lower explosive limit (LEL) is the lowest concentration of a substance in air that will produce a flash of fire when an ignition source is present.

NFPA stands for the National Fire Protection Association.

Oxidizing gas is gas that initiates or promotes combustion in materials, either by catching fire itself or by causing a fire through the release of oxygen or other gases.

Oxygen deficiency is a condition that occurs when a breathable atmosphere contains less than 19.5% oxygen. Note: normal air contains 20.9% oxygen.

Permissible Exposure Limit (PEL) and Threshold Limit Value (TLV) are employee airborne exposure limits established for particular chemicals by the Federal Occupational Safety and Health Administration (Fed/OSHA) and the American Conference of Governmental Industrial Hygienists (ACGIH), respectively. DOE requires that employee exposures must not exceed PELs or TLVs.

Time-Weighted Average (TWA), Short-Term Exposure Limit (STEL), and Ceiling (C) standards are summarized as follows:

Pyrophoric gases are gases that may spontaneously ignite in air at or below 54°C (130°F). Specific gases may not ignite in all circumstances or may explosively decompose.

A Safety Note is a document used to record engineering calculations or tests on specific equipment. A Safety Note may also specify operational requirements addressed in an Activity Hazard Document or in operating instructions. See Chapter 7, Pressure Safety and Cryogenics, for details.

STP stands for standard temperature and pressure.

Threshold Limit Value (TLV) is defined under Permissible Exposure Limit, above.

13.10 Standards

13.11 Related LBNL/PUB-3000 Chapters

13.12 References

13.13 Appendices

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