Section 6004 Highly Toxic and Toxic Compressed Gases
Toxic and highly toxic compressed gases shall not be stored or used within Group A, E, I or U occupancies.
Exception: Cylinders not exceeding 20 cubic feet (0.566 m3) at normal temperature and pressure (NTP) are allowed within gas cabinets or fume hoods.
Toxic and highly toxic compressed gases shall not be stored or used in offices, retail sales or classroom portions of Group B, F, M or S occupancies.
Exception: In classrooms of Group B occupancies, cylinders with a capacity not exceeding 20 cubic feet (0.566 m3) at NTP are allowed in gas cabinets or fume hoods.
Gas cabinets containing highly toxic or toxic compressed gases shall comply with Section 5003.8.6 and the following requirements:
- The average ventilation velocity at the face of gas cabinet access ports or windows shall be not less than 200 feet per minute (1.02 m/s) with not less than 150 feet per minute (0.76 m/s) at any point of the access port or window.
- Gas cabinets shall be connected to an exhaust system.
- Gas cabinets shall not be used as the sole means of exhaust for any room or area.
- The maximum number of cylinders located in a single gas cabinet shall not exceed three, except that cabinets containing cylinders not exceeding 1 pound (0.454 kg) net contents are allowed to contain up to 100 cylinders.
- Gas cabinets required by Section 6004.2 or 6004.3 shall be equipped with an approved automatic sprinkler system in accordance with Section 903.3.1.1. Alternative fire-extinguishing systems shall not be used.
Exhausted enclosures containing highly toxic or toxic compressed gases shall comply with Section 5003.8.5 and the following requirements:
- The average ventilation velocity at the face of the enclosure shall be not less than 200 feet per minute (1.02 m/s) with not less than 150 feet per minute (0.76 m/s).
- Exhausted enclosures shall be connected to an exhaust system.
- Exhausted enclosures shall not be used as the sole means of exhaust for any room or area.
- Exhausted enclosures required by Section 6004.2 or 6004.3 shall be equipped with an approved automatic sprinkler system in accordance with Section 903.3.1.1. Alternative fire-extinguishing systems shall not be used.
One or more gas cabinets or exhausted enclosures shall be provided to handle leaking cylinders, containers or tanks.
Exceptions:
- Where cylinders, containers or tanks are located within gas cabinets or exhausted enclosures.
Where approved containment vessels or containment systems are provided in accordance with all of the following:
- 2.1. Containment vessels or containment systems shall be capable of fully containing or terminating a release.
- 2.2. Trained personnel shall be available at an approved location.
- 2.3. Containment vessels or containment systems shall be capable of being transported to the leaking cylinder, container or tank.
In addition to the requirements of Section 5003.2.2, piping and controls on stationary tanks shall comply with the following requirements:
Pressure relief devices shall be vented to a treatment system designed in accordance with Section 6004.2.2.7.
Exception: Pressure relief devices on outdoor tanks provided exclusively for relieving pressure due to fire exposure are not required to be vented to a treatment system provided that:
- The material in the tank is not flammable.
- The tank is not located in a diked area with other tanks containing combustible materials.
- The tank is located not less than 30 feet (9144 mm) from combustible materials or structures or is shielded by a fire barrier complying with Section 6004.3.2.1.1.
- Filling or dispensing connections shall be provided with a means of local exhaust. Such exhaust shall be designed to capture fumes and vapors. The exhaust shall be directed to a treatment system in accordance with Section 6004.2.2.7.
Stationary tanks shall be provided with a means of excess flow control on all tank inlet or outlet connections.
Exceptions:
- Inlet connections designed to prevent backflow.
- Pressure relief devices.
Gas rooms shall comply with Section 5003.8.4 and both of the following requirements:
- The exhaust ventilation from gas rooms shall be directed to an exhaust system.
- Gas rooms shall be equipped with an approved automatic sprinkler system. Alternative fire-extinguishing systems shall not be used.
The exhaust ventilation from gas cabinets, exhausted enclosures and gas rooms, and local exhaust systems required in Sections 6004.2.2.4 and 6004.2.2.5 shall be directed to a treatment system. The treatment system shall be utilized to handle the accidental release of gas and to process exhaust ventilation. The treatment system shall be designed in accordance with Sections 6004.2.2.7.1 through 6004.2.2.7.5 and Section 510 of the International Mechanical Code.
Exceptions:
Highly toxic and toxic gases—storage. A treatment system is not required for cylinders, containers and tanks in storage where all of the following controls are provided:
- 1.1. Valve outlets are equipped with gas-tight outlet plugs or caps.
- 1.2. Handwheel-operated valves have handles secured to prevent movement.
- 1.3. Approved containment vessels or containment systems are provided in accordance with Section 6004.2.2.3.
- Toxic gases—use. Treatment systems are not required for toxic gases supplied by cylinders or portable tanks not exceeding 1,700 pounds (772 kg) water capacity where a gas detection system complying with Section 6004.2.2.10 and listed or approved automatic-closing fail-safe valves are provided. The gas detection system shall have a sensing interval not exceeding 5 minutes. Automatic-closing fail-safe valves shall be located immediately adjacent to cylinder valves and shall close when gas is detected at the permissible exposure limit (PEL) by a gas sensor monitoring the exhaust system at the point of discharge from the gas cabinet, exhausted enclosure, ventilated enclosure or gas room.
The maximum flow rate of release for portable tanks and cylinders shall be calculated based on the total release from the cylinder or tank within the time specified in Table 6004.2.2.7.5. Where portable tanks or cylinders are equipped with approved excess flow or reduced flow valves, the worst-case release shall be determined by the maximum achievable flow from the valve as determined by the valve manufacturer or compressed gas supplier. Reduced flow and excess flow valves shall be permanently marked by the valve manufacturer to indicate the maximum design flow rate. Such markings shall indicate the flow rate for air under normal temperature and pressure.
| VESSEL TYPE | NONLIQUEFIED (minutes) | LIQUEFIED (minutes) |
| Containers | 5 | 30 |
| Portable tanks | 40 | 240 |
Emergency power shall be provided for the following systems in accordance with Section 604:
- Exhaust ventilation system.
- Treatment system.
- Gas detection system.
- Smoke detection system.
- Temperature control system.
- Fire alarm system.
- Emergency alarm system.
A gas detection system complying with Section 916 shall be provided to detect the presence of gas at or below the PEL or ceiling limit of the gas for which detection is provided. The system shall be capable of monitoring the discharge from the treatment system at or below one-half the IDLH limit and shall initiate a response in accordance with Sections 6004.2.2.10.1 through 6004.2.2.10.3 if the gas detection alarm is activated.
Exception: A gas detection system is not required for toxic gases when the physiological warning threshold level for the gas is at a level below the accepted PEL for the gas.
The gas detection system shall initiate a local alarm and transmit a signal to a constantly attended control station when a short-term hazard condition is detected. The alarm shall be both audible and visible and shall provide warning both inside and outside the area where gas is detected. The audible alarm shall be distinct from all other alarms.
Exception: Signal transmission to a constantly attended control station is not required where not more than one cylinder of highly toxic or toxic gas is stored.
The gas-detection system shall automatically close the shutoff valve at the source on gas supply piping and tubing related to the system being monitored for whichever gas is detected.
Exception: Automatic shutdown is not required for reactors utilized for the production of highly toxic or toxic compressed gases where such reactors are:
- Operated at pressures less than 15 pounds per square inch gauge (psig) (103.4 kPa).
- Constantly attended.
- Provided with emergency shutoff valves that have ready access.