63.3.3.1.12 Emergency Isolation

Where compressed gases having a hazard ranking in one or more of the following hazard classes in accordance with NFPA 704 are carried in pressurized piping above a gauge pressure of 15 psi (103 kPa), an approved method of emergency isolation shall be provided:

1. Health hazard Class 3 or Class 4
2. Flammability Class 4
3. Instability Class 3 or Class 4

[55:7.3.1.12.1]

Approved means of meeting the requirements for emergency isolation shall include any of the following:

1. Automatic shutoff valves, located as close to the bulk source as practical, tied to leak detection systems
2. Attended control stations where trained personnel can monitor alarms or supervisory signals and can trigger emergency responses
3. A constantly monitored control station with an alarm and remote shut off of the gas supply system
4. Excess flow valves at the bulk source

[55:7.3.1.12.2]

The requirements of 63.3.3.1.12 shall not be required for the following:

1. Piping for inlet connections designed to prevent backflow at the source
2. Piping for pressure relief devices
3. Where the source of the gas is not in excess of the quantity threshold indicated in Table 63.2.3.1.1

[55:7.3.1.12.3]

The requirements of 63.3.3.1.12 shall not apply to the following:

1. Piping for inlet connections designed to prevent backflow
2. Piping for pressure relief devices
3. Systems containing 430 scf (12.7 m³) or less of flammable gas

[55:7.3.1.12.4]