While significant incidents involving natural gas are rare and natural gas pipelines are statistically a safe form of transport compared to rail and motor vehicle transport of other fuels, natural gas can be dangerous. Gas is highly combustible when the proper air-to-fuel ratio exists, and natural gas can cause explosions when it is trapped in a confined space. Thus, responding to emergencies in order to protect life and property is the highest priority for gas company operations and maintenance personnel.
Emergency response is planned and implemented based on the following principles:
- Response to any suspected leaks should be immediate so that the flow of gas can be stopped before a source of ignition causes a fire or before concentrations of gas can collect in confined spaces.
- Specific protocols for safely responding to and resolving situations while protecting human life and property are developed ahead of time and are routinely reviewed and practiced.
- Gas control and engineering must be prepared to support field crews in shutting down affected portions of the network.
- After the emergency has been resolved, more support is required as the focus shifts to restoration of service for customers whose gas supply was shut down.
- Once service is restored and permanent repairs have been made, the last step is to study what happened to determine the cause and whether new procedures can be implemented cost effectively to prevent the situation from occurring again.
Here is an overview of steps a gas crew would take in responding to a significant leak report:
1. Assess the situation and take action to remove individuals from danger: As the crew reaches the site, they must determine the actions required to remove everyone from potential danger and to secure the site. Here is an example of actions:
- Use smell and gas detection equipment to determine whether a leak is present and, is so, how large the leak is
- Assess wind conditions to determine whether leaking gas will move to adjacent properties
- Immediately eliminate any sources of ignition
- Determine if gas is inside any buildings
- Immediately evacuate buildings when needed
- Ask for help from fire and police personnel on scene for clearing non-authorized personnel from the site and preventing others from entering
- Check basements and crawl spaces for the presence of gas
- Take all safety actions even if uncertain whether they are needed, it is better to be safe than sorry!
2. Stop the flow of gas: Once the site is secure, the next concern is to stop the flow of gas. If the leak is in the building it can be shutoff at the meter. Otherwise, it will be necessary to close a valve on the distribution or transmission system. Once the flow of gas has been stopped, it may take some time for the remaining gas in the line to clear either through venting or by combustion.
If possible, stop the flow of gas at or near the scene:
- Close the valve at the meter for leaks inside a building
- Close the street valve is one has been installed
- Squeeze plastic or steel distribution pipes upstream of the leak using a squeeze-off tool
If it is not possible to stop flow locally, then the crew must work with gas control and/or engineering to identify the most effective way to stop gas flow into that section of the system. This will result in multiple customer outages, so while it will be done to ensure safety, it must be done with careful thought.
- Close distribution valves or adjust settings on distribution regulator stations to block flow
- Close transmission valves
3. Restore service: Once the emergency has been addressed, the next concern is to restore service to affected customers. This may require pipe or other equipment repairs.
- If possible, pipe can be quickly repaired using devices such as clamps, sleeves, or plug valves
- If not possible to use such devices, damaged pipe must be replaced which will take more time
- After a repair is performed, the pipe must be tested for safety
- Then gas flow into the section can be restored
- Lastly, gas service representatives must visit each affected customer to ensure it is safe to restore service into their building and to relight pilot lights
4. Incident analysis: Once service has been restored to all customers, the final task is to work with a gas operations and engineering team to identify why the incident occurred and how effectively the response was performed. The team will then consider whether any design or operational procedure changes are warranted.