What situation defines a major gas emergency?

A major gas emergency is characterized by the presence of gas in two or more subsurface structures, indicating a broader and potentially more dangerous situation. This scenario signifies that gas can migrate through the ground and affect multiple areas, which poses an increased risk of explosion, poisoning, or fire.

In contrast, while gas leaking from an appliance might indicate a serious issue, it is typically considered a localized problem that may not escalate to a major emergency unless it leads to a more widespread concern. Similarly, gas readings below 2% LEL (Lower Explosive Limit) are generally not considered dangerous or indicative of an emergency. Lastly, gas present in only one manhole, while it shows a potential issue, does not suggest widespread danger compared to the scenario where gas is found in multiple subsurface structures.

The presence of gas in multiple areas underscores the need for immediate and coordinated action to mitigate risks, making it a defining factor of a major gas emergency.