Police and fire departments frequently receive reports of a natural gas odor from an unknown source. It can be frustrating to identify and mitigate the source of the odor, as reports often come from multiple points within an area and witness accounts often vary. Sometimes, reports come from the same area repeatedly and the odor dissipates without a source being identified. The consequences of a natural gas leak can be grave, so it is essential that you fully investigate any report of a gas odor as a potentially dangerous natural gas leak.

Natural gas is colorless and odorless, so Mercaptan, an odorant, is added to give natural gas its rotten-egg smell. Be aware that, although this odor often aids in detection of natural gas leaks, you may not be able to smell Mercaptan if you have been exposed to it for too long or if it is masked by other odors. Mercaptan may also be stripped from the gas due to chemical and physical processes. It may be filtered out by sand or gravel, or it may smell like something else when mixed with other substances in air. In addition, several substances may smell like Mercaptan, including sewer gas, decomposing proteins or chemicals improperly released into the atmosphere or sewer system.

For all these reasons, never rely on your nose alone to determine whether a gas leak exists. You must use combustible gas indicators (CGI) to be certain whether dangerous levels of natural gas are present.

Response tactics

Upon receiving a report of a gas leak, your dispatcher should advise callers to evacuate the immediate area but remain on scene to provide the arriving fire officer with specific information. The dispatcher should initiate a public safety response to isolate and investigate the incident and then notify National Grid or the local natural gas utility and request an immediate response. In addition, the dispatcher should notify other municipal and public safety agencies, including the police department and possibly the Department of Public Works (DPW).

Police and fire personnel should approach the incident scene cautiously. Stage vehicles upwind, away from the hazard area at a safe distance. If a leak is confirmed, a staging distance of 330 feet is recommended, if possible. Park safely out of the collapse zone of involved structures, and away from manhole covers, gas valve covers and storm sewer grates.

Upon arrival, interview the reporting parties to obtain as much information as possible. Law enforcement personnel should evacuate the immediate area (100 feet) and reroute traffic away from your immediate operating area to minimize ignition sources and create an appropriate exclusion zone. If reports of gas odors recur in a specific area, never assume that the same situation exists because that’s what happened last time: Conduct interviews and evacuate each and every time.

Personnel in full Personal Protective Equipment (PPE) and Self-Contained Breathing Apparatus (SCBA) should initiate air monitoring of the area and determine an appropriate exclusion zone that will ensure the safety of the public and provide a sufficient operating area for fire service personnel.