All fire departments respond to natural-gas line cuts, leaks and ruptures throughout the year. In most cases, workers hit the lines, even though the lines previously have been located and marked by the local service companies. Usually, the incident is caused by

1. A car runs that into a gas meter;
   


2. Construction work, usually a backhoe or other earth-mover, that clips a line in an open ditch; or,
   


3. A boring machine (boring under concrete or asphalt) that hits a line.
   

Because such a large percentage of natural gas delivered in the United States is composed of methane with a vapor density of 0.55 (some texts round up to 0.6), the worst of the hazard dissipates into the atmosphere. The hazard zone around the leaking natural-gas line is relatively small, and the real danger of the situation is small as long as we keep ignition sources out of the area of vapor that is within its flammable limits. It’s a little different if a boring machine cuts a line underground but the known conflict, or gas line, has not been opened. This is called potholing, or localized hole drilling. If everyone operator using a boring machine consistently potholed the line conflicts, it would seldom be a big deal.

On May 16 in McKinney, a company boring to install new gas distribution lines drilled through a 3-inch natural-gas line because they had not potholed the conflict. The facts of this case eventually will be fought out in the courts, but I am writing this now because of the imminent hazard that is created when boring operations occur without potholing conflicts.

The line was ruptured at about 4:30 p.m. Work was stopped and the subcontractor and the gas utility company were notified. The fire department, however, was not called. We are told that the industry standard of natural-gas utility companies does not include reporting the leak to the fire department. At about 5:39 p.m., the 911 dispatch center received reports of houses exploding and burning. This was our first notification of the problem. Even though numerous people in the area smelled the gas leaking, no one called us.

We clearly need to do a better job is public education.

Two houses exploded at nearly the same time and were collapsed and fully involved when we arrived at 5:43 p.m. Three people were inside of the two houses and were severely burned. At 5:46 p.m., while fire crews were deploying master streams, the house right next to the gas leak exploded.

Fortunately the firefighters weren’t injured by the flying glass or collapsing structure. The captain of the crew deploying lines told me that it got their attention. The third house was a duplex built as a slab-on-grade, while the two houses to the west of this structure were

had pier-and-beam foundations.

Natural gas leaking under ground with no open pit to allow the methane to escape will find the path of least resistance to relieve the pressure. In this case an abandoned sewer line is the suspected conduit.

It’s important to understand the notification policies of local gas utility companies for an ongoing gas leak. We will certainly respond to many more reported gas leaks because our local gas utility now will report all gas line cuts and leaks to the 911 center. But this gives us the opportunity to take appropriate actions to protect residents. In most cases, we simply stand by until the repair crew arrives if we arrive first — and it seems to me that we should arrive first.

Occasionally we decide to move exposed people out of a danger zone, which we determine using the meters carried by our engine and truck companies. Our choice is to stay on the side of safety and not expose people to real or perceived risk.

Understand that the methyl mercaptan used an the odorant in most natural gas has a vapor density of 1.7. The second most common component of natural gas by volume is normally ethane, which has a vapor density just slightly greater than air at 68°F. It’s hot in Texas this time of year, so even the ethane dissipates rapidly when leaking from a line cut in an open pit.

My message to the media continues to be that everyone who smells leaking natural gas should call 911 immediately and not assume someone else has. The outcome of this recent incident would have been different had we been called early. Logically, as I’ve told our residents in McKinney, we have a response time of about six minutes after an emergency is reported to 911. If we’re not showing up in about that time, we probably haven’t been called. Don’t assume someone else has called to report an emergency.