DUDEK - Los Angeles Methane Codes

After a methane gas explosion ripped apart a Los Angeles department store and injured 23 people, Los Angeles implemented an ordinance requiring methane mitigation for building in the neighborhood.

As more methane was discovered throughout the city, the methane code was expanded in 2004 to cover more regions and add more extensive mitigation technologies for construction, including formerly unaffected properties.

“The first time builders hear about these new regulations is usually when they pull their permit,” said Derek Reed, Dudek senior engineer. “Methane mitigation requirements catch them off guard with extra costs they hadn’t accounted for, and the project can easily get off schedule.”

An Invisible Threat
Methane is an odorless, colorless, non-toxic, non-carcinogenic gas that is extremely flammable at certain concentrations. As the main component of natural gas, methane lurks under Los Angeles’ streets, generally associated with hydrocarbon deposits. Pavement prevents it from escaping into the atmosphere and can channel it to cracks in concrete foundations, where it can collect in underground rooms of buildings – a huge explosion risk.

A city work group conducted a detailed study of natural methane levels all over Los Angeles and created a map with two different zones of methane risk: the Methane Buffer Zone and a more stringent Methane Zone. The updated methane code includes these new risk areas and requires more modern mitigation methods. Now the Department of Building and Safety (DBS) can refuse to issue permits for buildings in these two zones unless contractors provide a detailed methane mitigation strategy.

Among the First to Comply
One of the first buildings to comply with the new code was a 13-story apartment complex called Eleven South, located at 11th Street and South Grand Avenue. Dudek started the mitigation process by determining the building was in the Methane Zone and began conducting the appropriate testing.

To ascertain which mitigation processes were needed, Reed and his team tested the site for methane concentration and pressure by putting vapor wells in the ground and collecting data over three days.

Although no methane was detected, engineering controls to prevent methane intrusion still needed to be worked into the building design. “Seismic activity in LA could provide opportunities for methane to migrate through fractures in the future,” said Trey Driscoll, a Dudek geologist.

Methane Chimneys and Waterproof Membranes
Methane engineers began work with the architect to design mitigation plans for Eleven South. A four-inch-diameter perforated pipe in a shallow trench and wrapped with gravel was installed beneath the entire building. The pipe collects methane and pipes it up through the building, much as a chimney, venting the gas outside. The basement floor was sprayed with an impervious membrane that cures on the wall, essentially like a water proofing membrane, further preventing any gas intrusion into the building.

These extra mitigation steps extend the construction schedule, requiring close interaction with the contractor and the construction trades. Project success depends upon the methane mitigation professionals interacting with other trades, identifying problems early and scheduling mitigation installation at the most efficient time.

“We had a five-day window for the methane crew to get in and get out and do their testing,” added Fred DeFalco, senior superintendent at Howard S. Wright Construction Co., builders on the project. “Dudek was excellent about being here when we needed them.”

What’s Your Zone?
Huge blocks of property all over Los Angeles are subject to new methane mitigation standards. The higher risk Methane Zone is surrounded by the lesser risk Methane Buffer Zone, and patches of both can be found almost everywhere in the city.

If a new building is located within the Methane Buffer Zone:

Site testing is required to determine methane concentration and pressure.
If methane pressure is greater than two inches of water pressure, mitigation systems must be installed as described in Table 71 of the Methane Code.
If methane pressure is less than or equal to two inches of water pressure and methane concentration is 1000ppmv or less, no mitigation system is required.

If a new building is located within the Methane Zone:

Site testing is required to determine methane concentration and pressure.
Based on methane concentration and pressure, Table 71 describes the relevant mitigation systems.

See the code for certain exceptions. If the Department of Building and Safety (DBS) determines that a hazard exists from methane intrusion in a property outside the Methane Zone and Methane Buffer Zone, DBS and the Fire Department may enforce methane mitigation standards. Additionally, existing buildings and paved areas must also comply with the new regulations in certain instances.

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