What is Methane Mitigation?

Here’s the updated article with a clear structure addressing all key questions: — If a new construction project is located within a Methane Zone, the Los Angeles Department of Building and Safety will require a Methane Test. Based on the Methane Test results, the property will be classified as Methane Levels 1 through 5. Each Methane Level has corresponding mitigation requirements that need to be implemented in the methane mitigation design and construction.  

What is the Methane Mitigation Process?

The Methane Mitigation Process is an environmental engineering procedure that protects buildings from methane gas intrusion. It requires certification by the Los Angeles Department of Building and Safety (LADBS) for any construction project located within a Methane Zone. The process includes three key components: testing the soil for methane levels, designing a mitigation system based on test results, and constructing that system according to LADBS specifications. Once installed, the system prevents methane gas from entering the building through the foundation.

Why Do You Need Methane Mitigation?

Methane gas poses serious safety risks when it accumulates inside buildings. It’s combustible, which means it can ignite and cause explosions. Beyond the fire hazard, methane can displace oxygen in enclosed spaces, creating health risks for building occupants. The LADBS Methane Code exists because certain areas of Los Angeles sit above oil fields and other geological formations that naturally release methane. If you’re building in one of these zones, mitigation isn’t optional. The city won’t issue permits without proper methane testing and mitigation systems in place. Properties receive a classification of Methane Levels 1 through 5 based on Methane Test results. Higher levels indicate greater gas concentrations and require more stringent protective measures.

What’s the Methane Mitigation Process?

The process follows a specific sequence mandated by LADBS: Step 1: Methane Testing (LADBS Methane Soil Test) Environmental engineers drill test holes on your property to measure methane gas concentrations and flow rates in the soil. These tests determine your property’s Methane Level classification. Testing must be conducted by licensed professionals who submit results directly to LADBS. Step 2: Methane Mitigation Design Based on your test results, licensed engineers create plans for your mitigation system. The design specifies which protective measures you need, such as vapor barriers, ventilation systems, or gas detection equipment. Plans must comply with LADBS Methane Code requirements for your specific Methane Level. Step 3: Methane Mitigation Construction Specialty contractors install the designed system during your building’s construction. This typically includes sub-slab ventilation systems, methane barriers beneath the foundation, and sometimes active venting equipment. Installation happens in coordination with your general contractor’s schedule. Step 4: Methane Deputy Inspection LADBS inspectors verify that your system was built according to approved plans. They check that all components are properly installed and functioning. You can’t receive a certificate of occupancy until this inspection passes.

How Much Does Methane Mitigation Cost?

Costs vary significantly based on your property’s Methane Level classification and building size. A Level 1 or 2 site might only need basic passive barriers, which cost less. Level 4 or 5 sites require active ventilation systems with ongoing monitoring, which increases both installation and maintenance expenses. Testing alone typically runs several thousand dollars. Design fees depend on project complexity. Construction costs can range from tens of thousands to over $100,000 for larger commercial buildings with high methane levels. Your specific costs depend on: – Property size and building footprint – Methane Level classification (1-5) – Soil conditions and site accessibility – Whether you need passive or active systems – Local contractor availability and rates

The methane mitigation process can have a varying cost. Learn more about the most common questions and the answers to Methane Mitigation.

You will learn more about the Methane Mitigation process and the LADBS Methane Soil Test in congruence to the LADBS Methane Code. The Los Angeles Department Of Building And Safety: “A permit from LADBS is required for any private property construction, alteration, or repair work on buildings within the City of Los Angeles.”

Why do I need a Methane Vapor Mitigation System?

Methane Mitigation Systems include a series of redundant design approaches. To prevent the migration of gas vapors into the interior space of a structure. One of the main components of Methane Vapor Systems is the Methane Gas Vapor Barrier.  This Methane Membrane is installed below the foundation of a system and acts as a seal for the concrete slab, which requires a Vapor Mitigation Contractor.

Why can’t my concrete slab prevent methane vapor migration? 

Any vapor, depending on the size of the molecule, can diffuse through a surface. Diffusion is the movement of a substance through a character, typically driven by pressure and concentration gradients. A relatable example would be a helium balloon deflating over some time.  The helium pressure and concentration are significantly higher than in the atmosphere, and the size of helium molecules is tiny.  So, naturally, the helium wants to migrate through the balloon’s surface to reach the atmosphere.  Over time, helium finds its way through the tiny crevasses of the balloon material. Ultimately, most helium diffuses, resulting in balloon deflation. This phenomenon goes by the term Mass Diffusion.  The same concept of mass diffusion of helium through a balloon is applied to Methane Gas through a concrete slab, besides the fact that concrete slabs can have cracks which are open pathways for gas vapors.  Over time, the methane gas can diffuse through the concrete slab introducing explosion risks inside a structure.

Methane Mitigation Designers implement a material installed beneath a structure’s foundation.

This material is designed to reduce the diffusion of methane gas vapor.  The reduction of scattering is driven by several variables, including Methane Gas Vapor Pressure (Industry standard Measures in Inches of Water), Methane Gas Construction, typically measured in parts per million (PPMV), Methane Barrier Material, and Vapor Barrier Thickness. Referring to the helium balloon example, if the balloon membrane was thicker, it may reduce the diffusion rate accordingly. Also, if a different material was in use, it may reduce the helium Gas Migration.  Similarly, Methane Barriers design is to distinctly minimize the diffusion rates of methane gas.  The thickness of the barrier can change accordingly for projects and anticipated risks.  This proves that not all methane barriers have the same diffusion prevention capabilities.

Vapor Gas Migration Engineering Comparison

Methane Mitigation aligns with the study of heat transfer and the thermal sciences. The term used to measure to diffusion capability of a material is termed the coefficient of Mass diffusion. Mass Diffusion values can be calculated using Fick’s Law. Which has a close analysis methodology to Fourier’s Law of Conduction for Heat Transfer. What values of mass diffusion are appropriate for use? The Los Angeles building and safety and the DTSC have established safety values for Mass Diffusion through Methane Barrier.  All approved Methane Barriers need to meet the standards to ensure they can sufficiently prevent methane diffusion at a reasonable rate. This is why a Vapor Mitigation Contractor is required. This ideology and theory are only appropriate if you have a perfectly sealed foundation to the sub-surface. For this reason, it is essential to emphasize that a licensed Methane Mitigation Contractor must install vapor mitigation systems to ensure the foundation’s seal is perfect. Any loose ends, holes, or obstructions can create a path for methane to intrude into a building without the protection of the Methane Barrier.

Sub Slab Depressurization System

  The sub-slab vent system is another redundant methane mitigation design approach which implements in Methane Mitigation Construction.  As previously noted, Mass Diffusion is not only a function of concentration differential but also a function of pressure differential. The larger the pressure and concentration gradients, the higher the mass diffusion. This is where the sub-slab vent system comes to help. Implementing a sub-slab vent system allows the depressurization of the subfloor to ensure that the pressure differentials are minimal; this reduces the mass diffusion and also introduces relief in the case of an obstruction on the membrane. The Sub slab vent system allows the methane gas to route through vents rather than through the structure. Methane vent pipes consist of perforated pipe along with a gravel blanket below the surface of a building. These systems design in mind by a licensed professional engineer with experience in designing methane depressurization vent systems.

Vapor Mitigation Design

  The details utilized prepared on the Vapor Mitigation Design is of utmost importance; often time consultants use standard components that manufacturers or city officials prepare.  This poor practice leads to issues during construction for lacking details and direction during the Vapor Mitigation Construction phase.

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