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Biogas and Human Health

California Legislative Assembly Bill 1900 (AB 1900, Statutes of 2012, Chapter 602) requires the California Public Utilities Commission (CPUC) to develop standards for certain constituents found in biogas. This is done to protect human health and ensure pipeline safety. Once biogas meets the standards, it is then considered to be biomethane that may be injected into utilities’ natural gas distribution systems. In support of the rulemaking process, the Office of Environmental Health Hazard Assessment (OEHHA) and the California Air Resources Board (CARB) are mandated to perform specific tasks and provide recommendations to the CPUC:

  • OEHHA, in consultation with CARB and others, compiles a list of constituents of concern. These are chemicals present in biogas at levels substantially higher than found in natural gas. Constituents of concern could pose a health risk to consumers, workers, or other members of the public. 
  • OEHHA determines health-protective levels for the constituents of concern.
  • CARB identifies realistic exposure scenarios for biogas.
  • CARB and OEHHA use the exposure scenarios and the health-protective values for chemicals of concern to identify potential health risks associated exposure. Health-protective concentrations are determined for the constituents of concern in biogas.
  • CARB, in consultation with other CalEPA boards and departments, defines monitoring and reporting requirements to ensure that health-protective levels will be maintained.
  • CARB and OEHHA are required to update their recommendations at least every five years.

The CARB-OEHHA joint recommendations document, “Recommendations to the California Public Utilities Commission Regarding Health Protective Standards for the Injection of Biomethane into the Common Carrier Pipeline,” was finalized and submitted to the CPUC on May 15, 2013.

In 2020, OEHHA updated recommendations for biomethane trace-constituent concentration limits. In 2023, CARB finalized and submitted its recommendations. These documents together make up the first review of the 2013 report.

First Updated Recommendations for Biogas

The CARB report, “Biogas Constituents of Concern and Health Protective Levels for Biomethane: Supplement Report to OEHHA AB 1900 Biogas Recommendations” was finalized and submitted on April 24, 2023. This report along with OEHHA’s 2020 report, “AB 1900 Biogas Recommendations” fulfills AB1900’s requirement to update biogas recommendations every five years. The reports include:

  • Revised list of constituents of concern.
  • Recommendations for health-protective levels of constituents of concern.
  • Updated source categories.
  • Updated toxicity criteria and risk calculations.
  • Updated CARB’s 2013 residential indoor-air exposure models, including a combustion scenario based on the use of a biogas-fueled kitchen stove.
  • Revised concentrations used for risk management, which are based on updated risk values.
  • Updated recommended testing methods.
  • Updated reporting and recordkeeping requirements.

The AB 1900 update reports and associated documents are provided via the following links:

  • Transmittal Memo from CARB staff, dated April 24, 2023
  • CARB Report: “Biogas Constituents of Concern and Health Protective Levels for Biomethane: Supplement Report to OEHHA AB 1900 Biogas Recommendations” and Appendix A
  • OEHHA 2020 Report: “Biogas Constituents of Concern and Health-Protective Levels for Biomethane”

In addition, an Excel-based Constituents of Concern Health Risk Calculator is available upon request.

The 2013 CARB-OEHHA report and associated documents and data are provided via the following links:

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