• To determine the quantity of an EHS or a non-EHS hazardous chemical component present in a mixture, multiply the concentration of the hazardous chemical component by the weight of the mixture.
• In order to reduce the regulatory burden on facilities, EPA promulgated a de minimis exemption for Tier I (or Tier II) reporting.

A mixture is a combination of two or more different substances, each retaining its own chemical identity. Facilities may have mixtures containing extremely hazardous substances (EHSs) or hazardous chemicals. To determine the quantity of an EHS or a non-EHS hazardous chemical component present in a mixture, multiply the concentration of the hazardous chemical component (in weight percent) by the weight of the mixture (in pounds).

However, the owner or operator of a facility can choose to report all the components of a mixture separately or report the mixture as a whole (e.g., if the composition of a mixture is unknown), unless it is not possible to do so. The catch is whichever option the facility uses, the reporting of mixtures must be consistent for reporting under both EPCRA 311 and EPCRA 312, where practicable. If a facility reports on mixtures as a whole in EPCRA 311, it must do the same in EPCRA 312, where practicable. (EPCRA 311 is about SDS/MSDS reporting, and EPCRA 312 is about Tier I (or Tier II) reporting.)

EPA regulation 40 CFR 370.14 offers a handy table to explain the mixture requirements:

If the mixture contains a hazardous chemical	To determine if the threshold level for that hazardous chemical is equaled or exceeded, the facility owner or operator must:	If the threshold level for that hazardous chemical is exceeded, then the facility owner or operator must:
That is an EHS	Determine the total quantity of the EHS present throughout the facility at any one time, by adding together the quantity present as a component in all mixtures and all other quantities of the EHS (include the quantity present in a mixture even if the owner or operator is also counting the quantity of that particular mixture toward the threshold level for that mixture).	Report the EHS component—submit a material safety data sheet (MSDS) or safety data sheet (SDS) for the EHS (or include the EHS on the list of chemicals submitted in lieu of the MSDSs or SDSs), as provided under 370.30, and submit Tier I (or Tier II) information for the EHS, as provided under 370.40; OR Report the mixture itself—submit an MSDS or SDS for the mixture (or include the mixture on the list of chemicals submitted in lieu of the MSDSs or SDSs), as provided under 370.30, and submit Tier I (or Tier II) information for the mixture, as provided under 370.40. If the owner or operator reports the mixture itself, then provide the total quantity of that mixture.
That is not an EHS	Determine either: The total quantity of the hazardous chemical present throughout the facility at any one time by adding together the quantity present as a component in all mixtures and all other quantities of the hazardous chemical (include the quantity present in a mixture even if the owner or operator is also applying that particular mixture as a whole toward the threshold level for that mixture); OR The total quantity of that mixture present throughout the facility at any one time.	Report the non-EHS hazardous chemical component—submit an MSDS or SDS for the non-EHS hazardous chemical (or include the non-EHS on the list of chemicals submitted in lieu of the MSDSs or SDSs), as provided under 370.30, and submit Tier I (or Tier II) information for the non-EHS hazardous chemical as provided under 370.40; OR Report the mixture itself—submit an MSDS or SDS for the mixture (or include the mixture on the list of chemicals submitted in lieu of MSDSs or SDSs), as provided under 370.30, and submit Tier I (or Tier II) information for the mixture, as provided under 370.40. If the owner or operator reports the mixture itself, then provide the total quantity of that mixture.

In order to reduce the regulatory burden on facilities, EPA promulgated a de minimis exemption for SDS (or MSDS) and Tier I (or Tier II) reporting. The exemption found at 40 CFR 370.14(c) excludes facilities that have very small, or de minimis quantities of hazardous chemicals or EHSs in mixtures. Mixtures that contain hazardous chemicals or EHSs below the de minimis level need not be counted toward the threshold. There are two different de minimis levels established:

• 1 percent for noncarcinogens — If a hazardous chemical exists in concentrations of 1 percent or less by weight, it does not need to be counted in determining threshold applicability.
• 0.1 percent for carcinogens — If the chemical is a carcinogen, concentrations of 0.1 percent by weight or less are considered de minimis, and therefore do not need to be counted towards thresholds.