Short answer: Under 40 CFR 370.14, the amount of a hazardous chemical in a mixture is its weight percent multiplied by the weight of the mixture in pounds. For an Extremely Hazardous Substance (EHS), you must add the EHS content of every mixture on site to any pure EHS to test the threshold. For other hazardous chemicals, you may total either the component across all mixtures or the mixture as a whole. Components at or below 1%, or at or below 0.1% for carcinogens, do not have to be counted. When the SDS gives only a range, EPA’s guidance is to use the upper bound.
Two separate questions: threshold and reporting
Section 370.14 answers two questions for each mixture. First, how do you decide whether a threshold has been met? Second, once it has, what do you report: the component or the mixture? The answer depends on whether the hazardous chemical is an EHS.
| Component type | How to test the threshold | What you may report |
|---|---|---|
| EHS | Total the EHS across the facility at any one time: the EHS in every mixture plus all other quantities of the EHS. Count the EHS in a mixture even if you also count that mixture toward its own threshold. | Either the EHS component, or the mixture itself with the mixture’s total quantity. |
| Non-EHS hazardous chemical | Either total the component across all mixtures and other quantities, or total the quantity of that mixture present at any one time. | Either the component, or the mixture itself with the mixture’s total quantity. |
The practical consequence: for an EHS you cannot avoid component-level arithmetic. A site with five products that each contain a little of the same EHS may cross 500 pounds of that EHS even though no single product is near any threshold. For non-EHS chemicals you have a choice, and the mixture-as-a-whole method is often simpler where the components are not well characterized. EPA’s guidance adds that when a mixture’s composition is unknown, you should report the mixture as a whole using its total quantity.
What 370.14 says about concentration
The regulation’s text on concentration is short. Paragraph (c) reads in full:
40 CFR 370.14(c)
“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). You do not have to count a hazardous chemical present in a mixture if the concentration is less than or equal to 1%, or less than or equal to 0.1% for a carcinogenic chemical.” (40 CFR 370.14(c))
Three things follow directly from that text. The concentration is in weight percent, so a volume percent from an SDS has to be converted, or the mixture weighed, before it is used. The weight of the mixture is in pounds, so liquids in gallons have to be converted first (see gallons to pounds). And the cut-off is “less than or equal to” 1%, so a component listed at exactly 1% does not have to be counted.
The regulation does not say what to do when the SDS gives a range instead of a single number. That is where guidance and practice come in.
SDS concentration ranges: regulation, guidance, and practice
Section 3 of an SDS for a mixture lists each classified ingredient with its concentration. OSHA’s Hazard Communication Standard requires the exact percentage unless a trade secret claim is made or there is batch-to-batch variability, in which case a range may be used. When the concentration itself is claimed as a trade secret, the SDS must use one of thirteen prescribed ranges, such as 10% to 30% or 30% to 60%, and the narrowest one that fits (29 CFR 1910.1200(i)(1)(iv)–(v)). Wide ranges are common.
It helps to keep three layers separate:
- Regulation. 40 CFR 370.14(c) says to multiply weight percent by mixture weight. It is silent on ranges.
- EPA guidance. EPA’s published answer on reporting an EHS mixture from a concentration range says: “If the MSDS for the mixture indicates only a range of concentration for its components, then for purposes of reporting under Sections 302, 304, and 311/312 of EPCRA, the facility owner/operator should use the upper bound concentration when determining the weight of each component in the mixture.” EPA’s stated reason is that this is consistent with EPCRA’s purpose of maximizing communities’ opportunity to know about local chemicals. The question was posed about EHS mixtures, but the answer as written covers components in general under §§302, 304, and 311/312.
- Practice (our recommendation, not a rule). Apply the upper bound to every component for threshold checks, record the full range alongside it, and note which SDS revision the range came from. If the supplier will give you an exact or narrower concentration in writing, use that and keep the letter with the calculation.
For comparison, the TRI rules for §313 do address this in regulation: where a facility knows only the upper bound concentration of a toxic chemical in a mixture, it must assume the chemical is present at that upper bound (40 CFR 372.30(b)(3)(ii)). That rule governs TRI, not Tier II, but it points in the same direction.
Ranges also interact with the 1% cut-off. A component listed at 0.1% to 1% has an upper bound of 1%, which is “less than or equal to 1%,” so it can be left out (unless it is a carcinogen). A component listed at 0.5% to 1.5% has an upper bound above 1%, and under the upper-bound approach it is counted.
Worked example: one CAS number across three products
A site holds three products that each contain sulfuric acid (CAS 7664-93-9). Sulfuric acid is an EHS with a TPQ of 1,000 lb (40 CFR Part 355, Appendix A), so its Tier II threshold is the lower of 500 lb and 1,000 lb: 500 lb. As an EHS, it must be totaled across all three products. The quantities below are the largest amounts of each product on site on the same day.
Product A, concentrated acid, SDS range 93–98%, 250 lb on hand. Upper bound: 250 × 0.98 = 245.0 lb.
Product B, descaler, SDS range 10–30%, 600 lb on hand. Upper bound: 600 × 0.30 = 180.0 lb.
Product C, pH adjuster, SDS range 30–60%, 400 lb on hand. Upper bound: 400 × 0.60 = 240.0 lb.
Total at the upper bound: 245.0 + 180.0 + 240.0 = 665.0 lb. That is at or above 500 lb, so sulfuric acid is reportable on Tier II. At the lower bound the total would be 232.5 + 60.0 + 120.0 = 412.5 lb, below the threshold. The choice of bound decides the outcome here, which is why it should be written down. The 665-lb total is still below the 1,000-lb TPQ, so this inventory alone does not trigger the EPCRA §302 notice.
Three cautions on the example. The quantities must be on site at the same time; a product that was used up in March and a product that arrived in June are not added together. The concentrations must be weight percent; acid strengths are usually given that way, but check the SDS. And if you report the mixture itself for any of these products, Tier II still asks for the amount of each EHS within that mixture (40 CFR 370.42(s)(6)).
Report each mixture the same way in §311 and §312
For each specific mixture, the option you choose must be consistent between §311 SDS reporting and §312 inventory reporting, unless that is not possible (40 CFR 370.14(b)). If you submitted the SDS for a product as a whole under §311, report that product as a whole on Tier II. If you listed the component under §311, report the component. See EPCRA 311 notification for the one-time submission.
How a mixture appears on the Tier II form
When you report a mixture, 40 CFR 370.42(s) requires the mixture or product name and the CAS number shown on the SDS, with a “Not Available” box if there is none. If the mixture contains any EHS, you must name each EHS and give the total amount of each EHS in the mixture. Reporting non-EHS components of the mixture is optional. The maximum and average daily amounts are for the mixture as a whole.
The same arithmetic applies to EPCRA §302
For the emergency planning threshold, Part 355 uses the same method: multiply weight percent by the weight of the mixture in each container, add the EHS in all mixtures to any pure EHS regardless of location or container, and skip an EHS present at or below 1% (40 CFR 355.13 and 355.14). Part 355 does not have the separate 0.1% carcinogen cut-off that Part 370 has. The TPQ test is covered in EPCRA 302 EHS and TPQs.
Common questions
Do I report the mixture or each hazardous component on Tier II?
Either is allowed under 40 CFR 370.14. You may report the hazardous component or the mixture itself. If the mixture contains an EHS, you must still determine the total EHS across the facility to test the threshold, and the Tier II form asks for the amount of each EHS in the mixture. Use the same option for the mixture in your EPCRA 311 submission.
Should I use the high or low end of an SDS concentration range?
EPA’s published guidance says to use the upper bound concentration when an SDS gives only a range, for reporting under EPCRA sections 302, 304, and 311/312. The regulation itself, 40 CFR 370.14(c), only says to multiply weight percent by mixture weight.
What is the de minimis concentration for Tier II mixtures?
A hazardous chemical at or below 1% of a mixture, or at or below 0.1% for a carcinogen, does not have to be counted (40 CFR 370.14(c)).
How do I calculate the amount of a chemical in a mixture?
Multiply the component’s concentration in weight percent by the weight of the mixture in pounds. For 600 pounds of a product containing 30% of a chemical by weight, the chemical content is 180 pounds. Convert gallons to pounds before applying the percentage.
Do I add the same chemical across different products?
For an Extremely Hazardous Substance, yes: the EHS in every mixture is added to any pure EHS on site. For other hazardous chemicals, you may either total the component across all products or apply the threshold to each mixture as a whole (40 CFR 370.14(a)).
Where Chemsana fits
Chemsana extracts composition from Section 3 of each SDS and keeps inventory as a ledger totaled by CAS number across products, with low, nominal, and high bounds. Threshold checks use the upper bound, and the math is shown with the citation. See how inventory totals work.
Sources
- 40 CFR 370.14, How do I report mixtures containing hazardous chemicals?, eCFR, accessed October 2026.
- 40 CFR 370.42, Tier II inventory information, eCFR, accessed October 2026.
- 40 CFR 355.13 and 355.14, EHS in mixtures and aggregation, eCFR, accessed October 2026.
- 40 CFR Part 355, Appendix A (sulfuric acid TPQ), eCFR, accessed October 2026.
- 29 CFR 1910.1200(i), trade secrets and prescribed concentration ranges, eCFR, accessed October 2026.
- 29 CFR 1910.1200 Appendix D, Safety Data Sheets, OSHA, accessed October 2026.
- 40 CFR 372.30(b)(3), TRI mixtures and upper bound concentration, eCFR, accessed October 2026.
- Reporting for an EHS mixture based on a concentration range, EPA frequent question, accessed October 2026.
- How are mixtures handled for Sections 311 and 312 reporting?, EPA frequent question, accessed October 2026.
This guide summarizes federal requirements for general information. States can set lower thresholds or extra requirements, and it is not legal advice. Confirm obligations with your SERC, LEPC, or a qualified EHS professional.