1 Find a radionuclide
Values are shown exactly as printed in Appendix B Table 1. A dash (—) means the table gives no value for that cell. Parentheses give the stochastic ALI under the organ named above it.
2 DAC unit converter
1 µCi = 3.7×10⁴ Bq and 1 mL = 10⁻⁶ m³, so 1 µCi/mL = 3.7×10¹⁰ Bq/m³.
3 DAC fraction & DAC-hours
DAC-hours = (concentration ÷ DAC) × hours. 2,000 DAC-hours = 1 inhalation ALI ≈ 5 rem (0.05 Sv) CEDE on the stochastic basis, so 1 DAC-hour ≈ 2.5 mrem. Tip: click a row in the results table to load its DAC here.
4 ALI unit converter
1 µCi = 3.7×10⁴ Bq = 0.037 MBq.
| Radionuclide | Class | Oral ALI (µCi) | Inhalation ALI (µCi) | DAC (µCi/mL) | DAC (Bq/m³) |
|---|
Working to keep airborne concentrations at a small fraction of DAC is what nuclear air cleaning is sized and tested for — see the IAS-NC700-HI and IAS-NC500-HI-CUSTOM HEPA + iodine adsorber units, the air purification sizing calculator, and our custom iodine adsorption systems.
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What the DAC and ALI mean
ALI — Annual Limit on Intake. The ALI is the amount of one radionuclide, in microcuries (µCi), that a worker may take into the body in a year before reaching the dose limits behind 10 CFR 20.1201: the smaller of 5 rem (0.05 Sv) committed effective dose equivalent (the stochastic basis) or 50 rem (0.5 Sv) committed dose equivalent to any single organ or tissue (the non-stochastic basis). Table 1 prints an oral (ingestion) ALI and an inhalation ALI for each radionuclide. Where an organ value governs, the table names the organ and prints the stochastic ALI in parentheses beneath it.
DAC — Derived Air Concentration. The DAC turns the inhalation ALI into an air concentration. It assumes reference man breathing at 2×10⁴ mL/min (1.2×10⁶ mL per hour) for a 2,000-hour working year, so the volume breathed is 2.4×10⁹ mL:
DAC-hours. Real exposures are tracked as the sum of (concentration as a fraction of the DAC) × hours. Breathing air at exactly 1 DAC for 2,000 hours gives an intake of 1 ALI — 2,000 DAC-hours — equal to 5 rem CEDE on the stochastic basis, so each DAC-hour is about 2.5 mrem. Internal dose is assessed from DAC-hour records (or bioassay) under 10 CFR 20.1203, and the sum of external deep dose and internal committed dose must stay within the 5 rem total effective dose equivalent limit of 10 CFR 20.1201.
Classes D, W, Y. Inhalation values depend on how fast the inhaled material clears from the lung: class D (days), W (weeks) or Y (years). Many Table 1 entries name a chemical form instead (oxides, fluorides, elemental vapour, and so on) or combine a class with named exceptions — the class column here reproduces the table's wording, including its "see" cross-references to the isotope whose compound list applies. Submersion entries (noble gases and similar) give a DAC based on external dose from the cloud, marked with the table's submersion footnote.
Unit conversions used by this tool
Questions
What is a DAC (derived air concentration)?
The DAC is the concentration of a radionuclide in air that, if breathed by reference man for 2,000 working hours in a year (at the reference breathing rate of 2×10⁴ mL per minute), results in an intake of one ALI — the dose basis of the annual limits in 10 CFR 20.1201. DAC values are tabulated in 10 CFR 20 Appendix B, Table 1, in µCi/mL.
What is an ALI (annual limit on intake)?
The ALI is the amount of a radionuclide, in microcuries, taken into the body by ingestion or inhalation in a year that delivers the limiting dose: 5 rem (0.05 Sv) committed effective dose equivalent on the stochastic basis, or 50 rem (0.5 Sv) committed dose equivalent to any individual organ or tissue on the non-stochastic basis, whichever is smaller. Appendix B Table 1 lists an oral ALI and an inhalation ALI for each radionuclide and class.
How many DAC-hours equal the annual dose limit?
2,000 DAC-hours. Exposure at a concentration of 1 DAC for 2,000 hours is an intake of 1 inhalation ALI, equal to 5 rem (0.05 Sv) committed effective dose equivalent on the stochastic basis, so 1 DAC-hour corresponds to about 2.5 mrem. Facilities track DAC-hours (concentration as a fraction of DAC, multiplied by hours) to assess internal dose under 10 CFR 20.1203.
How do I convert a DAC from µCi/mL to Bq/m³?
Multiply by 3.7×10¹⁰. One microcurie is 3.7×10⁴ becquerels and one millilitre is 10⁻⁶ m³, so 1 µCi/mL = 3.7×10⁴ Bq per 10⁻⁶ m³ = 3.7×10¹⁰ Bq/m³. Example: the I-131 class D DAC of 2E-8 µCi/mL equals 740 Bq/m³.
Which class (D, W or Y) should I use?
Use the class printed in Appendix B Table 1 for the chemical form of the material: D, W and Y are the lung clearance classes (days, weeks, years) used in the table, and many entries instead name a specific form such as oxides, fluorides or elemental vapour. The class changes the inhalation ALI and DAC, sometimes by orders of magnitude. If the form is not known, the choice is a radiation-protection decision — confirm with your RSO and licence conditions.
Where do these DAC and ALI values come from, and can I rely on them for compliance?
The values are those published by the U.S. Nuclear Regulatory Commission in 10 CFR Part 20, Appendix B, Table 1. This page is a reference copy for planning and training. Regulations are amended from time to time, so verify the values against the current CFR (eCFR) and your facility's licence and RSO before any compliance decision.