Target Levels for
Radiation Decontamination of People

Key Info:
key


  • Skin or wound contamination is rarely life threatening to either patients or medical personnel caring for them.
  • Removing outer clothing and shoes typically removes about 90% of external contamination.
  • If contamination is defined as radioactive material located in places it should not be, the goal of decontaminating people is removing all contamination, or as much contamination as possible without damaging the skin or creating other adverse effects.
  • Decontamination can be conducted without radiological monitoring if there is a lack of monitoring equipment.
  • In large mass contamination incidents, radiological screening can help identify those at risk who should be a priority for decontamination.
  • For high throughput, screeners may need to speed up initial radiation surveys of those at risk and target somewhat higher levels for the first stage of decontamination, during the early phase of an incident.
  • Subsequent decontamination cycles, perhaps at venues further away from the incident and first decontamination site, will continue the decontamination process for those who are not completely decontaminated in the initial cycles.
  • There is not a single "target value for decontamination" of people that would be appropriate for all types of incidents, under all circumstances. (See Selected References List below.)
  • Generally, decontamination efforts are usually stopped when the survey meter measures less than 2 or 3 times background, or if repeated decontamination cycles (usually 3) do not materially reduce the count rate. Consult guidance documents on this page for important details.
  • If appropriate external decontamination cycles fail to produce complete decontamination, the presence of internal contamination may be considered.
  • "Target values for decontamination" of people are NOT the same as target values for decontamination of things like buildings, vehicles, infrastructure, and ground during the long Recovery Phase of an incident.

Contamination is not the Same as Exposure

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What Factors May Affect the "Target Level Selected for Decontamination"?

  • Nature and location of the incident
  • Where and when the survey is conducted
  • Number of people who need to be surveyed vs. number of people available and qualified to do radiation surveys
  • Number of working, calibrated survey meters
  • Type of radiation detected by the survey meters available (alpha, beta, gamma) and settings (sensitivity) of the survey equipment
  • Type of contamination (alpha, beta, gamma) that needs to be surveyed and the radioisotope identified.
  • Pattern of contamination identified (e.g., loose, fixed, both; generalized/widespread vs. "spot" contamination)

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Nomenclature is Important in Understanding the Issues

  • Decontamination avoids potential health effects
    • Deterministic effects - dose threshold exists below which effect does not occur
      • Earliest effects - erythema, acute exudative radiodermatitis, the latter being most important
      • Intermediate/later effects - skin ulceration from a hot particle, skin ulcer with fibrosis
    • Stochastic effects - no threshold dose exists below which the effect will definitely not occur and the probability of occurrence is directly (but not necessarily linearly) proportional to the dose received
      • Long term effects - skin cancer, many other cancers
  • Screening vs. monitoring levels as targets for decontamination
    • What is a screening level?
      • A rapid assessment level, where action is warranted to prevent adverse effects and then quickly separate people that need more immediate decontamination
      • Often performed before decontamination and is meant for high throughput of personnel
    • What is monitoring level?
      • A more deliberate monitoring level, often post initial decontamination, or when the number of victims to be surveyed is small.
      • This monitoring is performed to look for lower levels of contamination, often taking much longer to perform.
    • See REMM information on: How to Perform a Survey
  • Disintegrations Per Minute (DPM) vs. Counts Per Minute (CPM)
    • DPM
      • How many atoms disintegrate per unit time, measured in units of Bq and Ci.
      • This does not take into account the energy of the disintegration.
    • CPM
      • What a radiation survey meter reads, i.e., how many (what percent) of the disintegrations have been detected by the meter.
      • Instrument-specific conversion factors (measuring counting efficiency) correlate CPM detected by the meter to DPM, and/or to other values used for radiation protection e.g., exposure rate in air (roentgen), absorbed dose rate in people (gray, sievert).
  • Definition of "spot" contamination
    • A skin area of 0.2 cm2 or a circle of 0.5 cm2 (FEMA and NCRP definitions)
    • Key guidance may differ in recommending target levels for spot decontamination for alpha, beta, and gamma.
    • See FEMA guidance documents on this page.
  • Loose vs. fixed sites of contamination
    • Loose contamination
      • Easily dislodged; removable by brushing off, washing or changing clothes.
    • Fixed contamination
      • "Stuck" onto the skin surface (or hair) so that neither brushing nor washing dislodges the radioactivity.
      • Normal skin growth and skin sloughing typically removes fixed skin contamination in about 2 weeks.

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Key Guidance Documents Recommend Different "Target Levels for Decontamination" of People

  • Various US and international agencies have recommended "target levels for radiation decontamination" of people during incidents of various kinds, sizes, and venues.
  • See table below showing decontamination targets published by various professional groups and government agencies
    Documentationβ/γ Screening CriteriaContamination RadionuclideSkin-to-Detector SeparationContamination ExtentExposure Time
    FEMA-REP-221,000 cpm fixed/ 10,000 cpm loose above bkgCs-137/Ba-137m2.54 cm0.2 cm2 spot with widespread14 days fixed/36 hours loose
    CRCPD Handbook10,000 cpm above bkgCs-137/Ba-137m2.54 cmWidespreadNot specified
    EPA 2017 PAG Manual2x bkgNot specifiedNot specifiedNot specified12 hours
    IAEA Operational Interventional Levels (OILs) for Reactor Emergenciesβ: 1,000 cps
    γ: 1 Sv/h    		Light Water Reactor emergency mixβ 2 cm
    γ: 10 cm    		Not specifiedNot specified
    NCRP Report No. 16110,000 Bq/cm2
    (1,000 Bq/cm2)    		Sr-901 cm0.2 cm2 spot with widespreadNot specified
    NCRP Report No. 165600,000 dpm/cm2Sr-901 cmNot specifiedNot specified
    (>6-12 hours)
    NCRP Report No. 1661,000 cpmSr-901 cmNot specified24 hours

    Source of table above: Caleigh Samuels, "Review of Current External Radiation Contamination Criteria" from presentation March 2019 to NCRP PAC 3 Committee. Presentation entitled: "Monte Carlo simulations evaluating suggested external contamination screening criteria for radiological and nuclear emergencies".

  • New! Recommendations differ about decision levels for decontamination, producing confusion about what to do.
  • REMM attempts to highlight the issues and provide context for understanding the problem.
  • Readers are encouraged to consult the original documents in the Selected References List below to learn about the issues in detail.
  • Professional responders using radiation survey meters should understand the significance of "meter readings" and "target values" for decontamination as they relate to
    • Type of radiation being detected (alpha, beta, gamma)
    • Specific kinds of meters and
    • Whether the focus of the survey of an individual is "spot" or "widespread" contamination
    • Whether the survey is addressing is "fixed" or "loose-plus fixed" contamination
    • How the survey instrument responds when it is stationary over a "hot spot" vs. following a continuous path over whole body survey
    • Particulars of the incident
      • Size of the incident and number of patients who need attention vs. the size of the decon team available with working equipment
      • Whether the site doing decon is performing "initial surveillance" triage decon for a large number of people or later-stage monitoring decon for people who have had previous decon elsewhere
  • Recommendations in the Selected Reference List of guidance documents below will help parse the issues noted above.
  • In a large incident, senior leaders, consulting with radiation protection specialists, will recommend clear and specific "targets for decontamination levels" for specific venues and circumstances, and these may change over time if circumstances change during the incident.
  • Understand that in some very large incidents, especially in cold weather, incident managers may recommend that large numbers of potentially contaminated patients get indoors, change clothes and/or shower first either at home or designated areas before undergoing formal surveys with a radiation detection meter and additional decontamination, if necessary.
  • Understand that recommendations for "target levels for decontamination" of people are NOT the same as those for vehicles, equipment, possessions, buildings, ground during the early or Recovery Phase of an incident.
  • According to ROSS guidance, there are 3 main detection activities or levels that are important to population monitoring. There is no consistent terminology to describe these levels, but these are the terms used for ROSS activities.
    • Contamination Detection Method: the method of initial detection of possible contamination and includes parameters such as type of detector used, speed of probe movement (or pedestrian speed through a portal), probe height, and areas surveyed
    • Initial Screening Decision Level: level of contamination (determined by a stationary measurement over an area of interest) that is high enough to warrant early intervention actions such as changing clothes or decontamination
    • Detailed Screening Decision Level: lower level of contamination (determined by a longer, stationary measurement over an area of interest) that some action to ensure that “fixed contamination does not remain on the person” should be considered after decontamination

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Selected List of Key Guidance Documents about
"Target Levels for Decontamination" of People

HHS/CDC

FEMA

NCRP

EPA

CRCPD

IAEA

Other Guidance