Understand Target Levels for Decontamination of People
- 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
Screening vs. monitoring levels as targets for decontamination
- 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
Disintegrations Per Minute (DPM) vs. Counts Per Minute (CPM)
- 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
Definition of "spot" contamination
- 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.
- 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).
Loose vs. fixed sites of 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 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.
- Recommendations differ, producing confusion about what to do. (See Selected References List below.)
- 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.
- NCRP is expected to publish in 2014 a document on the Recovery Phase of an incident which addresses this issue.
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Selected List of Key Guidance Documents about "Target Levels for Decontamination" of People
- Approach to Optimizing Decision Making for Late-Phase Recovery from Nuclear or Radiological Terrorism Incidents, SC 5-1 (NCRP draft in progress), Bethesda, MD.
- Population Monitoring and Radionuclide Decorporation Following a Radiological or Nuclear Incident, (NCRP Report No. 166), Bethesda, MD, 2011.
- Responding to a Radiological or Nuclear Terrorism Incident: A Guide for Decision Makers (NCRP Report No. 165), Bethesda, MD, 2010.
- Management of Persons Contaminated with Radionuclides: Scientific and Technical Bases (NCRP Report No. 161, Vol. II), Bethesda, MD, 2010. Chapter 5: Performing Surveys and Controlling Personnel and Area Contamination.
- Management of Persons Contaminated With Radionuclides: Handbook (NCRP Report No. 161, Vol. I), Bethesda, MD, 2008.
- Key elements of preparing emergency responders for nuclear and radiological terrorism (NCRP Commentary No. 19), Bethesda, MD, December 2005. Purchase required; see Free overview (PDF - 219 KB)
- The 1992 EPA Protective Actions Guide Manual and its Supplement
- The PAG manual is undergoing revision. Until the final version is available, the following document is appropriate for interim use.
- Criteria for use in preparedness and response for a nuclear or radiological emergency, General Safety Guide, No. GSG-2, (PDF - 1.45 MB) (FAO, IAEA, ILO, PAHO, WHO, March 2011)
- Manual for First Responders to a Radiological Emergency (PDF - 2.2 MB) (CTIF, IAEA, PAHO, WHO, October 2006)
- Generic Procedures for Medical Response During a Nuclear or Radiological Emergency (PDF - 2,224 KB) (IAEA, WHO, July 2005)