A calibration check is simply a series of measurements on a film or coupon with a known amount of lead-based paint applied to it (i.e., a standard reference material [SRM]) to verify that the instrument is working properly. These measurements are averaged and then the value is compared to the calibration check limits of that particular XRF analyzer to determine if the instrument is within those limits. (Note: The inspector cannot recalibrate the XRF analyzers; recalibration must be done by the manufacturer. This procedure is only to verify that the instrument is in proper calibration in accordance with the PCS.) Do not use an XRF analyzer if the calibration check results are outside the PCS tolerance limits.
A check of the instrument’s calibration is the first step in ensuring proper operation of the instrument and in determining that the data generated during the inspection is accurate.
Each instrument’s PCS includes a protocol for conducting a calibration check. This check must be done, at a minimum,
· At the beginning of each lead-based paint inspection;
· At least every 4 hours during the inspection, or more frequently if the manufacturer recommends it; and
· At the end of each inspection.
The lead-based paint inspector will need the following items in order to conduct a calibration check.
· The X-ray fluorescence analyzer which will be used to conduct the inspection;
· The PCS for the XRF analyzer;
· A calibration check test results form;
· A Standard Reference Material (SRM) closest to 1.0 mg/cm² (usually the NIST 1.02 SRM film is used);
· A piece of solid wood (not plywood), Styrofoam, or other nonmetal rigid substrate unless the SRM will be attached directly to the XRF probe.
Before the beginning testing with the dwelling the inspector must:
· Attach the SRM to the piece of nonmetal substrate material (or attach it directly to the XRF probe),
· Take three XRF measurements (as directed by the instrument’s PCS) on the SRM;
· Record each of the readings on the calibration check test results form,
· Average the three readings on the calibration check test results from, and
· Compare the result with the calibration check limits on the PCS for the XRF analyzer.
In most cases, the average will fall within the calibration check limits listed on the PCS for that instrument. However, should the average of the three readings fall outside of the limited for the instrument, the manufacturer’s instructions should be followed to bring the instrument back into control. A second calibration check should then be conducted to determine if the instrument is within the tolerance limits before being used.
If the recommended actions do not result in the readings falling within the calibration tolerance limits, the XRF operator should contact the manufacturer for additional instructions. The instrument may require service at the manufacturer’s repair facility. Until a valid calibration check has been completed, that instrument must not be used for testing.
Once testing has begun, a second calibration check must be conducted at least every four hours or at the end of the lead-based paint testing, whichever occurs first. Some inspectors choose to check their instrument’s calibration more frequently to avoid losing several hours of data should the intermediate or final calibration check result in readings outside the tolerance limits for that instrument.
Readings not accompanied by successful calibration checks at the beginning and end of the testing period are unreliable and should be repeated after a successful calibration check has been made. If a backup XRF instrument is used as a replacement, it must successfully pass the initial calibration check test before retesting the affected test location.
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