Lead-Based Paint Inspection Methods and Equipment
Inspection versus assessment
An inspection determines whether and where LBP is present, which requires testing every component type, in every room, on each distinct substrate where testing is required by the protocol, with combinations of low and high lead. A risk assessment determines whether hazards exist. Candidates lose points by describing a risk assessment when asked what an inspection delivers.
XRF principles
Portable XRF analyzers (isotope-source or X-ray tube) measure lead in paint by fluorescence. Qualification is substrate-specific: readings on wood, drywall/plaster, concrete, brick, and metal behave differently, and a single calibration or mode does not transfer across substrates. Results are compared to the federal definition of LBP (1.0 mg/cm² or 0.5% by weight). Two modes exist: direct reading (outcome in mg/cm²) and, on some instruments, a paint-film mode.
Calibration, verification, and substrate correction
Perform a daily calibration check with the reference standard(s) the manufacturer specifies, and verify with readings on known standards; perform substrate correction where the instrument's substrate response is significant by taking readings on bare, lead-free substrate of the same type and subtracting. Record instrument serial number, mode, dwell time, and calibration results in the field data.
Error sources
False positives arise from substrate interference, paint containing other heavy elements, or reading through to underlying paint layers. False negatives arise from insufficient dwell time, improper substrate correction, reading the wrong side of a component, or testing a repainted surface assumed representative. Confirm inconclusive readings with paint chip sampling (laboratory analysis by AAS or ICP) for that component.
Worked rule of thumb
Matching substrates is the whole game: a reading high on wood does not qualify plaster in the same room. If an XRF reading is near the 1.0 mg/cm² threshold, treat it as inconclusive and confirm by laboratory paint chip - the cost of a chip is trivial compared to a misclassified component. Never report an average across components.