What question do they answer?
A filter or tube may acquire material during transport, opening or handling. A blank helps investigate these contributions within occupational hygiene measurement. Its role is particularly important when the analysed mass is small and modest contamination could appreciably change the calculated concentration.
Different controls have different functions
A laboratory blank provides information about the medium and analytical operations; a field blank incorporates handling defined for the survey. They are not interchangeable. For passive samplers, the blank remains unexposed to the atmosphere being measured. Identification must state the blank type and its batch.
Plan before sampling
Number, media, containers and handling are agreed with the laboratory. A specific method may require several blanks: no universal number suits every survey. Preparing them after doubtful results arrive does not reproduce the original journey or operations and cannot recover that missing evidence.
Interpret without hiding anomalies
Blank correction, where applicable, follows the analytical method; it is not subtracting arbitrary values until a favourable result appears. High or widely scattered values require review of batch, cleanliness and handling. Original results and the technical decision on validity, correction or repeat sampling must be retained.
Investigation example
In a hypothetical example, several dust samples contain little mass and their blanks show similar increases. Before concluding that everyone had low exposure, possible medium changes or contamination during transport are reviewed. The problem may affect quantification capability even if laboratory weighing was correct.
Useful traceability
A field sheet should link each blank to samples, date and operations performed. Recording who opened media, where they were stored and how they reached the laboratory helps locate the cause. A blank complements chain of custody and analytical controls; it does not replace a representative exposure strategy.
