When and why is it measured?
Risk assessment for exposure to chemical agents begins with an initial estimate (inventory of products and safety data sheets, quantities, methods of use, existing measures) that can be resolved using qualitative or simplified methods when the risk is clearly low or clearly unacceptable. However, measurements are required when exposure is significant and exceeding limit values cannot be ruled out, when regulations expressly require it (carcinogens, asbestos , lead, silica), or when it is necessary to verify the effectiveness of the measures adopted. Royal Decree 374/2001 establishes that measurement must be carried out when the assessment does not allow for any other conclusion, using standardized procedures and with a frequency that guarantees exposure control.
The measurements serve various purposes: to characterize the exposure of a group of workers with respect to a limit value (conformity assessment), to identify sources and times of greatest exposure to guide measures (diagnosis), to check the functioning of ventilation and enclosure systems (verification), or to detect changes over time (periodic monitoring). The objective determines the type of sampling (personal or environmental, full-day or task-based, integrated or direct reading), the number of samples, and the statistical analysis.
The UNE-EN 689 standard describes the reference strategy for assessing inhalation exposure against limit values: definition of similar exposure groups, basic characterization, representative sampling with a minimum number of measurements, statistical decision criteria, and a program of periodic measurements. INSST standards 553, 554, and 555 further develop these strategies, and standard 407 outlines the fundamentals of assessing exposure to chemical contaminants.
Sampling and measurement techniques
- Personal sampling. The sampling equipment is placed in the worker’s breathing zone (pump and support on the lapel) during the workday or task, and is the reference method for evaluating exposure against environmental limit values.
- Environmental or static sampling. Collection at fixed points to characterize sources, verify ventilation or monitor areas; it does not replace personal sampling to assess individual exposure.
- Supports and methods. Filters for particles, fibers and metals, activated carbon tubes or other adsorbents for organic vapors, impingers and silica tubes for certain gases, passive diffusion samplers and analysis by gravimetry, chromatography, spectrometry or microscopy according to the standardized method of the INSST or international organizations.
- Direct reading equipment. Gas detectors, photoionizers, particle monitors and colorimetric tubes that provide immediate results, useful for diagnosis, emergencies, confined spaces and peak control, with limitations in selectivity and accuracy.
- Physical agents. Integrating sound level meters and personal dosimeters according to UNE-EN ISO 9612 for noise ; accelerometers and analyzers according to UNE-EN ISO 5349 and 2631 for vibrations; lux meters and luminance meters; globe, wet and dry thermometers for thermal stress; dosimeters and detectors for radiation.
- Biological agents. Sampling of bioaerosols by impaction, filtration or impinger and analysis by culture or molecular techniques, with specific interpretation criteria in the absence of limit values.
- Quality and traceability. Calibration of pumps and equipment before and after sampling, blanks and controls, chain of custody, accredited laboratories or those participating in intercomparison programs, and uncertainty estimation.
- Documentation. Record of measurement conditions (tasks, times, ventilation, PPE, production, incidents), essential to interpret the results and repeat the strategy.
Interpretation and decisions
- Comparison with limit values. Calculation of daily and short-term exposure and comparison with the VLA-ED and VLA-EC of the INSST LEP document or with the binding limit values, applying the decision criteria of UNE-EN 689.
- Variability. Exposure varies between days and people; an isolated result below the limit does not guarantee compliance, hence the requirement for several measurements and statistical treatment.
- Combined exposure and other routes. Consideration of mixtures with additive effects, the dermal route and absorption by ingestion, complementing environmental measurement with biological control.
- Periodicity. Definition of a program of periodic measurements based on the relationship between exposure and the limit value, with review in case of changes in process, products or measures.
- Communication. Information of the results to the exposed workers and their representatives, and transfer to the health surveillance service.
- Action. The results feed into preventive planning: replacement, containment, extraction, organization, PPE and subsequent verification of effectiveness.
Organizational application: how to plan and manage hygiene measurements
- Start with the basic characterization of the exposure: agents, tasks, similar exposure groups, existing measures and regulations applicable to each agent.
- Decide for each agent and group whether qualitative evaluation, measurement or both are appropriate, and set the objective of each measurement (conformity, diagnosis, verification, control).
- Design the sampling strategy in accordance with UNE-EN 689 or the specific standard of the agent: type of sampling, number of samples, duration, representative conditions and analytical method.
- Hire or have access to competent personnel and accredited laboratories, with calibrated equipment and documented procedures.
- Record the conditions of each measurement and analyze the results with the decision criteria, uncertainty, and variability.
- Transfer the results to the risk assessment, the planning of measures and health surveillance, and inform the workers.
- Establish the program of periodic measurements and review it in case of changes or results close to the limit.
Preventive management software allows planning measurement campaigns by center and agent, recording results and sampling conditions, comparing them with updated LEPs, generating compliance reports, and linking the results with preventive measures and health surveillance.
Limits and common mistakes
- Measuring without defining the objective or the similar exposure groups, with results that do not allow for decision-making.
- Perform a single measurement and conclude conformity ignoring daily and inter-person variability.
- Sampling under non-representative conditions (reduced production, exceptional ventilation, tasks with greater exposure omitted).
- Using uncalibrated equipment, unvalidated methods, or laboratories without quality assurance.
- Confusing direct equipment readings with daily exposure assessments against the VLA-ED.
- Failure to document the measurement conditions or to communicate the results to workers and health surveillance.
Sampling and analysis methods and assessment strategies are detailed in INSST publications and technical standards; this sheet is for informational purposes only.
Practical example
Situation: A furniture manufacturing company wants to assess exposure to hardwood dust, a carcinogenic agent with a binding limit value, in the machining and sanding sections.
- Strategy. The prevention service defines two groups of similar exposure (machining with integrated extraction and manual sanding), plans full-day personal sampling with calibrated filters and pumps on three representative days per group, and records tasks, production and operation of the extraction.
- Analysis. The samples are analyzed by gravimetry in an accredited laboratory; the sanding results are close to the limit value and with high variability, while machining is clearly below it.
- Decision. The decision criteria of UNE-EN 689 are applied: machining compliant with annual periodic control; inconclusive sanding, which motivates improvements in the localized extraction of the sanders, vacuum cleaning instead of compressed-air cleaning and a new measurement campaign after implementing the measures.
- Follow-up. The results are communicated to the staff and the medical service, those exposed to carcinogens are recorded, and the conditions of each measurement are documented for future campaigns.
Regulatory and reference framework
- Royal Decree 374/2001, of April 6. Chemical agents; exposure assessment, measurements with standardized methods and periodicity.
- Royal Decree 665/1997, of May 12. Carcinogenic agents; exposure assessment and binding limit values.
- Royal Decree 286/2006, of March 10. Noise ; assessment and measurement according to standardized methods.
- NTP 553: Chemical agents: sampling and assessment strategies (I) (INSST) . Fundamentals of the sampling strategy.
- NTP 554: Chemical agents: sampling and assessment strategies (II) (INSST) . Decision criteria and treatment of results.
- NTP 407: Chemical contaminants: assessment of occupational exposure (II) (INSST) . Fundamentals of exposure assessment.
- Occupational exposure limits for chemical agents in Spain (INSST) . Reference limit values for comparison of results.
The UNE-EN 689 standard establishes the strategy for evaluating inhalation exposure against limit values, UNE-EN ISO 9612 the determination of noise exposure and UNE-EN ISO 5349 and 2631 that of vibrations; the INSST publishes the methods for taking samples and analyzing chemical agents.
