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Phases in the evaluation of the occupational exposure to a chemical substance/API. PHASE 1: Risk detection and initial assesment.

The aim of the hazard assessment is to determine the classification and labelling of the substance and to establish the concentration in the air of that substance at which it is considered that approximately almost all workers can be repeatedly exposed (day after day, in a job done throughout their life) without adverse effects; the aforementioned levels are known as the “Occupational exposure Limit” (OEL).

In the exposure control phase occupational exposure limits are required to determine whether or not the containment and protection measures are adequate.

Whenever there is no OEL an approximation can be used. An equation is given below to calculate the aforementioned value that is determined by the following parameters:

OEL (mcg/m3) = (NOAEL or LOAEL (mg/kg/day)× Body weight (kg))/(F1 ×F2 ×F3 ×F4 ×F5 (adjustment factors)×Respiratory Rate)

  • The OEL is expressed in mcg/m3 (ml/m³ or ppm for gases and vapours).
  • NOAEL: No Observed Adverse Effect Level
  • LOAEL (Lowest observed adverse effect level): Lowest dose capable of causing adverse effects.
  • Respiratory Rate= 10 m3 per 8 hours of work a day.

The first step in calculating the OEL is based on collecting dosage descriptor information taking the point of departure (POD) into account: NOAEL, LOAEL, LD50, LC50, BMD, etc., based on experimental studies (animals, humans) or epidemiological ones which occasionally have not been published. The exposure routes of the worker will be taken into account throughout the entire toxicological report. The point of departure must be objectively selected by an experienced toxicologist accredited by some Authority, for instance, EUROTOX.

occupational exposure to chemical substance

After the OEL value has been calculated and the toxicological analysis of the substance completed, the categorisation of the substance will be in accordance with the Naumann and Safebridge classifications taking into account the toxicological and pharmacological characteristics, as well as the physico-chemical properties of the same. The Naumann categorisation is based on five (5) categories, while the Safebridge only has four. Azierta categorisation is based on five (5) categories divides category 3 into two categories (3A and 3B) with a view to distinguishing the powerful active ingredients from those that are not powerful.

This categorisation will be the basis to establish: the H phrases (Hazard statements) and P ones (Precautionary statements) as well as the potential explosive, flammable or combustible effects.

We at Azierta have an expert toxicology team (AETOX, EUROTOX and ERT accredited) in determining occupational exposure limits and in APIs Categorization, which associates the exposure limits with specific safety measures (engineering control, standardised work processes and safety equipment). Our multi-discipline Occupational Health and Safety team has the expertise, moreover, to design complete health vigilance protocols to ensure safe work environments.


If you wish to learn more about this aspect of our work, visit Azierta: OEL and API Categorisation and follow us on our social networks



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