What are they?

Occupational Exposure Limits (OELs) are reference values used to assess and control workers’ exposure to chemical agents present in the workplace, mainly through inhalation.

In Spain, the National Institute for Occupational Safety and Health (INSST) publishes annually the document Occupational Exposure Limits for Chemical Agents in Spain.

OELs mainly include:

1. Environmental Limit Values (VLA), referring to the concentration of the chemical agent in the air within the breathing zone.
2. Biological Limit Values (VLB), used as reference values for specific biological indicators of exposure.

The updated values for each substance can be consulted in the INSST Occupational Exposure Limits Database (BDLEP), by searching for the substance name or its CAS number.

Environmental Limit Values

The main VLA are:

1. VLA-ED (Daily Exposure): reference value for the time-weighted average exposure during an 8-hour working day.
2. VLA-EC (Short-Term Exposure): reference value for short-term exposures, normally over a 15-minute period, unless a different reference period is established for a particular agent.

VLA-ED and VLA-EC have different meanings and, when a substance has both values, they should be assessed together.

VLA are reference values for assessing and controlling exposure. They do not represent a boundary between a “safe” and a “dangerous” situation, nor do they by themselves guarantee the absence of adverse health effects.

Therefore, not exceeding a VLA does not mean that preventive measures are unnecessary. The assessment must take into account the characteristics of the agent, the actual working conditions, the duration and frequency of exposure, the routes of entry and the characteristics of the exposed workers.

Biological Limit Values

Biological Limit Values (VLB) are reference values for specific biological indicators associated with exposure to chemical agents.

Biological monitoring can provide information on a worker’s overall exposure, since, depending on the substance and the indicator used, it can integrate absorption through different routes, including inhalation, dermal absorption and ingestion.

It may be particularly useful:

1. as a complement to environmental measurements;
2. where dermal exposure makes a significant contribution;
3. to assess overall exposure to the agent;
4. to verify the effectiveness of preventive measures;
5. or where there are significant differences between environmental exposure and the amount actually absorbed.

VLB are not intended to diagnose an occupational disease or, by themselves, to determine whether adverse health effects are present or absent.

Occupational exposure limits do not, by themselves, guarantee protection for all workers

Limit values are established on the basis of the available scientific knowledge and certain critical health effects. Therefore, particularly susceptible workers may experience effects at concentrations below the reference value.

In addition, VLA mainly focus on exposure through inhalation and do not always adequately reflect other routes of entry, such as dermal absorption.

The assessment should therefore take into account, among other aspects:

1. inhalation;
2. dermal absorption;
3. accidental ingestion;
4. exposure to mixtures of chemical agents;
5. duration and frequency of exposure;
6. acute and chronic effects;
7. sensitisation;
8. carcinogenicity, mutagenicity or reproductive toxicity;
9. the possibility of endocrine effects;
10. and individual characteristics that may increase susceptibility.

OELs established for specific chemical agents should not automatically be used to assess mixtures of substances. Where workers are simultaneously exposed to several agents, a specific assessment must be carried out, taking into account their effects and possible interactions.

Carcinogenic, mutagenic and reprotoxic substances

Carcinogenic, mutagenic and reprotoxic agents require specific preventive measures.

Royal Decree 665/1997, in its current wording, includes reprotoxic agents within its scope and establishes specific requirements concerning risk assessment, substitution, exposure reduction, hygiene, health surveillance, information and training.

The existence of an occupational exposure limit for one of these substances must not be interpreted as a level of exposure without risk. The preventive priority is to avoid exposure by substituting the agent or process where technically possible and, where this is not possible, to reduce exposure to the lowest technically achievable level.

Attention should also be paid to substances for which no occupational exposure limit has yet been established. The absence of a VLA or VLB does not mean that exposure is safe or that it can be excluded from the risk assessment.

Pregnancy, breastfeeding and reproductive health

Occupational exposure limits should be used with particular caution during pregnancy and breastfeeding.

The INSST LEP 2026 document states that, in principle, OELs cannot be considered an adequate criterion for assessing the risk arising from exposure to chemical agents for a pregnant worker or a worker who is breastfeeding, because limit values are established taking into account a specific critical effect which may not correspond to possible effects on pregnancy or breastfeeding.

Risk assessment must also take into account possible effects on fertility and reproductive function among workers, both women and men.

Spanish Law 31/1995 requires risk factors that may affect reproductive function to be taken into account, including exposure to physical, chemical and biological agents with possible mutagenic or reproductive toxic effects.

In addition, the Regulation on Prevention Services establishes specific measures for pregnant workers and workers who are breastfeeding. Particular attention must be paid to certain substances classified for their effects on reproduction, carcinogenic and mutagenic substances, lead, mercury and its compounds, carbon monoxide and other agents capable of penetrating the skin.

Therefore, a VLA must not be used as the sole criterion for deciding that exposure is acceptable during pregnancy or breastfeeding. Where a specific risk exists, the measures established by occupational health and safety legislation must be applied, prioritising the elimination or avoidance of exposure.

What should be done?

The existence of an occupational exposure limit does not replace the assessment and prevention of chemical risks.

When hazardous chemical agents are present at work, the following steps should be taken:

1. Identify all substances and mixtures used or generated, including intermediate products and waste.
2. Consult the available information, particularly safety data sheets, labels, CLP classification and available toxicological information.
3. Check whether a current VLA or VLB exists for each agent in the updated INSST OEL document.
4. Assess all routes of exposure, not only inhalation.
5. Take simultaneous exposure to several agents and possible interactions into account.
6. Prioritise the elimination or substitution of hazardous agents wherever possible.
7. Where substitution is not possible, reduce exposure through technical and organisational measures, such as closed systems, local exhaust ventilation, process isolation, automation, appropriate maintenance, cleaning and safe working procedures.
8. Use personal protective equipment as a complementary measure, not as a substitute for collective and organisational preventive measures.
9. Carry out environmental measurements or biological monitoring when necessary to verify and quantify exposure.
10. Review the risk assessment periodically whenever substances, processes, working conditions or scientific knowledge change.

The preventive strategy should be particularly rigorous where carcinogenic, mutagenic or reprotoxic substances, sensitising agents or substances with other serious health effects are involved.

LEP 2026: relevant changes

The 2026 edition of the Occupational Exposure Limits for Chemical Agents in Spain includes several changes compared with previous editions. These include:

1. updated VLA for asbestos, benzene, vinyl cyanide, and certain agents present in underground mining and tunnel construction;
2. updated values for diisocyanates, ethylbenzene, formamide and lead;
3. an updated VLB for benzene;
4. inclusion of biological limit values for lead and ethylbenzene, with their entry into force scheduled for the coming years;
5. updated classifications for certain agents;
6. removal from the table of the value for 1,2,3-trichloropropane, as its value is under review;
7. inclusion of chemical agents currently being studied for the establishment or modification of VLA or VLB.

The latest edition of the OEL document and the INSST BDLEP should always be consulted, as values may be modified in response to new scientific evidence or regulatory changes.

Legislation and reference documentation

1. Law 31/1995, of 8 November, on Occupational Risk Prevention.
2. Royal Decree 374/2001, of 6 April, on the protection of the health and safety of workers against risks related to chemical agents at work.
3. Royal Decree 665/1997, of 12 May, on the protection of workers against risks related to exposure to carcinogenic, mutagenic or reprotoxic agents at work, in its current wording.
4. Royal Decree 39/1997, of 17 January, approving the Regulation on Prevention Services, particularly Annexes VII and VIII concerning pregnancy and breastfeeding.
5. Occupational Exposure Limits for Chemical Agents in Spain. INSST, 2026 edition.
6. Occupational Exposure Limits Database (BDLEP). INSST.
7. Technical Guide for the Assessment and Prevention of Risks Related to Chemical Agents Present in the Workplace. INSST, 2022.

Last updated: August 2026