What is being assessed?
Acrylonitrile is used as a monomer to produce fibres, resins, plastics and rubbers. Its hazards must not automatically be attributed to the finished polymer: assessment identifies free monomer and exposure conditions. Production, transfer, sampling, maintenance and waste are reviewed because open operations can break the containment of a normally closed process.
A classification that changed
IARC evaluated acrylonitrile in 2024 as carcinogenic to humans, Group 1, with sufficient evidence for lung cancer. Some older information sheets retain previous classifications, which is why the date and organisation matter. The classification identifies the carcinogenic hazard; it does not calculate an individual person’s risk from a concentration or a single exposure.
Effects and routes of entry
NIOSH and ILO/WHO describe skin absorption, inhalation and irritation, as well as potentially serious systemic effects. Toxicity can appear after a delay following significant exposure. Vapour leaks, splashes and contaminated clothing all need investigation. A favourable air result does not demonstrate that the dose from skin contact is negligible.
Reduce releases and contact
Substitution where feasible, containment and closed transfers take priority, with specific review of connections. Protection against dermal exposure requires materials selected for the product and contact time. Procedures must cover equipment removal, cleaning and waste to avoid transferring contamination to other people or areas.
Flammability and stability
Acrylonitrile can polymerise under certain conditions involving heat, light or contact with incompatible substances. Supplier instructions on stabilisation and storage must be followed. Fire prevention goes beyond removing flames: it considers equipment, transfers and possible reactions. A leak is managed using the emergency plan and trained personnel, without relying on smell to decide whether access is safe.
Review example
In a hypothetical example, a plant reviews its assessment after updating carcinogenicity information. It pays particular attention to sampling and maintenance openings, where exposure may occur despite closed production. Measures and effectiveness checks are documented. A classification update does not establish that harm has occurred, but it does require checking that preventive decisions use appropriate information.
