Chemical exposure remains one of the most persistent health risks in UK workplaces. Substances that appear routine within daily operations can still cause harm through inhalation or skin contact, with ingestion also possible. Employers are expected to understand when formal assessment becomes necessary and how changing work conditions alter exposure risk. The focus is on recognising risk at the point it arises, not after harm has already occurred.
Where do Hazardous Substances Arise at Work?
Many workplaces contain substances capable of causing harm, even where activities appear low risk. They are not limited to laboratories or factories and are not confined to specialist industrial settings. Potentially harmful substances are routinely introduced through standard operational tasks.
Cleaning involves detergents and disinfectants that can irritate skin or airways. Degreasers present similar risks when used regularly. Meanwhile, maintaining certain equipment can mean bringing in risks such as fuels, oils, adhesives, and sealants. Production and fabrication tasks generate dusts and fumes, with vapours generated through cutting or heating. Biological agents may also be present during waste handling. Healthcare delivery can introduce similar exposure.
Once these substances create a realistic possibility of exposure during normal work, a formal assessment becomes necessary. The requirement is driven by how substances are used and released during work activities, not just how familiar they appear within the organisation.
How is Hazardous Exposure Defined in Law?
Under the Control of Substances Hazardous to Health Regulations 2002, exposure is defined by the likelihood that a substance could cause injury or ill health. The law focuses on potential harm instead of confirmed illness.
Materials classified under the Classification, Labelling and Packaging Regulation and substances with published Workplace Exposure Limits fall within scope. Dust, fume, and vapour-generating materials are also captured, even if the original product is not supplied in a hazardous form.
If work activities create an opportunity for foreseeable exposure, a suitable assessment is required regardless of whether symptoms have already appeared.
Which Work Changes Require COSHH Reassessment?
Assessments cannot remain static. Exposure risk changes as workplaces change, processes adapt and materials are substituted. Introduction of new substances and alterations to work methods, plus changes to ventilation or relocation of tasks can all alter how substances are released or controlled.
Any delay in reviewing assessments allows exposure to continue without adequate control. Health effects linked to hazardous substances commonly develop gradually, meaning early warning signs may be overlooked until corrective action becomes reactive.
Whenever changes affect how workers come into contact with hazardous substances or assessment has not kept pace with operational change, a COSHH assessment must be considered.
How do Non-Routine Tasks Create Hidden Exposure?
Non-routine tasks present a heightened exposure risk because they operate beyond established operating procedures and controls, and a COSHH assessment must cover the exposure patterns they introduce. Maintenance and equipment cleaning can involve opening systems or disturbing residues. Fault investigation, contractor activity and temporary process changes may also introduce unfamiliar substances.
These may affect shared spaces and expose workers that are not directly involved in the task. Exposure levels can be higher than during normal operations, even if the work is brief.
If non-routine or contractor-led work change how substances are released or handled, the assessment must cover the exposure created by the task.
How Does Exposure Occur Without Direct Handling?
Exposure does not require direct contact with a hazardous substance. Indirect exposure routes are a frequent cause of overlooked risk, particularly in shared or multi-use environments.
Airborne contaminants generated by nearby activities may be inhaled by workers not involved in the task, including people who still fall within COSHH control arrangements. Contaminated surfaces can transfer substances to skin. Clothing and tools may carry residues into other work areas too.
To ensure that all affected workers are considered, including those not handling the substance directly, the assessment must account for these secondary exposure routes.
Which Substances Require COSHH Assessment?
Certain substances consistently trigger assessment due to well-established health effects. These substances appear across construction and manufacturing, as well as healthcare and facilities management.
Examples include isocyanates used in coatings and respirable crystalline silica generated during cutting, plus metal fumes from hot work and disinfectants used in clinical settings. Each presents a recognised exposure risk when controls fail.
In settings where these substances are present, COSHH assessment is expected to be in place and kept under review.
When do Health Trends Indicate a Review is Needed?
Patterns in reported symptoms can indicate that exposure is not being controlled adequately. These indicators often appear before serious illness develops.
Skin irritation or breathing discomfort linked to specific tasks may signal emerging problems, including gaps in COSHH controls. Absence patterns may also provide insight where symptoms worsen after certain activities.
If these trends suggest that existing controls are no longer sufficient, the assessment should be reviewed.
How Are Safety Data Sheets Used During Assessment?
Safety data sheets provide information on hazards and exposure routes, plus recommended controls used within COSHH assessment. They support assessment but do not replace it.
Data on health effects and storage requirements helps identify inherent risks associated with a substance. Emergency measures provide additional context. However, conditions described may differ from how substances are used on site.
This information is applied to actual working practices, taking account of task duration and frequency, plus the control measures in place.
What Evidence Must a COSHH Assessment Demonstrate?
Inspectors expect evidence that exposure risks have been identified and assessed, with appropriate controls applied before harm occurs. Documentation should show which substances were considered and how exposure routes were identified, alongside the control measures in place.
Where exposure is complex or monitoring is required, specialist input strengthens defensibility by confirming whether controls remain adequate.
The assessment record demonstrates that hazardous substances have been addressed in a structured way under COSHH.
In workplaces where hazardous substances are present, the record should show how exposure is prevented or controlled, how those controls are checked, and how review takes place following work changes.
Contact us to review your current arrangements and confirm whether updates are required to manage hazardous substances effectively.