In the UK, businesses that discharge surface water potentially contaminated with hydrocarbons (such as from vehicle servicing areas, car parks or industrial yards) increasingly face stringent regulatory requirements to prevent pollution of drains, groundwater and watercourses. One key area of compliance is the use and ongoing management of oil separators – including the installation of alarms and detailed maintenance logging.
Regulatory Background
UK environmental law places a clear obligation on businesses to prevent pollution. Failure to do so can lead to prosecution, unlimited fines and even imprisonment. To support this legal duty, regulators such as the Environment Agency provide detailed guidance in documents like Pollution Prevention for Businesses, which sets out expectations for equipment such as oil separators.
Crucially, this guidance confirms that since 1 January 2021, it is a legal requirement for oil separators (as well as other products with BS EN 858 certification, such as the range of SPEL ESR Treatment Systems) supplied in England, Scotland and Wales to be fitted with an automatic warning device or high-level alarm. This requirement is not merely “best practice” but is made law through the Construction Products Regulations framework.
Why Alarms Are Now Mandatory
Historically, British Standards (notably BS EN 858-2:2003, the specification for separator systems for light liquids) recommended that oil separators be equipped with visual/audible warning devices to signal when oil accumulation reaches high levels. Regulators used this standard in guidance to define what an effective separator installation looked like.
However, from 2021, this recommendation has been elevated to a legal requirement for separators supplied into the UK market via the Construction Products Regulations (CPR). The CPR is a product-safety framework that ensures construction products (including pre-fabricated oil separators) meet designated performance and safety standards before they can be placed on the Great British market.
Under the CPR regime, compliance with designated standards like BS EN 858 is taken as evidence that the product meets essential requirements. Therefore, if an oil separator is supplied without an alarm fitted in accordance with these standards, it may be deemed non-compliant with the CPR, making it illegal to supply or place on the UK market.
See a full overview of our available Stormwater alarms here
Technical Expectations of Alarm Systems
From a technical standpoint, an alarm on an oil separator should:
- Reliably detect when the oil level approaches the storage capacity, triggering a high-level alert.
- Provide visual and/or audible indication, and where appropriate, remote signalling to a supervisory point.
- Be suited to the separator design and site use case, including explosion-protected or intrinsically safe installations if required by the environment.
Separators may also use supplementary sensors to indicate silt build-up, which can significantly impair separator performance. While silt alarms are not universally mandated, they are strongly recommended where silt ingress is likely.
Maintenance and Record-Keeping Requirements
Beyond the installation of alarms, UK guidance stresses the importance of regular inspection, maintenance and record-keeping:
Inspection Frequency:
BS EN 858-2 and related guidance recommend separator systems, including associated alarms, be inspected and maintained at least every six months by trained personnel to ensure functionality.
Integrity Testing:
A full integrity test of the separator unit should be conducted at least once every five years.
Maintenance Logs:
Detailed logs of installation, periodic inspections, alarm activations, servicing, cleaning and repairs must be maintained. These logs must
be readily available for inspection by regulators at any time. Clear documentation demonstrates compliance and supports effective environmental management.
This heightened focus on documentation means that the legal duty to prevent pollution extends beyond physical installation: it also covers how the system is managed over its operational life.
SPEL have prepared a full range of Operation and Maintenance Manuals that include a maintenance log for easy maintenance of devices. These can be easily downloaded from the Data Zone on our website.
Practical Implications for Engineers, contractors, businesses and end clients.
Responsible for drainage infrastructure design, installation and maintenance, this legal framework has several implications:
- Design Stage: Ensure any specified oil separator system includes a compliant alarm package as an integral element, not as a retrofit option.
- Product Selection: Choose separators and alarm systems that meet BS EN 858 requirements and can be demonstrated to conform under the Construction Products Regulations regime.
- Operational Management: Implement a robust inspection and maintenance regime, supported by detailed logging processes that capture all alarm events and service activities.
- Audits and Inspections: Be prepared for regulatory inspections where both the alarm system and the maintenance documentation could be scrutinised.
The UK’s requirement for alarms on oil separators reflects a broader shift in environmental regulation: prescriptive technical compliance backed by legal enforceability.
Since 2021, separators must not only be capable of capturing hydrocarbons but also of actively alerting site operators when the oil/hydrocarbon level reaches the predetermined level inline with BS EN 858. This requirement, embedded in the Construction Products Regulations and reinforced through operational guidance, elevates alarm systems from optional add-ons to essential components of pollution prevention strategy.
By ensuring compliant design, rigorous maintenance and comprehensive record-keeping, engineers and all organisations can both meet their legal obligations and significantly reduce the risk of environmental harm and regulatory action.
