COSHH · Mandatory · Pre-Construction
COSHH Assessment — Fuels and Oils
This COSHH assessment covers diesel, petrol, hydraulic oils, lubricants, and cutting fluids used on construction sites. It addresses dermatitis from prolonged skin contact, fire and explosion risks, and environmental contamination from spills. Bunded storage, spill kits, and drip trays must be provided for all fuel and oil storage areas.
Last reviewed: 29 March 2026 — This guide reflects UK law as of this date. COSHH Regs 2002 remains current with no amendments enacted as of 29 March 2026. Next scheduled review: 29 March 2027.
| Diesel DEEE | Diesel engine exhaust emissions are classified as a Group 1 carcinogen by IARC. Workplace Exposure Limit (WEL) for elemental carbon is 0.01 mg/m3 (8-hour TWA) |
| Skin contact | Diesel fuel and used engine oil are dermal carcinogens. Repeated unprotected skin contact causes occupational dermatitis and increases cancer risk |
| Fire / explosion | Diesel, petrol and LPG storage and use on site falls under the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR) |
| Environmental | Fuel spills are a pollution offence under the Environmental Permitting (England and Wales) Regulations 2016. All fuel storage must be bunded to 110% capacity |
| Hydraulic fluids | High-pressure hydraulic oil injection injuries are a surgical emergency. Hydraulic lines must be inspected before each shift and guarded where practicable |
| Enforcing authority | HSE for workplace health; Environment Agency for pollution; local authority petroleum licensing officer for petrol storage |
1. Diesel Engine Exhaust Emissions on Construction Sites
Diesel engine exhaust emissions (DEEE) were reclassified by the International Agency for Research on Cancer (IARC) as a Group 1 carcinogen — meaning there is sufficient evidence that they cause cancer in humans. The primary concern is lung cancer, but there is also evidence linking DEEE to bladder cancer. On construction sites, DEEE exposure arises from diesel-powered plant and equipment including generators, compressors, dumpers, excavators, telehandlers and concrete pumps.
The workplace exposure limit for DEEE is measured as elemental carbon and is set at 0.01 mg/m3 as an 8-hour time-weighted average. This is an extremely low limit, reflecting the carcinogenic potency of the substance. The limit applies to all enclosed or semi-enclosed spaces where diesel plant operates, including basements, tunnels, partially completed buildings and enclosed work areas. In practice, meeting this WEL requires either the elimination of diesel plant from enclosed spaces or the provision of forced mechanical ventilation combined with exhaust extraction at source.
Outdoor exposure is lower but not negligible. Where multiple items of diesel plant operate in close proximity, or where work is carried out downwind of running plant, cumulative exposure can be significant. The COSHH assessment must identify all diesel-powered equipment on site, assess where and how workers are exposed, and specify controls to reduce exposure as far as is reasonably practicable.
Electric plant alternatives should be assessed before defaulting to diesel
The hierarchy of control requires elimination to be considered first. Battery-electric and mains-electric plant is now available across a wide range of categories including mini-excavators, compressors, generators and telehandlers. Where electric alternatives exist and are practicable for the task, using diesel plant instead requires justification in the COSHH assessment. The HSE expects to see evidence that elimination was considered, and that where diesel plant is used, it is because no practicable electric alternative was available for the specific task and site conditions.
Where diesel plant must be used indoors or in enclosed spaces, local exhaust ventilation (LEV) must be fitted to capture emissions at source. This means direct-connected exhaust extraction ducted to outside the building. Simply opening windows or doors does not constitute adequate ventilation for DEEE control. Portable fans providing dilution ventilation are a supplementary measure, not a primary control.
Newer diesel engines fitted with diesel particulate filters (DPFs) and selective catalytic reduction (SCR) systems significantly reduce particulate and NOx emissions. However, DPFs require regular regeneration and maintenance to remain effective, and SCR systems require AdBlue replenishment. The COSHH assessment should specify the emission standard of diesel plant used on site (Stage IIIB, IV or V) and the maintenance regime for emission control systems.
2. Fuel Storage and DSEAR
The storage and handling of fuels and oils on construction sites falls under the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR). DSEAR requires employers to assess the risk of fire and explosion from dangerous substances, eliminate or reduce those risks, and classify areas where explosive atmospheres may occur into hazardous zones. Fuels commonly stored on construction sites include diesel, petrol, LPG, heating oil, and hydraulic fluids — all of which are dangerous substances under DSEAR.
The principal contractor must ensure that fuel storage arrangements comply with both DSEAR and environmental protection requirements. The following table sets out the key control measures for fuel storage on construction sites.
| Control measure | Requirement |
|---|---|
| Bunding | All fixed fuel storage tanks must be bunded to contain 110% of the tank capacity. Where multiple tanks share a bund, the bund must hold 110% of the largest tank or 25% of the total capacity, whichever is greater. Mobile bowsers must be double-skinned or placed within a drip tray during stationary use. |
| Labelling | All fuel containers, tanks, and bowsers must be clearly labelled with the substance name, hazard pictograms (GHS/CLP), and reference to the safety data sheet. Pipework carrying fuel must be colour-coded and labelled at regular intervals and at each valve or junction. |
| Access control | Fuel storage areas must be secured against unauthorised access. Lockable valves, padlocked enclosures, and restricted key issue are the minimum standard. Fuel storage areas must be separated from site offices, welfare facilities, and areas where ignition sources are present. |
| Spill kit | An appropriately sized spill kit must be located adjacent to every fuel storage point and at every refuelling location. Spill kits must contain absorbent materials suitable for the fuel type, disposal bags, and PPE. All operatives who handle fuel must be trained in spill response procedures. |
| Petroleum licence | The storage of petrol above the prescribed quantity (currently 275 litres from a petroleum storage certificate exemption) requires a petroleum storage certificate from the local authority petroleum licensing officer. This applies to petrol only, not diesel. Sites storing petrol must comply with HSG176 and the conditions of the certificate. |
Refuelling operations present specific risks. Diesel has a flashpoint of approximately 52°C, which is below its auto-ignition temperature but well above ambient temperature in the UK, so the vapour risk from diesel is relatively low in normal conditions. Petrol, by contrast, has a flashpoint of approximately -43°C and produces flammable vapour at all ambient temperatures encountered on UK sites. Refuelling with petrol requires earthing/bonding of the delivery vessel to the receiving tank to prevent static discharge, and must be carried out in the open air away from ignition sources.
Hydraulic fluids are classified under COSHH because of the health hazards they present on skin contact and, critically, the risk of high-pressure injection injury. Hydraulic systems on plant operate at pressures of 200 to 400 bar. A pinhole leak in a hydraulic line can inject oil through skin and into subcutaneous tissue at these pressures, causing a medical emergency that requires immediate surgical intervention. The COSHH assessment must address hydraulic oil as a substance hazardous to health and specify inspection, guarding, and emergency response controls.
DSEAR zone classification is required where flammable vapours may accumulate
Where petrol or LPG is stored or dispensed, the area around the storage point must be classified into hazardous zones under DSEAR. Zone 1 applies where an explosive atmosphere is likely to occur in normal operation; Zone 2 where it is not likely in normal operation but may occur for short periods. Electrical equipment within these zones must be ATEX-rated for the zone classification. Diesel storage does not normally require zone classification because diesel vapour does not form an explosive atmosphere at normal ambient temperatures.
3. Common Mistakes
Running diesel generators indoors without exhaust ventilation
Diesel generators operated inside partially completed buildings, basements or enclosed compounds without direct exhaust extraction expose workers to DEEE concentrations that will exceed the WEL rapidly. Natural ventilation through open doors and windows is not sufficient to control DEEE exposure indoors. Exhaust gases must be ducted directly to outside the building, and supplementary forced ventilation provided to dilute residual emissions. Where this is not practicable, electric generators or mains power must be used instead.
No spill kit at refuelling points
Every location where fuel is stored or dispensed must have an appropriately sized spill kit immediately to hand. This includes mobile bowsers and temporary refuelling locations, not just fixed tanks. The spill kit must contain absorbent materials matched to the fuel type (hydrophobic absorbents for fuel on water, general-purpose absorbents for hard surfaces), disposal bags, nitrile gloves, and eye protection. Workers who handle fuel must know where the spill kit is and how to use it.
Workers using fuel without gloves or skin protection
Diesel fuel and used engine oil are dermal carcinogens. Repeated skin contact without adequate protection causes occupational dermatitis and increases the long-term risk of skin cancer. Workers who refuel plant, change engine oil, maintain hydraulic systems, or clean fuel-contaminated components must wear nitrile or neoprene chemical-resistant gloves as a minimum. Barrier cream is not an adequate substitute for gloves. Where clothing becomes fuel-soaked, it must be changed immediately — fuel-soaked clothing held against the skin greatly increases dermal absorption.
Not assessing hydraulic oil under pressure as a COSHH hazard
Hydraulic oil under high pressure presents a hazard that goes beyond conventional chemical exposure. A high-pressure injection injury from a pinhole leak in a hydraulic line is a surgical emergency — the oil is injected beneath the skin at pressures up to 400 bar, causing tissue necrosis and potentially requiring amputation if not treated within hours. The COSHH assessment must address hydraulic oil both as a skin-contact hazard and as an injection-injury risk, specifying pre-use inspection of all hydraulic lines, guarding of vulnerable connections, and an emergency response procedure that includes immediate hospital transfer.
Refuelling near ignition sources without earth bonding
Refuelling operations with petrol or from bulk diesel bowsers in the vicinity of ignition sources present a fire and explosion risk. Petrol vapour is heavier than air and can travel considerable distances to reach an ignition source. Earth bonding between the delivery vessel and the receiving tank prevents static discharge during fuel transfer, which is a common ignition mechanism. Refuelling must be carried out in the open air, away from hot works, running plant, and electrical equipment. No smoking controls must be enforced within the refuelling exclusion zone.
5. Frequently Asked Questions
How does DSEAR apply differently to diesel compared with petrol?▾
Diesel has a flashpoint of approximately 52°C and does not produce flammable vapour at normal UK ambient temperatures. Petrol has a flashpoint of approximately -43°C and produces flammable vapour at all ambient temperatures. Under DSEAR, petrol storage and dispensing areas require hazardous zone classification (typically Zone 1 or Zone 2), ATEX-rated electrical equipment within those zones, earthing and bonding during fuel transfer, and in many cases a petroleum storage certificate from the local authority. Diesel storage does not normally require zone classification, but it does require bunding, spill containment, and controls against ignition sources during refuelling. Both fuels require a DSEAR risk assessment, but the controls for petrol are significantly more onerous.
When is carbon monoxide monitoring required for diesel plant on site?▾
Carbon monoxide (CO) monitoring is required whenever diesel-powered plant or generators operate in enclosed or semi-enclosed spaces — including basements, tunnels, partially completed buildings, and any area where natural ventilation is restricted. CO is produced by incomplete combustion and is an acute asphyxiant at high concentrations. Personal CO monitors should be worn by all workers in the affected area, and fixed CO alarms with audible and visual warnings should be installed at the point of use. CO monitoring is also advisable in outdoor situations where multiple items of diesel plant operate in a confined working area, such as a deep excavation or a courtyard surrounded by buildings.
What are the bunding requirements for fuel storage on construction sites?▾
All fixed fuel storage tanks with a capacity exceeding 200 litres must be bunded. The bund must contain 110% of the capacity of the single tank, or where multiple tanks share a bund, 110% of the largest tank or 25% of the total combined capacity, whichever is greater. The bund must be impervious to the fuel stored, with no drainage valve (or if a valve is fitted, it must be locked closed and opened only under supervision). Mobile bowsers must be double-skinned (integrally bunded) or placed within a portable drip tray during stationary use. These requirements derive from the Oil Storage Regulations and the Environmental Permitting Regulations, and are enforced by the Environment Agency.
Do hydraulic oils fall under COSHH?▾
Yes. Hydraulic oils are substances hazardous to health under COSHH because of the dermal health effects of prolonged or repeated skin contact (dermatitis, oil acne, and potential carcinogenicity of used oils containing combustion by-products). In addition, the COSHH assessment must address the unique hazard of high-pressure injection injury, where a pinhole leak in a hydraulic line injects oil through the skin at pressures up to 400 bar. This is a surgical emergency that can result in tissue necrosis and amputation. The COSHH assessment must specify gloves for routine handling, pre-use inspection of all hydraulic lines and fittings, guarding of vulnerable connections, and an emergency response procedure for injection injuries that includes immediate hospital transfer with a description of the injury mechanism.
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