L135: Storage of Dangerous Substances (DSEAR)

What is L135?

L135 is the HSE's Approved Code of Practice (ACOP) and guidance for the storage of dangerous substances under the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR). It provides detailed guidance on how to store flammable liquids, gases, and other dangerous substances safely to prevent fires and explosions.

Dangerous substances release energy when they react - through burning, explosion, or violent chemical reaction. L135 focuses on substances that can form explosive atmospheres when mixed with air, and how to store them safely to minimise the risk of ignition and the consequences of any incident.

The guidance covers storage of flammable liquids like petrol, solvents, and oils; flammable gases including LPG and acetylene; and other substances that can create fire or explosion risks.

Who Needs This Document?

L135 is essential for:

• Motor vehicle repair workshops storing petrol, diesel, and solvents
• Paint spraying operations with flammable coatings and thinners
• Manufacturing facilities using or storing flammable materials
• Laboratories with flammable chemicals
• Construction sites storing fuels and solvents
• Farms and agricultural businesses with fuel stores
• Warehouses and distribution handling flammable goods
• Retail premises storing flammable products
• Printing and coating industries using solvent-based inks
• Any workplace storing flammable liquids or gases

Key Topics Covered

What are Dangerous Substances?

L135 covers substances that are:

Flammable or combustible:

• Flammable liquids (petrol, solvents, alcohols, oils)
• Flammable gases (LPG, natural gas, hydrogen, acetylene)
• Flammable solids and dusts
• Aerosols with flammable propellants

Capable of creating explosive atmospheres:

• Any gas, vapour, mist, or dust that can mix with air
• Creating a mixture that can be ignited by a spark or flame
• Resulting in explosion or flash fire

Common dangerous substances include:

• Petrol and diesel fuel
• Paints, varnishes, and thinners
• Cleaning solvents and degreasers
• Adhesives and sealants
• LPG (propane and butane)
• Acetylene and other fuel gases
• Industrial alcohols
• Printing inks and coatings

Risk Assessment for Storage

L135 requires a thorough risk assessment:

Identify dangerous substances:

• Review all substances stored or used
• Check safety data sheets (SDS)
• Consider by-products and waste
• Identify all storage locations

Assess the risks:

• How could an explosive atmosphere form?
• What ignition sources are present?
• Who could be harmed?
• What quantities are involved?
• How effective are current controls?

Consider:

• Physical and chemical properties
• Circumstances of use and storage
• Activities that could cause release
• Foreseeable incidents and emergencies

Storage Location and Construction

The ACOP provides guidance on storage facilities:

Location considerations:

• Away from other buildings where practicable
• Separated from ignition sources
• Accessible for emergency services
• Away from drains and watercourses
• Adequate ventilation provision

Construction requirements:

• Fire-resistant construction for larger stores
• Impervious bunding to contain spills
• Self-closing fire doors where appropriate
• Explosion relief for enclosed stores
• Adequate natural or mechanical ventilation

Storage types:

• Open-air storage compounds
• Fire-resistant storage buildings
• Storage cabinets within buildings
• Underground or above-ground tanks
• Cylinder storage cages

Quantity Limits and Segregation

L135 addresses storage quantities:

General principles:

• Store minimum quantities practicable
• Larger quantities require greater controls
• Some locations have regulatory quantity limits

Segregation requirements:

• Separate incompatible substances
• Keep oxidisers away from flammables
• Separate gases from liquids where appropriate
• Consider reactions if substances mix

Typical quantity thresholds:

• Small quantities may be stored in work areas in suitable cabinets
• Medium quantities require dedicated storage areas
• Large quantities need purpose-built facilities
• Threshold quantities vary by substance hazard classification

Ventilation Requirements

Adequate ventilation is critical:

Purpose of ventilation:

• Prevent build-up of flammable vapours
• Disperse any releases safely
• Maintain concentration below lower explosive limit (LEL)

Ventilation types:

• Natural ventilation through permanent openings
• Mechanical extraction ventilation
• Combination systems

Design considerations:

• Low-level and high-level openings for natural ventilation
• Openings sized appropriately for store size
• Mechanical systems suitable for flammable atmospheres
• Emergency ventilation where appropriate

Ignition Source Control

Eliminating ignition sources is essential:

Common ignition sources:

• Naked flames and hot work
• Electrical equipment and sparks
• Hot surfaces
• Static electricity
• Smoking
• Vehicles and machinery
• Lightning

Control measures:

• No smoking and naked flame policies
• Suitable electrical equipment in hazardous areas
• Hot work permit systems
• Static dissipation and earthing
• Vehicle exclusion zones
• Lightning protection where needed

Spill Containment

L135 covers spill prevention and containment:

Bunding requirements:

• Secondary containment for liquid stores
• Capacity to hold at least 110% of largest container
• Or 25% of total storage capacity (whichever greater)
• Impervious to stored substances

Spill response:

• Spill kits available and accessible
• Trained personnel
• Preventing releases to drains and watercourses
• Safe disposal of contaminated materials

Signs and Markings

Appropriate warning signs are required:

• Hazard warning signs at entrances
• No smoking signs
• No naked flames signs
• Emergency information
• Substance identification where appropriate
• Prohibition signs for restricted activities

Emergency Procedures

L135 addresses emergency planning:

Fire and explosion response:

• Alarm systems and detection
• Evacuation procedures
• Fire fighting equipment (where appropriate)
• Coordination with fire service
• Information for emergency responders

Spill response:

• Containment procedures
• Safe cleanup methods
• Personal protective equipment
• Disposal requirements

Legal Status

L135 is an Approved Code of Practice under the Health and Safety at Work etc Act 1974. Following its guidance provides the clearest route to compliance with DSEAR requirements for storage of dangerous substances. Courts give significant weight to ACOP guidance, and failure to follow it can be cited as evidence of non-compliance.

Why It Matters

Dangerous substance storage incidents can be catastrophic:

The Risks

Fires:

• Rapid fire spread with flammable liquids
• Intense heat release
• Potential for multiple casualties
• Property destruction

Explosions:

• Vapour cloud explosions
• Confined explosions in buildings
• BLEVE (boiling liquid expanding vapour explosion) with pressure vessels
• Structural damage over wide areas

Environmental damage:

• Contamination of soil and groundwater
• Pollution of watercourses
• Long-term cleanup costs
• Environmental prosecution

Historical Incidents

Major incidents have shaped the regulations:

• Buncefield fuel depot explosion (2005)
• Workplace fires from solvent storage failures
• Vehicle workshop explosions from petrol vapour
• Industrial accidents from improper chemical storage

Consequences of Non-Compliance

For workers and the public:

• Death from fire or explosion
• Severe burns
• Blast injuries
• Long-term health effects

For employers:

• Criminal prosecution and imprisonment
• Unlimited fines
• Civil compensation claims
• Business destruction
• Insurance invalidation
• Environmental liability

Benefits of Compliance

Proper storage provides:

• Prevention of incidents - removing conditions for fires and explosions
• Worker protection - safeguarding employees and others
• Property protection - preventing damage and loss
• Legal compliance - meeting regulatory duties
• Insurance cover - maintaining valid insurance
• Environmental protection - preventing pollution

Storage Quantity Guide

Note: Specific requirements depend on substance properties, location, and circumstances.

Key Compliance Steps

1. Identify all dangerous substances - complete inventory with quantities
2. Conduct DSEAR risk assessment - document hazards and control measures
3. Review storage arrangements - location, construction, ventilation
4. Implement control measures - bunding, ignition control, segregation
5. Establish emergency procedures - fire, spill, evacuation plans
6. Provide training - safe handling and emergency response
7. Install appropriate signs - hazard warnings and prohibitions
8. Maintain and review - regular inspections and assessment updates

Further Resources

• Dangerous Substances and Explosive Atmospheres Regulations 2002↗
• HSE DSEAR web pages↗
• HSG51 - Storage of flammable liquids in containers↗
• HSG140 - Safe use and handling of flammable liquids↗

This page summarises the ACOP L135. For full legal compliance, obtain and read the complete document from HSE. This summary is not a substitute for professional advice or the full ACOP text.