This page explains the major hazard potential of carbon capture utilisation and storage (CCUS) and will help CCUS licensees, operators and owners understand their duties.
The Carbon Capture Utilisation and Storage and Offshore Hydrogen Production (Miscellaneous Amendments) Regulations 2026 (CCUS 2026) extend to existing offshore installation and pipeline safety regimes to cover CCUS operations, transport of CO2 by pipeline, and offshore hydrogen production.
Scope of the 2026 Regulations
The 2026 Regulations extend to existing offshore installation and pipeline safety regimes to cover CCUS operations, transport of CO2 by pipeline, and offshore hydrogen production.
This includes making CO2 pipelines involved in CCUS a dangerous fluid and including CCUS pipelines in the offshore safety regime.
It also recognises that dense phase and supercritical CO2 can present major accident hazards if released at or above critical pressure.
CCUS capture installations are regulated under the Health and Safety at Work Act and other health and safety legislation.
Dense phase and supercritical CO2
In CCUS operations CO2 will be handled close to, or above, its critical pressure (73.82 bar) and temperature (31.04°C).
In this state, CO2 displays liquid-like properties and is referred to as dense phase or supercritical.
Significant hazards can occur when dense phase or supercritical CO2 experiences a rapid or total loss of pressure. This can result in:
- rapid phase change, resulting in sudden cooling and expansion which can cause explosive decompression, thrown debris and damaged equipment
- formation of cold CO2 clouds, which can accumulate at low levels, reducing visibility, affecting safe operation and emergency response
- material cracking and becoming brittle, this can increase the risk of structural damage or component failure
- potential for asphyxiation, due to displacement of oxygen in the surrounding atmosphere
CO2 is not classed as a dangerous substance under the Control of Major Accident Hazards Regulations (COMAH). In June 2011 HSE published Assessment of the major hazard potential of Carbon Dioxide. This report concluded that CO2, based on the evidence available at that time, has major accident hazard potential if released at, or above, its critical pressure.
However, where the risks are properly controlled the likelihood of a major hazard incident is expected to be very low.
CCUS 2026 reinforces that offshore hydrogen production and CCUS licensees, operators and owners have a duty to recognise and manage these physical hazards within updated safety cases and risk assessments.
To maintain safe operations, those that have a duty must continue addressing knowledge gaps in:
- modelling releases and dispersion
- separation distances
- design and operation of plant and pipelines
These areas remain critical for demonstrating suitable and sufficient major accident prevention measures.
Modelling releases and dispersion
Accurate modelling of large scale CO2 releases is essential for safety case submissions and emergency planning.
Key challenges that offshore hydrogen production and CCUS licensees, operators and owners must continue to address include:
- behaviour of dense or supercritical CO2 during sudden loss of pressure
- ground-hugging dispersion patterns
- low-temperature effects on materials and surroundings
The CCUS industry continues to develop and validate dispersion models through large scale experimental work. This evidence base helps HSE assess whether major accident hazards are being adequately controlled under the 2026 safety case regime.
Separation distances
Offshore hydrogen production and CCUS licensees, operators and owners must consider separation distances within offshore safety cases.
When setting appropriate separation distances, consider the following:
- Dangerous Toxic Load (DTL) methodologies
- Specified Level of Toxicity (SLOT) thresholds
- Significant Likelihood of Death (SLOD) thresholds
These remain the appropriate tools for assessing CO2 exposure impacts, even though land use use planning rules do not apply offshore.
Design and operation of plant and pipelines
CCUS 2026 extends to offshore pipeline legislation to cover CO2 pipelines. This means offshore hydrogen production and CCUS licensees, operators and owners must demonstrate that installations and pipelines carrying dense phase CO2 meet equivalent safety expectations to hydrocarbon systems.
Design considerations must include:
- material behaviour at low temperatures
- fracture propagation risks in CO2 pipelines
- corrosion control
- hydrate formation potential
- containment design for high-pressure CO2
Although dedicated CO2 design standards continue to develop, existing pipeline and process engineering standards, such as natural gas, may not always be sufficient.
Offshore hydrogen production and CCUS licensees, operators and owners must demonstrate, through engineering justification, that all major accident hazards associated with high-pressure CO2 are adequately controlled.
Find out more about regulating CCUS and offshore hydrogen production.