prEN 12101-12: SHEVS Design for Time-Dependent Fires (Draft)

prEN 12101-12 is the draft part of the EN 12101 family covering smoke and heat exhaust ventilation system (SHEVS) design for time-dependent fires. Where current SHEVS design typically uses steady-state assumptions (a fixed fire size, a fixed smoke production rate), Part 12 addresses how systems perform when the fire grows, peaks and decays over time.

Part of the BS EN 12101 standard family.

The “prEN” prefix indicates this is a provisional European Norm: the standard is still in CEN’s development process and has not yet been published. Products cannot currently carry a CE or UKCA mark “against EN 12101-12.”

Why time-dependent design matters

Real fires are not steady-state events. They:

• Grow through ignition, growth and peak phases (typically following t-squared fire growth curves)
• Peak at a maximum heat release rate (HRR) that depends on the fuel and ventilation conditions
• Decay as fuel is consumed

A SHEVS that performs adequately at steady-state peak may behave very differently during the growth phase, when smoke layers form and smoke production rates change rapidly. Time-dependent analysis is increasingly important for:

• Large atria and shopping centres where evacuation may take longer than fire growth
• Mixed-use buildings with varied fire loads
• Buildings where fire engineering is being used to deviate from prescriptive guidance
• Performance-based fire safety design under BS 7974 and similar frameworks

What the draft addresses

The draft standard is expected to provide:

• Methodologies for time-dependent SHEVS design
• Inputs and assumptions for fire growth curves
• Calculation approaches for transient smoke layer behaviour
• Design verification techniques (analytical and CFD-based)
• Integration with occupant evacuation timelines (ASET vs RSET)

Interim approaches in the UK

Until prEN 12101-12 is published, time-dependent SHEVS design in the UK is typically addressed through:

• CEN/TR 12101-5: calculation methods
• BS 7974: Application of fire safety engineering principles to the design of buildings
• The PD 7974 series of supporting published documents
• Bespoke CFD analysis where complexity warrants it

Related standards

• CEN/TR 12101-5: Functional recommendations and calculation methods
• BS 7974: Fire safety engineering principles
• PD 7974 series: Supporting published documents for fire engineering
• BS 9999: Non-residential fire safety design (use of fire engineering)

How Vent Trade can help

Vent Trade supplies certified natural and powered smoke ventilation products that integrate into time-dependent SHEVS designs. We can support fire engineers with product performance data, calculation inputs and project-specific technical advice.

Talk to our technical team →