Slow (0.003 kW/s²)
Densely packed configurations such as tightly bound paper or dense timber stacks yielding slow flame spread.
HRR Plotter: t-Squared Design Fire Generator
The Heat Release Rate (HRR) curve is the principal driver of fire severity. Build parameter-driven design fire arrays ready to serve as sources in advanced gas and thermal models.
Professional Notice: Design fires dictate all downstream tenability results. Generating appropriate severity curves is the core responsibility of the Fire Safety Engineer in verifying life safety configurations.
The Physics of Heat Release Rate
The Heat Release Rate (HRR) determines the speed of smoke layer descent, peak ceiling jet temperatures, and the severity of structural impacts over time. Most Performance-Based design methods assume a theoretical growth arc commonly referred to as a t-squared curve.
You can utilize t-squared HRR curves as direct source terms for ourSmoke Filling Analysis calculation. By properly correlating peak steady states and decay limitations, engineers cap severity appropriately based on available air limits context.
t-Squared Base Formula:
Q = α · t2where:
Q = calculated heat release rate (kW)
α = fire intensity growth coefficient (kW/s²)
t = time from established ignition (s)Alpha Growth Rates by Material
Medium (0.012 kW/s²)
Standard commercial footprints including loose cotton pillows, mattresses, and typical office furniture configurations.
Fast (0.047 kW/s²)
High stacks of cardboard cartons, lightweight packaging arrays, and scattered non-dense combustibles.
Ultra-Fast (0.188 kW/s²)
High-volatility arrays, polyurethane foams, and uncontained flammable liquid pools burning cleanly in air.
Standards & References
- SFPE HandbookIncludes vast reference arrays determining fuel alpha ranges based on full-scale experimental validations.
- NFPA 92Standard for Smoke Control Systems — heavily defines design fire boundaries for extracting mass-flows.
- DrysdaleAn Introduction to Fire Dynamics — fundamental theoretical text outlining stoichiometric burn limits.
Frequently Asked Questions
What is a t-squared (Q=αt²) fire curve?
The t-squared fire model is a widely used approximation for the growth phase of a fire. It assumes that the heat release rate increases proportionally to the square of time.
What is the fire growth alpha factor?
Alpha is the fire intensity coefficient expressed in kW/s². Common baseline limits follow standard experimental clusters ranging from Slow to Ultra-Fast severity patterns.
Can I export the data plotted?
Yes, curves and data-points built using this module are exportable as CSV/Text arrays which enable easy mathematical transposition into Zone or CFD software.
What limits the peak HRR?
Generally, peak HRR is constrained either by the available floor area of the fuel array itself or the available air oxygen limit within the room (otherwise known as being ventilation limited).
Generate Exportable Design Curve Profiles
Build your required data structures instantly. Every plotted matrix generates an exportable CSV bundle ready to be dropped into structural or environmental assessment matrices.