Detection & Alarm (t_det + t_warn)
Time from ignition to detection via thermal or smoke dynamics. Warn time accounts for EWIS cascading delays.
RSET Calculator: Required Safe Egress Time
Calculate safe egress times for fire engineering. Detailed breakdown of detection, alarm, pre-travel, and movement components per ISO 13571 and PD 7974-6.
Professional Notice: Egress capabilities must be matched carefully to the specific building occupancy. RSET values must be verified by a registered Fire Safety Engineer for use in ASET vs RSET analysis.
The Components of Evacuation Timing
The Required Safe Egress Time (RSET) determines the total time required for all occupants to detect an event, recognize the alarm, gather belongings, and physically travel to a place of safety.
In a Performance Solution, the calculated RSET is heavily impacted by theDesign Fire Growth rates.It is ultimately compared against the available safe egress time to guarantee safety margins. You can explore standard methodology via ourPerformance Solutions Hub.
RSET Breakdown formula:
RSET = (tdet + twarn) + (tpre + ttrav)where:
tdet = detection time (s)
twarn = notification/alarm delay (s)
tpre = recognition and response delay (s)
ttrav = physical movement time (s)Key RSET Parameters
Pre-travel (t_pre)
Combining recognition of the cue and subsequent response. This is heavily dependent on occupant alert state (awake vs. asleep) and management structure.
Movement Time (t_trav)
The physical travel time governed by horizontal/vertical speed coefficients, specific densities, or flow pinch-points like tight stairways and narrow exit doors.
Standards & References
- AS/NZS 3745Planning for emergencies in facilities. Provides context for baseline pre-movement assumptions in the Australian jurisdiction.
- PD 7974-6British Standard publication for the application of fire safety engineering principles — Human factors.
- ISO 13571Life-threatening components of fire — Guidelines for the estimation of time to compromised tenability in fires.
Frequently Asked Questions
What does RSET mean in fire engineering?
RSET stands for Required Safe Egress Time. It represents the total duration from the moment a fire ignites to the time all occupants reach a place of safety.
How do I choose a pre-travel time?
Selection depends on the Occupant Characteristic, for example, trained staff in a warehouse would have a much lower pre-travel response factor compared to the general public in a cinema.
Does this calculator include vertical travel?
Yes, vertical evacuation dynamics can be simulated by specifying alternate flow rates or effective travel speeds for stairwells.
How does ASET compare to RSET?
ASET (Available Safe Egress Time) dictates when toxic or heat conditions escalate to an untenable level. Engineers must prove that ASET > RSET by a solid factor of safety.
Export Egress Engineering Audits
The RSET logic is highly sensitive to input variables. Ensure accuracy by exporting PDF logs that display broken-down event delays for your compliance verification packages.