Fractional Effective Dose (FED)
Definition
A physiological model that combines exposure to CO, HCN, CO2, reduced O2, and heat into a cumulative incapacitation estimate. Used with FDS outputs to determine when an occupant at a specific location would have been incapacitated or could no longer escape.
- Combines exposure to
- CO, HCN, CO2, reduced O2, heat
- Output
- Cumulative incapacitation estimate
- Used with
- Fire Dynamics Simulator (FDS) outputs
- Application
- Occupant escape/survivability timing
Common questions
Why does FED combine multiple toxic gases instead of evaluating carbon monoxide alone?+
Fire smoke rarely contains a single incapacitating agent; CO, HCN, and reduced oxygen act together and can have combined or synergistic effects on the body, so summing fractional contributions from each gives a more realistic estimate of when a person becomes unable to escape than any single gas threshold.
How is FED used to reconstruct whether a fire victim could have escaped?+
Investigators combine FDS-modelled gas concentrations at the victim's location over time with the FED model to estimate the point at which cumulative toxic exposure would have caused incapacitation, then compare that time against the estimated time available for escape.
What is the difference between the FED reaching 1.0 and actual death occurring?+
An FED value of 1.0 represents the modelled threshold for incapacitation, the point where escape is no longer physically possible, not necessarily death itself; death can follow afterward from continued exposure, thermal injury, or a combination of factors once escape is no longer an option.
Related terms
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