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SECTION 5. RESPONSE TIME ANALYSIS
Response times are typically the primary measurement for evaluating fire and EMS services. Most
deployment models have been built around a four-minute initial travel time for EMS and an
eight-minute full-force travel time for fires. Though these times have validity, the actual impact of
a speedy response time is limited to very few incidents. For example, in a full cardiac arrest,
analysis shows that successful outcomes are rarely achieved if basic life support (CPR) is not
initiated within four minutes of the onset. However, cardiac arrests occur very infrequently; on
average they are 1 percent to 1.5 percent of all EMS incidents.
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There are also other EMS
incidents that are truly life-threatening and the speed of response can clearly impact the
outcome. These involve full drownings, allergic reactions, electrocutions, and severe trauma
(often caused by gunshot wounds, stabbings, and severe motor vehicle accidents, etc.). Again,
the frequencies of these types of calls are limited.
Regarding response times for fire incidents, the criterion is based on the concept of “flashover.”
This is the state at which super-heated gasses from a fire are released rapidly, causing the fire to
burn freely and become so volatile that the fire reaches an explosive state. In this situation,
usually after an extended period of time (often eight to twelve minutes after ignition but times as
quickly as five to seven minutes), and a combination of the right conditions (fuel and oxygen),
the fire expands rapidly and is much more difficult to contain. When the fire does reach this
extremely hazardous state, initial firefighting forces are often overwhelmed, larger and more
destructive fire occurs, and significantly more resources are required to affect fire control and
extinguishment. Flashover has been observed to occur more frequently today due to greater
quantities of plastic- and foam-based products in homes and businesses. These materials ignite
and burn quickly and produce extreme heat and toxic smoke. Figure 5-1 illustrates the flashover
phenomenon and its potential impact on firefighters and fire extinguishment as the fire
propagation curve.
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Myers, Slovis, Eckstein, Goodloe et al. (2007). ”Evidence-based Performance Measures for Emergency
Medical Services System: A Model for Expanded EMS Benchmarking.”
Pre-hospital Emergency Care.