Time to critical condition in emergency services

TL;DR

This paper derives an explicit formula for the average time until emergency response systems reach a critical shortage, validated through simulations, aiding performance assessment of such systems.

Contribution

It provides a new analytical expression for estimating the mean time to critical system shortage in emergency services, validated with simulations for realistic scenarios.

Findings

Analytical formula approximates the mean time to critical condition effectively.

Simulation results confirm the formula's accuracy under various service time distributions.

The method aids in performance evaluation and planning for emergency response systems.

Abstract

Providing uninterrupted response service is of paramount importance for emergency medical services, regardless of the operating scenario. Thus, reliable estimates of the time to the critical condition, under which there will be no available servers to respond the next incoming call, become very useful measures of the system's performance. In this contribution, we develop a key performance indicator by providing an explicit formula for the average time to the shortage condition. Our analytical expression for this average time is a function of the number of parallel servers and the inter-arrival and service times. We assume exponential distributions of times in our analytical expression but for evaluating the mean first-passage time to the critical condition under more realistic scenarios we validate our result through exhaustive simulations with lognormal service time distributions. For this task we have implemented an simulator in $R$. Our results indicate that our analytical formula is an acceptable approximation under any situation of practical interest.