Blog No.13-efficiency of evacuation exits

How to evaluate the efficiency of evacuation exits?

It is important to know the efficiency when designing fire protection systems. This determines how much risk could being mitigated. For passive and active protection, efficiency is usually determined by the manufacturer, or can be derived from historical data. However, for evacuation systems determining whether or not the system works is more expensive due to its interaction with people. For this reason, there is currently a method that allows the performance of an evacuation system to be measured by evaluating the capacity it offers in aspects such as sensory, cognitive, physical and functional. The method is based on the theory of affordances that allows to perform a systematic evaluation of evacuation systems. The objective of implementing this method is to identify on an early stage the flaws in the design that prevent the proper use of evacuation systems. This blog aims to show in a general way what the method consists of and how it can be applied to the evaluation of the main evacuation doors.

The first step is to evaluate the sensory aspect of the system. In other words, the evacuation door or route must be able to be felt. In general, it is expected that this is through sight, but it must be considering the reduction of the sense of sight in the middle of a fire and also taking into account people with sensory disabilities, therefore audible cues should be considered. The intention is to capture the attention of the people to evacuate. Prescriptively, codes such as NFPA define the colour, font size and location of the signage. The objective of these requirements is to find a contrast through colours, symbols, flashing lights, alarms, among others, that allow guiding people in the middle of the evacuation taking into account the darkening factor that occurs in a fire.

The second step is to evaluate the cognitive aspect. The purpose is that the people who are reading the signals or listening to a message can in an informed way act. Confusion of the message should be avoided. For example, many evacuation doors in shopping malls has signals on the evacuation exits, but an employee-only notice is posted on the door, which at the time of an emergency only creates confusion and can slow the evacuation process. Another example is the type of colour that is used. In most countries, the colour green is associated with a safe place, and the colour red is dangerous, however, in the United States, red is associated with fire systems, so a large part of its evacuation signs are red. Which would not be ideal to use in Colombia, where green has a security connotation. In conclusion, the message must be clear and conflicting messages should be avoided at all costs.

The third aspect is physical. This is related to evaluating the functionality of the systems in a physical way. For example, in the case of a door, the force required to open should not be greater than the one able to apply by an average adult. In prescriptive codes, such as NFPA 101, these requirements are clearly established. However, it is important to include people who may have any type of disability, for this reason you can also choose to install doors with panic bars, which allow doors to be opened more easily.

Finally, the functional aspect is evaluated. In other words, the element should be used for what it was designed for. For example, having an evacuation door that lead to a safe place, or having a shelter space designed so that it is possible to safely wait for rescue services. If the sensory, cognitive or physical aspect is not being met, it is determined that the functional aspect does not meet either. If it is not seen, understood or difficult to use, then the element in general cannot be used to meet the objective for the it was designed.

In conclusion, the theory of affordance helps to identify failures in the evacuation system that are inappropriate or prevent fulfilling its true function. This method allows a systematic study that examines the sensory, cognitive, physical and functional aspects of the means of evacuation.

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  1. Carattin, E.; Lovreglio, R.; Ronchi, E.; Nilsson, D. Affordance-based evaluation of signage design for areas of refuge. Interflam 2016. Fire Science and Engineering Conference, Royal Holloway College, University of London UK. 4-6 July 2016. pp. 781-786.
  2. Hartson, H.R. 2003. “Cognitive, physical, sensory, and functional affordances in interaction design. Behavior & Information Technology, 22(5):315–338

Lorena Cifuentes.
Ingeniera Química
Departamento de
Diseño EHR S.A.

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