Aim: The purpose of the article is to present issues associated with intelligibility of voice messages broadcast by voice alarm systems during emergencies in buildings. Particular attention was paid to the choice of appropriate method for measurement of speech intelligibility and identification of differences between methods.

Introduction: Voice alarm systems are used as tools, to assist rescue operations with the evacuation of buildings during emergencies, e.g. during an outbreak of a fire. It is also possible to use such systems for non-emergency purposes e.g. advertising, information about approaching trains, or music. Speech intelligibility is a very important parameter, which determines the quality and effectiveness of communication. The voice alarm system, when properly designed and installed, should broadcast information, which should be understood during an evacuation process. There are several methods, which can be used to verify speech intelligibility; objective (used more often) and subjective. The decision concerning choice of method is very important and, sometimes during the measurements process, it may be necessary to change to an alternative, e.g. when a building and/or voice alarm system do not meet specified parameters.

Methodology: The study contains a critical review of literature and includes outcomes from observation. Normative documents, describing the process of designing and installation of voice alarm systems, were analyzed. Additionally, the author’s experience with systems across a range of installations were harnessed.

Conclusions: This article revealed results from an analysis of literature, normative documents and authors experience in the design and installation of voice alarm systems in buildings. The analysis leads to following conclusions: – Speech intelligibility is affected by system components (amplifiers, speakers) and room acoustics (reverberation time, noise, furnishing). – The most common method of measurement is with the aid of a Speech Transmission Index (STI) or its simplified version Speech Transmission Index for Public Address Systems (STIPA). – It is necessary to standardise the design and installation requirements for voice alarm systems, including measurement of speech intelligibility. – Certification of services should be considered for business concerns engaged with the measurement of speech intelligibility because, currently, there is a lack of any requirements in this area.

Keywords: voice alarm systems, measurements of speech intelligibility

Type of article: review article