Introduction

Sampling and analysis of fire effluents is required for a variety of applications in life threat assessments^[⁴^][¹¹^][²⁶^] and environmental impact from fires assessments.^[⁶^] The end result of these analyses is a list of chemical species and their concentrations in the effluent at a specific time or over a time interval, and at a specific location, during (and possibly after) the period of generation of the effluents. Depending on the end use of these data, the requirements can range from a highly detailed, time-resolved, quantified and validated list of chemical species to a simple estimate of a single compound or small range of compounds.

Although methods used in other fields are occasionally employed (e.g. atmospheric pollution), obtaining relevant data often requires specialized sampling and analysis techniques. This is due to the complexity, reactivity and generally “hostile” nature of typical fire effluents, as well as the commonly observed rapid changes in concentrations with time and distance from the fire source.

The following typical properties of fire effluents render more “traditional” methods of sampling and analysis inappropriate:

— high temperatures of 1 000 °C or higher;
— presence of aerosols (i.e. solid and liquid particulates) with a wide range of particle sizes and distribution, together with adsorbed and absorbed chemical species;
— presence of condensable organic and inorganic vapours (e.g. water);
— high turbulence, with spatially and temporally variable concentrations;
— a very wide range of species and their concentrations, typically varying rapidly with time and location with respect to the fire source (or heating zone in the case of a “bench-top” physical fire model);
— presence of acidic/corrosive species;
— presence of water-soluble species and/or or highly reactive species resulting in sampling losses.

The identification of these factors has led to the development of new methods or the adaptation of existing methods for the sampling and analysis of the gases and vapours in the effluent from fires and physical fire tests.

Common sampling and analysis methods have emerged in recent years, and in some cases, International Standards, such as ISO 19701, have been published for selected gases and vapours. Much of this information is provided in ISO 19701, which presents a variety of methods for the sampling and analysis of individual gases of toxicological importance. Several methods are often needed to determine all the species of interest for fire hazard analysis.

Fourier Transform Infrared (FTIR) spectroscopy offers an improved procedure, principally through:

— single-method measurements of gases and vapours relevant to fire toxicology;
— time-resolved measurements over relatively short periods (i.e. concentrations of chemical species of interest), enabling the monitoring of chemical species development and decay throughout the fire or physical fire test; and
— revisiting the stored FTIR spectra to potentially obtain relevant data concerning the presence of a toxicant which is identified as important.

While ISO 19701 summarizes the technique and some applications of FTIR in fire gas analysis along with many other common methods, this document provides details of the established requirements and best practices for obtaining reliable sampling and analysis results using the FTIR method.

FTIR spectroscopy can be used to analyse fire effluents using these two methods:

a) open path analysis, where the infrared beam is directed across the effluent within and/or outside the fire test apparatus;
b) extractive analysis, where a fraction of the effluent from a fire test apparatus is drawn continuously through a heated sampling system through the gas cell of the FTIR instrument, enabling remote measurement (e.g. IMO Resolution MSC 61(67), Part 2: Toxicity analysis^[⁹^]).

Both procedures (and variants) have been successfully applied, although the extractive analysis technique is far more common in fire effluent analysis.

Of particular relevance in the development of FTIR as a practical tool in fire gas analysis is the Smoke Gas Analysis by Fourier Transform Infrared Spectroscopy or SAFIR, a European Union-funded project^[¹⁸^][¹⁹^] which focused on the testing and validation of an extractive FTIR method when used in a variety of situations. The results of the SAFIR project formed the basis of the first edition of this document (ISO 19702:2006). The second edition of this document (ISO 19702:2015) was based on subsequent updates e.g. References [8], [15], [21], [25] and [27].

Any chemical analysis is selective in terms of chemical species determined and the accuracy and precision of quantitative measurements. Some chemical analytical methods can be appropriate for accurate determination of some species but less appropriate for other species. Thus, despite the ability of FTIR spectroscopic analysis to measure a wide range of chemical species of interest in the field of life threat from fire, additional methods can also be necessary to determine all the species of interest for a particular application. However, the use of FTIR analysis alone can provide data of sufficient quality to identify and calculate the concentrations of many of the chemical species that are important in toxic hazard assessment.

ISO 19702:2024

Sampling and analysis of toxic gases and vapours in fire effluents using Fourier Transform Infrared (FTIR) spectroscopy

Current

Published:

19 Dec 2024