Assessment of the impact of fire retardants on the combustion of natural polymers employing DTG and LOI D. S. Bakirtzis 1, * ,† , V. C. Tsapara 2 , K. G. Kolovos 3 and S. E. Liodakis 2 1 Fire Dynamics and Materials Laboratory, Fire Safety Engineering Research and Technology Centre (FireSERT), School of the Built Environment, University of Ulster, Jordanstown campus, Shore Road Newtownabbey, Co. Antrim, BT370QB Belfast, Northern Ireland UK 2 Laboratory of Inorganic and Analytical Chemistry, School of Chemical Engineering, National Technical University of Athens (NTUA), 9 Iroon Polytecniou Street, Athens 15773, Greece 3 Division of Physical Sciences and Applications, Laboratory of Inorganic Chemical Technology, Hellenic Army Academy, Vari 16673, Greece SUMMARY Thermal analysis is widely used for the investigation of the thermal decomposition of polymeric/lignocellulosic materials. Differential thermogravimetry (DTG) curves have been used for the assessment of fire retardants employing a mathematical technique, based on the observation that the DTG profile peaks become less pro- nounced and are shifted to lower temperatures when a fire retardant is added. The efficiency of a fire retardant is proposed to be assessed from a formula comprising of the following: (i) the depth of the main peak; (ii) the main decomposition peak temperature; (iii) the temperature range of the DTG curve; and (iv) the area above the curve. Initially, four well-known fire retardants have been assessed for their efficiency on a lignocellulosic matrix (Olea europaea). All the results deriving from the mathematical technique have been compared with the mass residue criterion and a limiting oxygen index test (Relative Limiting Oxygen Index). Both are commonly used as reliable tools for the assessment of a fire retardant. Secondly, the impact of fire retardant concentration on efficiency was investigated. In addition, using mathematical routines, an optimum concen- tration zone was proposed; further, an optimum concentration value (%) has been estimated. Copyright © 2014 John Wiley & Sons, Ltd. Received 22 July 2013; Revised 25 November 2013; Accepted 2 January 2014 KEY WORDS: TGA; DTG; RLOI; mass residue; fire retardants; efficiency assessment 1. INTRODUCTION Polymers (synthetic or natural) are highly combustible because of their chemical structure, made up mainly of carbon and hydrogen. Forest species (f.s.) mainly consist of natural polymers (hemicelluloses, cellulose, and lignin). As they are highly combustible, they are frequently implicated in forest fires, causing fatalities and disasters of high financial cost. Fire retardants (F.Rs) play an important role in the suppression of forest fires as they maximize the fire suppressant capacity of water. The impact of each FR’s action can be observed at one or more steps of the polymer’s thermal decomposition (i.e., pyrolysis, ignition, gas-phase combustion, etc.). Acting physically (by cooling, fuel dilution, etc.) or chemically (reaction in the solid or gas phase), they decrease the flame spread, the heat release rate, and the quality/quantity of flammable emitted gases. Concerning forest fires, a factor that influences the effectiveness of a fire-extinguishing operation using chemical additives is the concentration of the product applied. It is important *Correspondence to: D. Bakirtzis, Newtownabbey, School of the Built Environment FireSERT, University of Ulster, Co. Antrim, BT370QB Belfast, Northern Ireland, UK. † E-mail: d.bakirtzis@hotmail.com Copyright © 2014 John Wiley & Sons, Ltd. FIRE AND MATERIALS Fire Mater. 2015; 39:109–118 Published online 6 February 2014 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/fam.2232