Regulation (EU) No 305/2011 lays down harmonized conditions for marketing construction products in the European Union. One of its consequences has been the introduction of the product standard EN 50575 and standard EN 130501-6, concerning power, control, and communication cables permanently installed in buildings to prevent the risk of a fire and its consequences. EN 13501-6 provides the reaction to fire classifications for cables, the test methods to be performed, the requirements to meet a specific reaction to fire, and additional classifications for smoke production, flaming droplets, and acidity. EN 60754-2 is the technical standard used to assess acidity, and it defines three classes: a1, a2, and a3 (the less performant), based on pH and conductivity measurements. Due to the release of hydrogen chloride during the combustion, acidity is the weak point of PVC cables, which are not yet capable of achieving the a1 or a2 classes required in specific locations according to a fire risk assessment. EN 13501-6 does not include EN 60754-1. Both EN 60754-1 and EN 60754-2 are common standards for determining halogen gas content, acidity, and conductivity, respectively. They involve the same type of tube furnace but with different heating regimes, final temperatures, and detection methods. EN 60754-2 must be performed at temperatures between 935 – 965 °C. The paper demonstrates that, when EN 60754-2 is carried out with the thermal profile of EN 60754-1 or at 500 °C in isothermal conditions, the evolution of hydrogen chloride changes significantly if potent acid scavengers are utilized in the PVC compounds. The reason lies behind the kinetic of hydrogen chloride release during the combustion of PVC compounds: the higher the temperature or faster the heat release, the quicker hydrogen chloride evolution and the lower the probability for the acid scavenger to trap it. That further highlights the "fragility" of EN 60754-2 as a tool for assessing the risks associated with the release of hydrogen chloride in case of fire

The combustion of PVC cables in fires results in the release of hydrogen chloride gas. In the European Union, Regulation (EU) No 305/2011, in force since 2017, requires the classification of cables permanently installed in buildings for reaction to fire, smoke, flaming droplets, and acidity. The additional classification for acidity is evaluated through EN 60754-2, involving pH and conductivity measurements. This study focuses on the essential research and development of low-smoke acidity PVC compounds for cables, mainly aiming to meet the stringent additional classifications for acidity, a1 or a2, which cannot be achieved with traditional PVC cables. Understanding the chemistry of thermal decomposition and combustion, especially in the presence of hydrogen chloride scavengers, is crucial for meeting the best acidity classification. The article reviews the current tube furnace tests used in the European Union for cable halogen and acidity assessments. It discusses the limitations of the existing method (EN 60754-2) and highlights the potential of emerging tests such as IEC EN 60754-3, which employs ion chromatography for improved sensitivity and specificity. In the experimental part of the article, various standard and low-smoke acidity cable compounds are tested using tube furnace experiments with different heating regimes. The concentrations of cations and anions in solution are measured through ion chromatography and inductively coupled plasma–optical emission spectrometry. This detailed analysis aims to identify the species influencing pH and conductivity, which is crucial for designing effective acid scavengers that do not impact conductivity. The conclusive results emphasize that HCl from PVC thermal decomposition is the primary driver of pH and conductivity, and the contribution from the decomposition of additives and byproducts from combustion is found to be negligible in most of the tested PVC compounds for cables. The findings underscore the importance of understanding the thermal decomposition of PVC compounds to design acid scavengers capable of trapping hydrogen chloride without adversely impacting conductivity.

In PVC compounds, hydrogen chloride plays a fundamental role in .H and .OH radical trapping lowering the flame energy during combustion. Furthermore, it yields actual Lewis acids promoting the cross-linking of the polyene sequences from PVC degradation and bringing a char layer, protecting PVC items from flames. Therefore, PVC is inherently flame retarded. However, plasticized PVC requires flame retardants and smoke suppressants to enhance fire performance. Low smoke acidity PVC compounds contain potent acid scavengers capable of acting at high temperatures. They react with hydrogen chloride in the condensed phase, making it unavailable in the gas and even in the condensed phase, compromising the reaction to fire and enhancing the smoke produced during the combustion. The effect of the sequestration of hydrogen chloride in PVC compounds for cables by potent acid scavengers has been studied in this paper through measurements of oxygen index, heat release, and smoke production. It is shown that potent acid scavengers strongly affect parameters like fire growth rate in cone calorimetry, specific (total) heat capacity, and specific heat of combustion of fuel gases in micro combustion calorimetry. They neutralize the action of antimony trioxide and Lewis acid precursors commonly used as flame retardants and smoke suppressants in PVC items, making them prone to ignite, release smoke, and spread flame. A new generation of flame retardants and smoke suppressants is necessary to keep low smoke acidity and high fire performances together in PVC items