Fire behaviour of twisted pair communication cables

• Thermal and elemental analysis of PVC, PE, LSZH and LSZHFR cable sheaths was performed. • FTIR confirmed HCl release in PVC even at low decomposition temperatures. • Firefighting wastewater from PVC showed the highest toxicity to Vibrio fischeri. • LSZHFR cables exhibited the lowest ecotoxicity and superior fire safety. • All tested cable runoff samples were classified as hazardous property HP14. Unshielded twisted pair (UTP) cables are ubiquitous in modern building infrastructures; however, the multifaceted risks associated with their combustion remain insufficiently addressed. This study provides a comprehensive assessment of Category 6 UTP cables (PE, PVC, LSZH, and LSZHFR) using cone calorimetry, FTIR spectroscopy, and ecotoxicological bioassays. Calorimetric results revealed significant differences in fire load, with Total Heat Release (THR) values ranging from 123.95 MJ·m⁻² for PE to 76.58 MJ·m⁻² for LSZH cables. The environmental impact was quantified through ecotoxicity assays of simulated firefighting wastewater. Bioassays using Vibrio fischeri demonstrated high toxicity across all samples, with PVC cables exhibiting the most severe impact (EC₅₀ of 29.51 mL·L⁻¹ after 30 minutes). In contrast, assays with white mustard ( Sinapis alba ) showed no significant inhibition; instead, hyperstimulation (up to 81.93% for PE) was observed at high concentrations, suggesting a high inherent resistance of seeds to firefighting wastewater contaminants. Based on the bacterial response, all tested cable runoff met the criteria for the hazardous property HP14 (Ecotoxic) according to Decree No. 8/2021 Coll. These findings underscore that UTP cable fires pose a dual threat: substantial thermal release and critical aquatic toxicity, necessitating the integration of ecotoxicological metrics into building fire safety standards.