Flame spread on bunched cables (IEC 60332-3, and EN 50399 where CPR heat and smoke measurement is required) decides how a cable run behaves in a tray. Circuit integrity (IEC 60331, BS 6387) decides whether a life-safety circuit keeps working through the fire. Smoke density (IEC 61034, in the smoke family) decides whether people can see to escape. A complete cable laboratory runs all three.