Hazard Level (HL1, HL2, HL3)

Also: HL1, HL2, HL3, EN 45545 hazard level

EN 45545-2 hazard levels for railway interior materials. HL1 = low risk (conventional vehicles, short tunnels), HL2 = medium (longer tunnels, underground), HL3 = highest (double-deckers, underground rolling stock with complex evacuation).