This fall arrest block comprises of a retractable lifeline made of 4.8mm wire rope which is stored on a reel within a protective housing. The reel is spring-based to wind the retractable lifeline in. The reel incorporates an inertia brake mechanism which allows the lifeline to be slowly extracted and automatically retracted to accommodate the user???s body movements. It also comprises of a swivel snap hook with a double safety lock and fall indicator.