The invention relates to a method of preparing a composition of living polymers comprising a non-photoinitiated radical polymerization step using a composition consisting of: at least one ethylenically unsaturated monomer, preferably a methacrylic monomer, at least one disulphide compound having formula, i. One or more sensors coupled to the safety harness sense tension therein and generate a signal indicative of the tension. A friction clutch mechanism includes a pair of outer stationary plate members, a pair of movable plate members, a pair of inner stationary plate members having an inner surface which is tapered at an angle of approximately 4.