No contractor may use or permit any person to use an explosive actuated fastening device, unless-
(a) the user is provided with and uses suitable protective equipment;
(b) the user is trained in the operation, maintenance and use of such a device;
(c) the explosive actuated fastening device is provided with a protective guard around the muzzle end, which effectively confines any flying fragments or particles; and
(d) the firing mechanism is so designed that the explosive actuated fastening device, will not function unless-
(if) it is held against the surface with a force of at least twice its weight; and
(ii) the angle of inclination of the barrel to the work surface is not more than 15 degrees from a right angle.