Section 27-704. Equipment

(a) General. The hammer shall travel freely in the
  leads.  The  cushion  or  cap  block  shall be replaced, if crushed. The
  hammer shall deliver its rated energy, and measurements shall be made of
  the fall of the  ram  or  other  suitable  data  shall  be  observed  at
  intervals  as  required  to  verify  the  actual energy delivered at the
  termination of driving.
    (b) Cushion or cap block. The cushion or cap block shall  be  a  solid
  block  of  hardwood with its grains parallel to the axis of the pile and
  enclosed in a tight-fitting steel housing, or  shall  be  an  equivalent
  assemblage.  If  laminated materials are used, the type and construction
  of these materials shall be such that their strength  is  equal  to,  or
  greater  than,  hardwood. Wood chips, pieces of rope, hose, shavings, or
  automobile tires and similar materials shall not  be  used.  Cap  blocks
  shall be replaced if burned, crushed, or otherwise damaged.
    (c) Followers. Followers shall not be used unless permitted in writing
  by the architect or engineer, and only when necessary to accomplish such
  installation.  They  shall  be of steel or hardwood of such size, shape,
  length, and weight as to permit driving the pile in the desired location
  and  to  the  required  depth  and  resistance.  The  required   driving
  resistance  tabulated  in  Tables  11-4  and  11-5 shall be increased to
  compensate for the loss of energy in the hammer blow. The follower shall
  be a single length section, shall be provided  with  a  socket  or  hood
  carefully  fitted  to the top of the pile to minimize loss of energy and
  to prevent damage to the pile, and shall  have  sufficient  rigidity  to
  prevent "whip" during driving.