Raising   of   large   form   panels   should   not   be attempted in heavy gusts of wind, neither by hand nor by  crane. Skip loader cables and brakes must be inspected frequently to prevent injuries caused by falling skips. The  mixer  operator  must  never  lower  the  skip without first ensuring there is no one under it. The area around the mixer must be kept clear. Dust protection equipment must be issued to crew members engaged in handling cement, and they must wear the equipment when so engaged. Workers should stand with their backs to the wind, whenever possible, to prevent cement and sand from being blown into their eyes and faces. Whenever  the  mixer  drum  is  being  cleaned,  the switches  must  be  open,  the  throttles  closed,  and  the control mechanism locked in the OFF position. Whenever   possible,   a   flagman   or   watchman should be stationed near the mixer to warn all hands when  a  batch  truck  is  backing  up  to  the  skip.  The watchman should use a whistle to warn any personnel in the danger zone. “DANGER-KEEP AWAY” signs should be placed where they can readily be seen. FORMWORK FORMWORK  is  a  temporary  structure  that supports its own weight and that of the freshly placed concrete as well as the live loads imposed upon it by materials,   equipment,   and   workmen.   As   a   Builder serving  in  the  capacity  of  a  form  designer  or  as  the supervisor  of  a  form  building  crew,  you  should  take into account the three principle objectives when using formwork—economy,  quality,  and  safety. Economy  is  the  major  concern  since  formwork may represent as much as one third of the total cost of a concrete structure. Savings depend on the ingenuity and   experience   of   the   formwork   designer   or supervisor. Judgment in the selection of materials and equipment,   in   planning   fabrication   and   erection procedures,  and  in  scheduling  reuse  of  forms  will expedite  the  job  and  help  reduce  formwork  costs.  In designing and building formwork, you should aim for maximum   economy   without   sacrificing   quality   or safety.   Shortcuts   in   design   or   construction   that endanger quality or safety may be false economy. For example,  if  the  forms  do  not  produce  the  specified surface finish, much hand rubbing of the concrete may be required; or if forms deflect excessively, bulges in the   concrete   may   require   expensive   chipping   and grinding.  Obviously,  economy  measures  that  lead  to formwork  failure  also  defeat  their  own  purpose.  The most commonly used form materials are earth, metal, lumber, plywood, and fiber. FORM DESIGN Forms must be designed for all the weight to which they are liable to be subjected, including the dead load of  the  forms,  the  plastic  concrete  in  the  forms,  the weight of crew members, the weight of equipment and materials that may be transferred to the forms, and the impact due to vibration. These factors vary with each project,  but  none  should  be  neglected.  Ease  of  erection and   removal   are   also   important   factors   in   the economical   design   of   forms.   Platforms   and   ramp structures  independent  of  formwork  are  sometimes preferred   to   avoid   displacement   of   forms   due   to loading  and  impact  shock  from  crew  members  and equipment.  Formwork  for  concrete  must  support  all vertical  and  lateral  loads  that  may  be  applied  until these  loads  can  be  carried  by  the  concrete  structure itself.   Loads   on   the   forms   include   the   weight   of reinforcing steel and fresh concrete, the weight of the forms  themselves,  and  various  live  loads  imposed during  the  construction  process.  Consideration  must be  given  to  such  conditions  as  unsymmetrical placement of concrete, uplift, and concentrated loads produced  by  storing  supplies  on  the  freshly  placed slab. Rarely will there be precise information as to the loads the formwork maybe subjected to; therefore, the architect or Builder must make some safe assumptions that   will   hold   good   for   conditions   generally encountered. Vertical  Loads Vertical loads on formwork include the weight of reinforced  concrete  together  with  the  weight  of  the forms themselves, which are regarded as dead loads, and the live loads imposed by the crew members and the equipment used during construction. The majority of   all   formwork   involves   concrete   weighing   150 pounds per cubic foot. Minor variations in this weight are not significant, and in most cases, 150 pounds per cubic  foot,  including  the  weight  of  the  reinforcing steel,  is  commonly  assumed  for  design.  Formwork weights vary from as little as 3 or 4 pounds per square foot (psf) to 10 to 15 pounds per square foot. When the frame work weight is small in relation to the weight of the   concrete   plus   the   live   load,   it   is   frequently neglected.  If  concrete  weighs  150  pounds  per  cubic foot, it will place a load on the forms of 12.5 pounds per square foot for each inch of slab thickness. Thus a 3-2