The Factories Act requires as under:
Every hoist and lift equipment shall be of good mechanical construction, sound material, and adequate strength, properly maintained and examined by a competent person at least once in every six months. Its report should be in Form No. 9, GFR.
Good construction means as per standards (BIS). Sound material means as per the required quality of the material. Adequate strength means proper design, the factor of safety and good workmanship. Properly maintained means following safe and standard procedure, work permits, manufacturers and other guidelines.
Every hoist or lift shall have the safe working load plainly marked on it and no-load greater than such load should be carried on it. The cage of every hoist or lift used for carrying persons should be fitted with a gate on each side from which access is afforded to landing and such gates should be fitted with interlocking devices to ensure that they cannot be opened except when the cage is at the landing and the cage cannot be moved unless all the gates are closed.
Whenever the cage is supported by rope or chain, there shall be at least two ropes or chains separately connected with the cage and balanced weight and each rope or chain with its attachment must be able of carrying the whole weight of the cage together with the maximum load. Efficient devices should be provided and maintained capable of supporting the cage together with the maximum load in the event of breakage of the ropes, chains or attachments. There should also be an efficient automatic device to prevent the cage from over-running.
Horsepower to lift a load is given by the following formula:
Safety in Design, Construction, and Operation of LIFT AND HOISTS
- Hoist limit switch to cut off power and apply brakes when hook/cage rises to a predetermined level to prevent over-winding.
- Limit switches to prevent over traveling and over transferring. These limit switches should automatically reset within a reasonable distance traveled in the opposite direction.
- Emergency push button for prompt use.
- Isolation switch to cut off all power except lighting. Proper earthing.
- Off position, interlocking to prevent the circuit breakers from being closed unless all controllers are in off position.
- The screen on bare conductors.
- Pilot lamp (red lens) to indicate on or off condition.
- Handlamp of 24 volt DC.
- Earthing as per Electricity Rules.
- Means of anchoring when the hoist/crane is left unattended or under storm conditions.
- Others: Sheaves guard to retain ropes in grooves, safe means of access, ladders, and guards on moving/rotating parts. Examination for wear, malfunction, damage and proper operation of hooks, ropes, brakes, clutches and limit switches.
- Safety points for operation: No loading over SWL. Marking of SWL and load indicators for varying SWL. Pick-up load only when it is directly under the hook, otherwise stresses will develop. Full vision in driver’s cabin. Fire extinguishers, warning device, safe operating precautions for raising and lowering loads, moving loads over workers working underneath and duties of drivers while leaving the cabin, should be prescribed and followed. People should not be lifted or transported by hoist or crane.
Safety Aspects of Lifting or Elevators:
Following are the specific safety aspects for safe design and operation of lifts or elevators:
- Lifts wells: No projection inside, sufficient space for repairs and maintenance, fireproof to the maximum extent.
- Lift Well Enclosures: Enclosed construction, if wire mesh, the opening should not be more than 32 mm. Clearance between moving the car and the platform sill or wall shall not be more than 25 mm to avoid trapping.
- Lift Pit: It should be waterproof to disallow water from outside.
- Top & Bottom Clearance: Minimum 1 mt in the top and 1 mt in the bottom.
- Landing Gate & Doors: Landing door should cover the full size of the car gate opening and if it is collapsible, grill opening should not be of more than 6 cms wide and if it is solid, it should have a vision panel of not more than 25.mm width. A solid door is safer.
- Interlocked Gates & Doors: Lift car shall not move until all landing doors are closed and they will not open till the car is moving, except by a special key. Automatic door-closure are useful.
- Lift Cars: Enclosed type, smooth and non-slippery floor, alarm and push-button, light, ventilation, plug-socket on car top to take power supply for maintenance work, a factor of safety more than 5, marking of ‘persons capacity’ (base 68 kg per person).
- Counter Weight: Should be in a steel frame, secured by two tie rods to prevent fall and travel in a rigid steel guide.
- Buffers: Spring or hydraulic types, of adequate strength, on the pit floor to absorb shocks if the car falls.
- Suspension Rope: 3 independent ropes for traction drive and 2 ropes with drum drive each rope separately and independently fixed to car and counter-weight, ropes free from joints and factor of safety more than 12 based on static count load + weight of car and accessories.
- Emergency Safety Device: Safety gear-Instantaneous type, Gradual Wedge clamp or Flexible guide clamp-to retard the speed if it exceeds 1 m/s and operating on both the guides.
- Over Speed Governor: It prevents the car from falling or overspeeding downwards. If the speed exceeds the normal design speed, the governor applies brakes on the car driving mechanism and also releases safety clamps against the guide rails to bring the car to a smooth sliding stop.
- Slack Rope Switch: If the car is obstructed while descending and the rope becomes slack, this switch will stop the machine.
- Machine Room: Height should be more than 2 m, space around m/c more than 60 cm, hand lamp provided and room locked with a key, with the authorized person.
- Machine Supports: Supporting beams shall be of steel or RCC. The factor of safety shall be 5 for steel and 7 for RCC.
- Final Limit Switches: Upper and lowers ultimate switches to stop the car automatically within the top and bottom clearances in independently of the normal operating device and the terminal limit switches.
Testing Inspection and Maintenence
Testing includes insulation tests for electric wiring. Test voltage should be DC (more than twice the rated voltage) and insulation resistance of each wiring circuit should be more than 2 m ohms.
Tests for satisfactory operation of each controller, switch, contactor, relay, interlocks, the sequence of operation, protective devices. Tolerance on specified speeds at full load shall be within 10%.
Overload test by 125% of the working load. Proof (test) load may vary from 1.5 to 4 times of the SWL.
Periodic inspections to detect unsafe conditions, warm or damaged parts, wear and other defects in wire and fiber ropes, lifting gear, tires, etc. are necessary.
Gear wheels and pinions should be maintained in good condition, properly keyed and in their correct gear mesh. Gear wheels and pinions with broken teeth or cracked areas, rims or bosses should be discarded and replaced. The faces of all ratchets, jaw clutches, gear locks, and collars should be kept in their correct relationship to ensure safety in use.
Repairs shall be carried out by ‘permit to work‘ system. All power shall be disconnected while doing such work.
Notices like ‘under repair’ out of order don’t start etc. shall be displayed.