© 2009 Er. Jagvir Goyal
Note: This highly informative and elaborate paper was written by the Author many years back and holds valuable information. Readers should update themselves with the latest developments that might have occurred after the presentation of this paper.
Construction works are dangerous by nature itself. Many risk factors are involved; many agencies are working together whose coordination is important to ensure safety during construction. The complexity of the work, mounting pressures to achieve the targets and most of the labour being illiterate and unaware of safety steps, makes it impossible to eliminate accidents during construction. That’s why, all around the world, more people die at construction works than in road accidents. Yet it is quite possible to minimize the number of accidents during construction by using safe equipment and by taking some effective steps based on actual experience in construction sector.
The awareness: More and more people are becoming aware of the importance of safety in construction sector. In October, 2004, biggest ever campaign was launched in Europe to make engineers, builders and workers aware of the importance of safety during construction. Electrocution, falling from heights and getting crushed under machinery were noted to be the three major causes of accidental deaths during construction. In India, the scene is somewhat different. Indian construction industry is still highly labour intensive. Till a few years back, use of machinery was considered by the builders as costlier than employing labour which was available at cheap rates due to unemployment and poverty. Now the scene is undergoing a change and more of machinery is being used at sites. The reasons behind most of accidents during construction in India has therefore been the failure of scaffolds, falling from heights and getting buried in excavated pits due to collapse of improperly cut earth walls.
Safety steps: While trying to enlist steps for safety in construction, many of them, useful to enforce safety in construction and to eliminate fatal accidents occur in mind. Most of these are based on actual experience in the field. These are:
1. Ensure that all scaffolds are safe. Get them designed rather than leaving them to foreman’s experience. Decide the spacing of verticals, horizontals and braces carefully. Prefer steel scaffolds to wooden scaffolds.
2. Make safe access arrangements. Wherever motor run passenger cages are used to transfer people to the top of buildings, take special care of wire ropes and the hoists. Maintain them well and allow none to fail.
3. Wherever the height of building crosses 30 metres, provide temporary lightening protection arrangement. Also provide temporary aviation warning light arrangement to send a signal to the air-crafts flying overhead. Allow these to remain in position till permanent arrangements are provided in the buildings.
4. Take adequate measures against fire. Keep gas cylinders upright. Train some workers in use of fire extinguishers and other equipment.
5. In multi-storey buildings, make the use of safety helmets and safety belts compulsory and allow no worker to enter the work area unless he wears these.
6. Provide warning signs around the construction area. Let these scream: Men working overhead! Danger, winch area ahead!! Blasting in progress!!! etc.
7. Always keep first aid box at site and keep it updated. Always keep a standby vehicle at site to rush an injured worker to hospital. Those few moments saved are always precious.
8. Always insulate all electric tools and train workers in using insulating gloves and tools.
9. Provide sufficient illumination of work area if work is in progress at night. Provide emergency lights to avoid panic and stampede during power failures in a building under construction.
10. Always stack the excavated earth away from the pit so that it doesn’t make the sides collapse and bury the workers inside. Keep the excavated sides as sloping not vertical.
11. Create safety cells at sites whose exclusive job should be to ensure implementation of safety steps and to keep making site staff aware of the importance of safety. This cell should observe safety weeks and institute safety awards to encourage the workers.
12. Evolve a construction safety manual which should come handy at construction sites. It will save the trouble of referring to so many codes and guidelines lying scattered in different volumes but never available in time.
13. Organizations should enforce yearly safety audit of their sites by internal as well as external agencies.
Equipment for safety: As the above steps describe, use of safety equipment plays a significant role in avoiding the accidents and converting fatal accidents into non-fatal accidents. Every engineer should therefore be fully conversant with safety equipment. However, it has been noted that only scattered information is available on this topic. Our endeavour is to compile all this information here in one piece for engineers to keep it handy and use it when required.
Scaffolding pipes, clamps, joint pins and base plates: Most important factor in construction of structures is to have safe scaffolds. In high rise structures, it assumes more significance. As a high rise structure progresses skywards, work-enabling-scaffolding is raised inside and around it to enable the workers to fix the form work, bind reinforcement, lay concrete and carry out other miscellaneous jobs at the top level. It has been seen that most of the accident occur due to the failure of this scaffolding leading to a number of casualties besides complete stoppage of work. Studies of the scaffolding failures that occurred around the world and thus, the steps to be taken to avoid any such accident are as under:
a) For high rise structures, the scaffolding should be designed by the engineer instead of leaving it to the foreman’s experience. During the construction of 220 metre high RCC chimney, the spacing of the verticals below the beams was initially kept as 900 mm c/c. It was decided to check the actual load per vertical. It was found by the designer that the load per vertical exceeds its load carrying capacity and the spacing had to be reduced to 600 mm c/c. As the height of verticals increases continuously in high rise structures, it is always safe to go for proper design of scaffolding and to provide the spacing of verticals, horizontals and bracings accordingly.
b) The vertical and load bearing heavy duty scaffolding pipes need to be segregated from the horizontal and diagonal bracing pipes and marked with a red band for easy identification. These pipes should have perfect ends, no distortions or dents for full transfer of the load to the ground. The site supervisor should take care that only such pipes identified are used as ‘verticals’.
c) Separate stacks of load bearing and non-load bearing pipes should be maintained at site.
d) The clamps used for the upward extension of pipes and for fixing of horizontal and diagonal pipes to the verticals should be checked in advance, made functional and lubricated well. Defective clamps should be rejected or sent for repairs. Workers do not have the patience to check the workability of clamps and fix up whatever clamp comes to their hands. Defective clamps do not allow full transfer of load at joints.
e) Sufficient quantity of clamps should always be made available at sites of work. A shortage of clamps is an usual feature at a site of work as the number of clamps required runs into lakhs. During the studies, it was revealed that a scaffolding tower inside a cooling tower collapsed when it had reached a height of 90 metres leading to a number of casualties. The reason was found as the shortage of clamps. The workers deployed on the raising of the scaffolding tower were working on contract basis. As the clamps were not available, they kept removing the clamps from the structure below and used them to raise further height without understanding its grave consequences. Ultimately the pipes below buckled leading to the collapse of the full tower.
f) Spacing of vertical pipes needs to be decided depending upon the load to be transferred to the ground. Spacing of horizontal pipes should not be more than 1.5 metres. Diagonal braces should be provided both in horizontal as well as vertical planes.
g) Base plates should be provided below the verticals to allow sufficient bearing area for each vertical. The couplers or joint pins used for connection of vertical to vertical should be carefully designed for full transfer of load.
Access equipment: Use of safe access equipment to reach the top and working deck of a structure is another important measure for prevention of accidents during construction of structures. In general, an access tower carrying ladders to the top is provided and raised along with the gained height of a structure. In addition, a temporary cage operated by a friction hoist is provided for the engineers and supervisory staff to allow quick access to the top. During the construction of 220 metres high RCC chimney, the temporary cage fell down from a height of 20 metres to the platform at 9.00 metre level leading to suffering of multiple injuries by the supervisory staff being carried in it. The cause ascertained was snapping of strands of the wire rope used in the friction hoist besides the overloading of the cage. New wire ropes of sufficient diameter were then used and overload timer was fixed in the cage to avoid a mishap in future.
Self propelled ariel work platform equipment: Running of the hoist-operated temporary cage in an extended section of the access tower produces a lot of vibrations in it. In case such an arrangement is made, the tower should be designed and strengthened accordingly. Otherwise, for a height of 20 metres or less, self propelled ariel work platform equipment can be used. This equipment can be used even in most restricted areas of work. This equipment has articulated booms which can move a platform of 1 tonne capacity. Escorts equipment has a chassis width of only 1.2 m to 1.75 m and is fitted with all protective devices.
Friction hoists: The friction hoists used for operating the temporary cage should be well maintained to avoid its failure. Its magnetic brake should be checked every day for being effective. Preferably a double drum winch with double wire rope, each having minimum 16mm diameter should be used. The wire ropes should be checked and lubricated at regular intervals. In case any broken strands are noted, the wire rope should be replaced immediately.
Passenger cages: The passenger carrying cage used in the work should always be provided with an overload timer. In addition, it should have provisions for slow but smooth lowering of cage under gravity, for use in case of power failure. As the height of the structure and the access tower gets raised with the progress of work, arrangement should be made at the hanging point of the cage to stop it as soon as it reaches the maximum height by providing an upper limit switch.
Safety equipment: It means the equipment for the safety of workers. Important safety equipment can be enlisted as under:
1. Safety helmets: Safety helmets should always be ISI marked. All workers should compulsorily be made to wear safety helmets irrespective of their working level i.e. ground level or higher levels. It has been seen that the workers normally don’t find it convenient to wear the helmet when working. They take off their helmets and hang them aside once they are allowed entry to the working area. Such a tendency should be curbed as the workers become habitual of working with helmets on after a few days working.
2. Safety belts — All the workers deployed at higher elevations should be made to wear safety belts to avoid their falling down due to taking of a false step or slipping down etc.
3. Protective gloves, shoes and aprons: The workers handling electric equipment and chemicals should be made to wear protective gloves, shoes and aprons.
4. Ear plugs: Ear plugs should be provided to workers deployed in high noise level locations.
5. Face Masks — Face masks or nose filters should be worn by workers in areas where obnoxious gases are released by chimneys or chemical plants. Respiratory equipment should also be kept available for use when required.
6. Safety goggles: Safety goggles and flash shields should be used by workers engaged in welding work.
7. Breathing air hoods: Breathing air hoods should be provided to workers doing sand blasting or spray painting work.
8. Reflective jackets and traffic cones: These should be provided to workers engaged on highways to protect themselves from fast moving traffic.
9. Head lamps and smoke cutter lamps: These should be provided to the workers working in mines, smoke raising areas, coal handling plants, tunnels and other sub-ground works.
10. First aid box: A first aid box should always be provided at site and on all working levels in high rise structures.
11. Emergency lights: These should always be kept in enclosed areas and on all working levels to avoid panic among workers during power failures.
12. Safety mesh: At higher elevations, when working decks are to be created on the outer surface of the structure, nylon mesh should be provided covering the outer hanging scaffolds and the working decks. This mesh proves very effective in protecting the workers & preventing the goods from falling down. A similar mesh should be provided on the inner surface also if the workers have been engaged there.
Aviation warning light equipment: When the height of a structure crosses 30 metres, it has to be provided with sufficient number of aviation warning lights having a minimum intensity of 100 lux and having red colour to provide clear signal to the aircrafts flying overhead about the existence of the structure and to avoid any accident. The arrangement has to continue till the provision of permanent aviation warning lights on the structure.
Fire fighting equipment: Every construction site must be equipped with full fire fighting equipment. At construction sites, wooden planks and such items are often lying scattered, spillovers of oil and grease is common, gas cylinders are in use, electric wires run here and there to welding sets, machinery, illumination beacons. Chances of a fire break-out are often there. Fire extinguishers which must not be expired and must be functional should be available. Sand buckets should be kept ready. Fire fighting goggles should be kept for use whenever a fire breaks out. Some of workers should be trained to operate the fire fighting equipment. Water mist equipment should also be kept. Fire fighting hydrants should be created to draw water when required.
Some safety steps for handling of equipment: It will not be out of place if some important safety steps to be taken during handling of equipment are noted here—
1. All electric tools should be properly insulated.
2. All winches and hoists should be provided with magnetic brakes for automatic operation on failure of electricity.
3. No metallic ladders should be used when high voltage electric wires are passing overhead.
4. All compressed gas cylinders should be stored in upright position only, with their valve caps in position.
5. All equipment should be provided with proper earthing.
6. No electric tools should be used while standing in water without taking proper precautions.
7. Splicing of wire ropes should be avoided in critical areas.
8. Only skilled workers, well conversant with the plant and machinery should be allowed to handle it.
9. Proper railing should be provided around all working platforms at higher levels.
10. Any spill-over of oil or grease on ladders, stairs or landings should be cleaned at once.
11. The height of ladders should be restricted. Too long ladders should not be allowed and intermediate landing platforms should be provided to give relief to workers going up.
12. Proper bearing should be provided to the planks and battens used in temporary platforms. No overhangs should be permitted.
13. Full arrangements for storage and handling of explosives, radio-active elements and chemicals should be made, where necessary.