Better safe than sorry - Guest Article -Er. Jagvir Goyal
It augurs well for construction companies to lay down strict safety measures in construction of tall RCC Chimneys to avoid unnecessary accidents and delays.
Construction of tall RCC Chimneys has always been a high risk operation involving continuous working during the use of slip forms. Another feature of chimney construction is working at high elevations, that too under working-space constraints. Often, bad weather conditions are also faced during chimney construction and there is no escape from that.
Under such conditions, there are always greater chances of occurrence of accidents than those during normal construction activity. In multi-flue chimneys, the situation becomes more complicated during the construction of internal platforms where the work is taken up at the same time on more than one front, one above the other. There is every chance of objects falling from upper working fronts to lower ones in case no safety precautions are taken.
Therefore, during the construction of tall RCC chimneys, safety aspects assume a special significance and can't be ignored. A systematic and effective safety program has to be compulsorily followed during the entire span of chimney construction.
Let us divide the safety measures to be taken up during chimney construction into the following four categories:
- Accident Prevention measures.
- Worker’s protection equipment.
- Equipment maintenance and other aspects.
- Existence of Safety cell
Let us elaborate on each of these categories:
Accident Prevention Measures
The following measures help in prevention of accidents during the construction of Chimney:
a) Restricted Shift hours: It is normal tendency with most of the construction companies to work in twelve hour shifts, thus in two shifts per day. A twelve hour shift though provides advantage of overtime, additional pay and bonus to the workers. Yet, from a safety point of view, it is not favourable. Workers posted at higher elevations are fatigued if they put in 12-hour shift leading to their not remaining alert. The number of shift hours should be restricted to eight only. Three shift working may require additional manpower, but such initiatives prevent accidents at site.
b) Deploy skilled workers only: Chimney construction being a specialized job, only such workers should be engaged to work who possess the experience of working on high elevations and who are adequately trained for the jobs to be performed by them. All of these workers should be medically fit to work at high altitudes.
c) Activity timing: The work schedule should be so framed that the best weather of the year is available for the slip forming activity. Preferably, slip forming work should be carried out in summers only. This will not only result in better progress but will minimize accidents because in summer days, more daylight working hours shall be available, concrete shall gain strength earlier and workers shall have better flexibility. Slip forming during winters or rainy season may cause serious problems at site. Workers may repeatedly fall ill or have lesser mobility.
d) Minimum work fronts: In multi-flue chimneys, the activity of construction of platforms takes a long time for completion. Chimneys are tall and the internal platforms are vertically spaced at about 10 metres interval. A number of platforms are, therefore, to be constructed one above the other to support the lining work. For fast completion of this activity, more than one work fronts need to be opened. Otherwise, the construction of platforms alone, leave apart the other activities, may claim more than a year. It has, therefore, become a practice to work at many fronts for earliest completion of internal platforms.
While the opening of more than just one front increases the progress manifolds, it makes the construction work a high risk operation also. The workers engaged on lower fronts are always exposed to the objects falling down from the upper level fronts.
In order to ensure safety of workers, the number of working fronts should be kept as minimum as possible for completion of platforms within the planned period. Moreover, under such circumstances, all the open voids in the platforms should be provided with false sheet-blanketing except the space through which the material buckets are to be passed. Workers on higher elevations should be better skilled, careful and instructed to take all precautions. Work on lower fronts should be suspended on days when there are greater chances of objects falling from upper levels, such as on concreting days.
e) Protection against fire: Sufficient and effective fire-fighting equipment should be available on all work fronts to take care of any fire that erupts during working. Some of the workers should be trained to operate the fire fighting equipment.
f) Protection against bad weather: Special arrangements should be made to fight bad weather. Workers, staff and engineers posted at high elevations shall not be able to get down to ground level when the work is suddenly struck by high velocity winds, gales, heavy rains or storms, etc. Rain coats should be provided on the working decks. A temporary shelter made of GI sheets should be erected on the top deck. Sufficient anchorage should be provided to the working decks so that high velocity winds don't cause their uplifting. These measures should be fully observed during slip form operations when the top deck, working deck and mason’s deck are more susceptible to high velocity winds.
g) Safe access arrangements: In a chimney, proper and safe access arrangements are to be made to reach higher levels and working decks. Modular staging towers should be erected to encase the ladders, which should be strong, stable and broad-based. These must be adequately braced and secured. A number of instances have been noted where the staging towers have buckled when a height of more than 90.00 m has been achieved. An investigation into such accidents has revealed that the main reasons for such happenings have been inadequate base width, provision of lesser number of bracings or worker's tendency to remove a clamp or bolt from the lower parts of the tower for use at higher levels.
An effective way to brace the staging tower is to provide anchorage hooks at regular height intervals in the chimney shell during its construction and later, to tie the tower to these anchorage hooks.
h) Safe passenger hoist: The passenger hoist provided for carrying workers to various work fronts should be made fully safe. The capacity of the winch for the passenger cage should be kept in view while deciding the maximum number of workers that can ride the passenger cage. Only double drum, double rope hoist should be used for passenger cage. The access platform, or cage, should be provided with an upper limit switch, an emergency stop button and a cushioned base for shockproof landing on the ground.
i) Safety mesh: A nylon mesh should be provided all around, covering the outer hanging scaffold, the working deck and the top deck during slip forming work. The nylon mesh shall protect the workers and prevent the goods slipped down from the decks from falling. A similar mesh should be provided on the inner face of decks as well.
j) Warning signs: The area around the chimney should be cordoned off at ground level and no person should be allowed to enter it without wearing safety helmet or without permission. Accident prone areas on the ground level should have red indication lamps during night and the warning signs during day displaying 'Danger', 'Men working overhead', 'Beware of falling objects' etc.
Workers’ protection equipment
Workers engaged on chimney construction should be provided with proper safety equipment to avoid any injury. The worker protection equipment is explained below:
a) Safety helmets: No worker should be allowed to enter the chimney area unless he/she is wearing a safety helmet, irrespective of his/her working level i.e. ground level or higher levels. Workers normally do not find it convenient to work with safety helmets on. They take off their helmets and put them aside once they are permitted entry to their work-fronts. Such a tendency should be curbed. Workers should be habituated of working with helmets on their heads. A regular check against non-wearing of helmets should be performed by the supervisors.
b) Safety belts: All the workers working in the unprotected areas or on the upper decks should wear safety belts which can save them from slipping down.
c) Gas masks: In thermal projects, a number of power production units are planned together. A unit is built, commissioned, starts producing power and work on the next unit is taken up. Often, there are chances that a chimney is in operation near the chimney under construction. Whenever there exist functioning chimneys near the chimney under construction, there is always a possibility of exposure to obnoxious gases.
Precautions should be taken to protect the workers from such attacks which may prove fatal, as the gases are poisonous. As an immediate precaution, workers should be provided with gas masks which they must wear as and when the gas blows in their direction. A watch over the direction of gas should be kept.
d) First Aid Boxes: During the construction of chimney, well-equipped First Aid Boxes should be provided on all working decks and workers should be educated about their use. Normally, first aid boxes are provided in the first instance, but are never upgraded or replaced after their use. Such a tendency should be avoided.
Equipment Maintenance and other Aspects
In addition to taking Accident Prevention Measures and providing Safety Equipment to workers, regular maintenance of equipment is very important to avoid its breakdown which may lead to accidents at site. Some of the commonly used equipment is discussed here:
a) Winches: Winches, or friction hoists, under use should be regularly maintained against any break downs, gear failures or such mechanical faults. All winches should be provided with auto-cut magnetic brakes which should act instantly in the event of power-failures.
b) Wire ropes: All wire ropes should be regularly lubricated, inspected and maintained. Splicing of wire ropes should not be allowed. There shouldn't be any kinks in the wire ropes. No loads should be allowed to rest on wire ropes. Any wear or tear in wire ropes, when noted, should be immediately repaired. Wire ropes should not be over-stretched. These should be replaced by new ones before subjected to prolonged use. All wire ropes should conform to IS specifications.
c) Lighting: All lighting fixtures should be kept in proper functioning condition. Sufficient illumination of all work fronts is essential. Emergency lights should be kept on all working decks to avoid panic among workers during power failures. Intermediate platforms, when being worked upon, become pitch dark during power failures and panic among workers is obvious. Diesel operated machinery and diesel generators should be provided at site and essential lighting equipment and fixtures should be connected to these for instant change over during power failures.
d) Lightning protection: Temporary lightning protection of Chimney must be ensured during its construction. It should be regularly checked against any disconnections and should remain functional until the time the permanent lighting protection arrangement has been made, tested and found functional.
e) Aviation warning lights: All chimneys, when they cross a height of 45 metres, should be provided with temporary aviation warning lights to guide the overhead planes about the existence of a structure below. The aviation warning lights are temporarily provided on the top most point of chimney. These should remain in working order during the entire construction period and until the time the permanent aviation warning lights have been installed on the chimney.
f) Earthing: Proper Earthing of all lighting fixtures, winches and other electrical equipment is vital for safety. Care should be taken that the Earthing arrangements have been made and remain intact. All electrically operated hand tools should be double earthed.
Existence of Safety Cell
A 'Safety Cell' should always be created at the site to ensure implementation of various safety measures during chimney construction. It is a general tendency among workers and engineers to ignore safety measures once the work has been started and is running smoothly. The accidents happen without prior warning and the importance of safety measures is then realized.
The 'Safety Cell' should keep a watch over the following items:
- No worker enters the work area without wearing safety helmet.
- No worker engaged in unprotected work zones is without safety belt.
- All the wire ropes are inspected daily and are lubricated at regular intervals.
- Regular maintenance of friction hoists is ensured.
- The Earthing arrangements are proper and maintained.
- The lightning protection arrangements and the aviation warning lights are in functioning order.
- All working platforms are well illuminated.
- Areas around the Chimney are well manned and cordoned.
- Access arrangements are proper and safe.
- The man-riding capacity of the passenger hoist is not exceeded.
- Protection arrangements against obnoxious gases have been maintained.
- A comprehensive insurance policy covers all the workers engaged on chimney work.
- No cutting or welding work is allowed without wearing of safety goggles and gloves by the workers.
- None of the workers travel up or down in concrete or material carrying buckets.
- Wire ropes and manila ropes, wherever used, are as per IS specifications.
- None of the workers touches the wire ropes in operation.
- All communication systems and signal systems are in perfect working order.
- Lifting capacity of all the lifting equipment is evaluated from time to time. It should be downgraded as per the condition or wear and tear of the equipment.
- Gas cylinders are kept in upright position wherever used. It is a normal practice to lay down the cylinders while using or storing them, which should be avoided.
- All timber planks used for working decks are checked to be sufficiently strong, free of splits, cracks or defects.
- Lessons on safety consciousness are given to the working staff and the workers by the safety cell from time to time.
- Prizes are distributed among safety conscious workers to set an example for others to adopt safety measures.
The safety cell should always comprise of competent and dynamic persons who take pride in saving workers and keeping the site accident free by frequent checks and steps in this direction.
Er Jagvir Goyal is an Author of technical books, and a feature writer for leading newspapers and journals of India.