Safety code for tunnelling work
1978 Edition

According to IS 4756, tunnel ventilation must provide fresh, breathable air and eliminate harmful dust, explosives fumes, and toxic gases. The minimum airflow is 4.25 cubic meters per minute per worker plus 2.0 cubic meters per minute per brake horsepower of diesel engine power used underground. Air volumes should be increased in conditions of elevated temperatures or intensive blasting. Toxic gas concentrations must be kept below prescribed safety thresholds, ensuring a healthy environment for workers. The basic airflow calculation is Q = 4.25 × N + 2.0 × P, where Q is total ventilation in cubic meters per minute, N is the number of workers, and P is the diesel engine power in bhp. Continuous monitoring and adjustments are essential to maintain safe conditions.

IS 4756 mandates that explosives and detonators be transported separately in insulated containers to prevent accidental ignition. When moved by rope or locomotive haulage, separate compartments with a minimum 45 cm gap must be maintained, constructed from planks at least 5 cm thick, with doors opening on opposite sides and kept locked except during loading and unloading. The interior of transport vehicles must be free of exposed metal. An attendant must accompany explosives during underground transport, with prior approval from the Chief Inspector of Explosives. At work sites, explosives and detonators should remain secured in locked containers until use. If blasting holes are not yet ready, explosives must be stored in locked magazines at least 170 meters away from the area.

IS 4756 requires that all metallic structures such as steel forms and drill carriages be effectively grounded to prevent electrical hazards. Switches should be installed on elevated ground and also grounded. Temporary emergency lighting powered by batteries must be provided at working faces and at intervals to aid safe evacuation. Supervisors and team members should be equipped with cap lamps or hand torches, ensuring at least one lamp per ten workers. Given the wet and damp nature of tunnels, there is a heightened risk of short circuits; thus, electrical equipment must be robust, regularly inspected, and well-maintained. Additionally, all personnel should wear protective gear including helmets, steel-toe boots, gum boots, and safety belts where applicable.

For ensuring effective communication and alerting in tunnels, IS 4756 specifies the use of electrically operated bells powered by batteries or dry cells, with switches positioned outside the tunnel and movable according to tunneling progress. Alternatively, two magnet-type field telephones or other suitable systems like walkie-talkies may be employed. For tunnels up to 100 meters, one such system suffices; for longer tunnels, at least two systems should be installed, preferably with wiring on opposite sides. A telephone system is mandatory for tunnels longer than 500 meters or shafts deeper than 50 meters to facilitate quick communication. Battery-powered emergency lighting and personal lamps are also required to aid in safe evacuation.

IS 4756 requires that rolling stock such as carts used to transport pipes, rails, timber, or other materials be loaded so that the cargo remains within the side boundaries of the vehicle, preventing any protrusions that could pose hazards to personnel. For wide or oversized loads, special operational care and prominent warnings must be provided to workers along the track. Employees are prohibited from riding on unsafe areas such as locomotive front steps or couplings, with only authorized trainmen permitted on dump cars. The standard also emphasizes the need for protective equipment like helmets, steel-toe boots, and gum boots, and mandates safety belts in inclined or shaft areas to mitigate the risks associated with cramped space, poor lighting, slippery floors, and gas hazards.