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IS 4756:1978 is the Indian Standard (BIS) for safety code for tunnelling work. This standard outlines the essential safety practices and protocols for tunnelling work, including shaft sinking, excavation, drilling, and blasting. It details critical requirements for ventilation, illumination, fire protection, and the handling of hazardous gases to ensure the occupational health and safety of workers in underground environments.
Safety code for tunnelling work
Overview
Status
Current
Usage level
Specialized
Domain
Geotechnical — Construction Management incl. Safety
Guideline for Health and Safety in Tunnelling, 3rd Edition
Industry best-practice guidance on managing health and safety risks throughout the lifecycle of tunnelling projects.
Key Differences
≠IS 4756 is a prescriptive standard from 1978, while modern equivalents like BS 6164 are performance-based and centered on formal Safety Management Systems (SMS) and continuous risk assessment.
≠The Indian standard has very limited guidance on the use of modern Tunnel Boring Machines (TBMs) and associated automation, which are central to modern standards.
≠Modern standards have a significantly stronger focus on occupational health, including detailed requirements for managing long-term exposure to respirable crystalline silica (RCS), diesel particulate matter (DPM), noise, and vibration.
≠IS 4756 has a simplistic two-tier classification for 'gassy' tunnels, whereas modern standards use more detailed risk-based classifications for potentially explosive or toxic atmospheres, often linked to continuous electronic monitoring.
Key Similarities
≈All standards mandate the provision of adequate mechanical ventilation to control airborne contaminants (dust, gases) and ensure a breathable atmosphere.
≈Core principles of fire prevention are shared, including controlling ignition sources, managing flammable materials, and requiring firefighting equipment and emergency plans.
≈The fundamental requirement for at least two separate means of egress from the underground working area is a common principle for worker safety in emergencies.
≈All standards provide specific and strict safety protocols for the storage, handling, transport, and use of explosives for blasting operations.
Parameter Comparison
Parameter
IS Value
International
Source
Minimum Air Velocity (Ventilation)
9 m/min
0.3 m/s (18 m/min) is a common recommendation to prevent stratification
BS 6164:2019
Flammable Gas Action Level (Methane)
Suspend work at 0.5%; withdraw personnel at 1.25%
Action required at ≥10% of LEL (0.5% Methane); withdraw personnel at ≥20% of LEL (1.0% Methane)
OSHA 29 CFR 1926.800
Maximum Interval for Ladder Landings
9 m
50 feet (15.2 m) for fixed ladders in construction
OSHA 29 CFR 1926.1053
Minimum Oxygen Content
Not explicitly specified in percentage; air must be 'fit for breathing'
Must be maintained between 19.5% and 22.0%
OSHA 29 CFR 1926.800
Haulage Way Side Clearance
Minimum 60 cm on one side
Minimum 24 inches (61 cm) on one side for walkways
OSHA 29 CFR 1926.800
Emergency Lighting Level
System required, but no specific illumination level specified.
Minimum 1 lux at floor level along escape routes.
BS 6164:2019
⚠ Verify details from original standards before use
Key Values5
Quick Reference Values
Minimum oxygen content in tunnel atmosphere19.5% by volume
Maximum permissible concentration of Carbon Monoxide (CO)50 ppm
Maximum permissible concentration of Carbon Dioxide (CO2)0.5% by volume
Maximum permissible concentration of Nitrogen Dioxide (NO2)5 ppm
Maximum permissible concentration of Hydrogen Sulphide (H2S)10 ppm
What is the minimum oxygen level required inside the tunnel?+
The atmosphere must contain not less than 19.5 percent oxygen by volume.
How should blasting operations be safely conducted?+
Blasting must comply with IS 4081, ensuring workers are evacuated to safe distances and fumes are fully cleared before re-entry.
What are the rules for tunnel ventilation?+
Mechanical ventilation must continuously supply adequate fresh air to dilute noxious gases, blasting fumes, and dust below their respective threshold limit values.