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IS 4138:1977 is the Indian Standard (BIS) for safety code for working in compressed air. This standard lays down the safety requirements for workers employed in compressed air environments, such as during the construction of caissons, shafts, and tunnels. It provides detailed protocols for medical fitness, safe compression and decompression rates, working hour limits based on pressure, and mandatory emergency medical facilities to prevent decompression sickness.
Safety code for working in compressed air
Overview
Status
Current
Usage level
Specialized
Domain
Geotechnical — Construction Management incl. Safety
L96 (ACOP)Health and Safety Executive (HSE), United Kingdom
HighCurrent
Work in compressed air. The Work in Compressed Air Regulations 1996. Approved Code of Practice and guidance.
Directly covers safety procedures, medical requirements, and decompression for work in compressed air.
29 CFR 1926 Subpart SOccupational Safety and Health Administration (OSHA), USA
HighCurrent
Underground Construction, Caissons, Cofferdams, and Compressed Air
Provides mandatory federal regulations for compressed air work in construction, including tunneling and caissons.
Code of Practice: Tunnelling workSafe Work Australia, Australia
MediumCurrent
Code of Practice: Tunnelling work
A broader tunnelling code that includes a specific and detailed section on compressed air work.
ITA Report No. 003International Tunnelling and Underground Space Association (ITA-AITES)
MediumCurrent
Guidelines for Good Occupational Health and Safety Practice in Tunnel Construction
Provides international industry guidelines for tunnel safety, with a significant chapter dedicated to compressed air working.
Key Differences
≠IS 4138:1977 is significantly outdated and based on 1970s medical and engineering knowledge, whereas modern standards like HSE L96 are based on recent hyperbaric medicine research and a risk-assessment-based approach.
≠The Indian standard specifies air-only decompression tables. Modern standards (e.g., HSE L96) provide tables and guidance for using oxygen during decompression, which significantly reduces decompression time and the risk of decompression sickness.
≠International standards like OSHA and HSE place a strong emphasis on formal safety management systems, risk assessments, and specific documented roles (e.g., dive supervisor, medical advisor), which are not explicitly detailed in the more prescriptive IS 4138.
≠Air quality requirements are much stricter in modern standards. For example, the limit for Carbon Monoxide in OSHA regulations is 5 times lower than in the IS code.
Key Similarities
≈All standards mandate the fundamental principle of staged decompression to allow for the safe off-gassing of dissolved nitrogen from a worker's body to prevent decompression sickness (the 'bends').
≈The requirement for pre-employment and periodic medical examinations by a qualified physician to ensure workers are fit for the hyperbaric environment is a core safety tenet in all listed standards.
≈All codes require the use of man locks for personnel and the presence of a competent lock attendant at all times during compression and decompression operations.
≈The need for an on-site medical lock for the recompression treatment of decompression sickness is a common requirement, especially for work exceeding a certain pressure threshold.
Parameter Comparison
Parameter
IS Value
International
Source
Maximum Recommended Working Pressure
Work above 3.5 kg/cm² (approx. 3.4 bar) should be avoided.
Work at a pressure exceeding 3.5 bar requires specific justification and notification to the HSE.
HSE L96
Carbon Monoxide (CO) Limit in Breathing Air
Shall not exceed 50 parts per million (ppm).
Shall not exceed 10 ppm.
OSHA 29 CFR 1926.803(k)
Medical Lock Requirement Threshold
Required for work at pressures above 1 kg/cm² (approx. 1 bar).
Required for all work unless a risk assessment justifies its absence (and HSE grants an exemption). The default is to have one.
HSE L96
Minimum Age for Workers
No person under 18 years of age.
No person under 18 years of age.
HSE L96
Decanting Prohibition
Not explicitly forbidden; rapid decompression is noted as a cause of decompression sickness.
'Decanting' (rapid decompression with transfer to a separate chamber) is explicitly forbidden.
HSE L96
Communication
A telephone or other signal device shall be provided between the lock and the working chamber.
Two independent communication systems are required between the working chamber, the man lock, and the surface.
ITA Guidelines
⚠ Verify details from original standards before use
Key Values6
Quick Reference Values
minimum age of worker20 years
maximum age of worker50 years
minimum fresh air supply0.3 m3/min per person
max compression rate0.35 kg/cm2 per minute
pressure requiring medical lock> 1.0 kg/cm2
maximum working pressure3.5 kg/cm2 (without special permission)
Tables & Referenced Sections
Key Tables
Table 1 - Working Shifts and Intervals at Various Pressures
Table 2 - Decompression Rates and Timings
Key Clauses
Clause 4 - Medical Examination and Fitness of Workers
Clause 5 - Man-Locks and Working Chambers
Clause 6 - Compression Procedures
Clause 7 - Decompression Procedures
Clause 8 - Working Hours and Rest Intervals
Clause 10 - Medical Lock Requirements
Frequently Asked Questions3
What is the age limit for workers in compressed air?+
Workers must be between 20 and 50 years of age.
When is a medical lock required on a construction site?+
A medical lock is mandatory when the working pressure in the chamber exceeds 1.0 kg/cm2.
What is the minimum fresh air supply required per worker?+
A minimum of 0.3 cubic meters of fresh air per minute must be supplied per person in the working chamber.