Standard
Track updates
AS 4774.1:2026
[Current]Work in compressed air and hyperbaric facilities, Part 1: Work in tunnels, shafts and caissons
AS 4774.1:2026 specifies requirements to ensure safe working conditions for people entering and working under increased ambient pressure (excluding diving operations and hyperbaric treatment operations (refer to AS 4774.2), and to promote uniformity of practice in relation to the health and safety of persons working in or entering shafts, tunnels, tunnelling machines and compressed air caissons pressurized above atmospheric pressure
Published: 27/02/2026
Pages: 67
Table of contents
Cited references
Content history
Table of contents
Header
About this publication
Preface
1 Scope and general
1.1 Scope
1.2 Normative references
1.3 Terms and definitions
2 Personnel and duties
2.1 Duty of constructor
2.1.1 General
2.1.2 Requirements for medical fitness
2.1.3 Notification of authorities
2.2 Compressed air operations supervisor (CAOS)
2.3 Lock/shuttle/habitat operator
2.3.1 General
2.3.2 Instructions
2.3.3 Records
2.3.4 Control
2.4 Operators of other on-site hyperbaric chambers
2.5 Response personnel
2.5.1 Medical practitioner
3 Hazard identification, risk assessment and control
3.1 General
3.2 Hazard identification
3.3 Risk assessment
3.4 Risk control
4 Planning and procedures
4.1 Planning
4.2 Procedures
4.2.1 Operating procedures
4.2.2 Operational plan
4.2.3 Stability of working chamber
4.3 Training
4.3.1 Hyperbaric workers
4.3.2 Lock/shuttle/habitat operators
4.3.3 Worksite hyperbaric chamber operators
4.3.4 Compressed air operations supervisors
4.3.4.1 Routine operations pressurized to a maximum of 3.5 bar, with compressed air as breathing medium
4.4 Communications
4.5 Post-decompression identification
4.5.1 General
4.5.2 Hyperbaric worker identification
4.5.3 Access to pressure exposure data
4.6 Notices and instructions
4.7 Prohibition of smoking, alcohol or drug use
4.8 Maximum periods in compressed air
4.8.1 General
4.8.2 Mandatory rest period
4.9 Compression
4.9.1 Rate
4.9.2 Repetitive compression
4.10 Decompression
4.10.1 Decompression tables
4.10.2 Decompression procedures
4.10.3 Repeat decompression
4.10.4 Recompression protocol
4.11 Ventilation of the working chamber
4.11.1 Allowable limits of gaseous impurities
4.11.1.1 Chamber atmosphere
4.11.1.2 Supply air
4.11.2 Detection of gaseous impurities
4.11.2.1 General
4.11.2.2 Recording gaseous impurities
4.11.2.3 Sampling
4.11.2.4 Non-respirable atmosphere
4.11.3 Normal ventilation system
4.11.3.1 Supply air
4.11.3.2 Rate of air supply
4.11.3.3 Air circulation and exhaust
4.11.4 Special ventilation provisions for blasting
4.12 Change in pressure of the working chamber
4.12.1 Decompression
4.12.2 Unplanned change
4.13 Decanting
4.14 Safety rescue system
4.15 Control of oxygen
4.15.1 Oxygen supply
4.15.2 Oxygen piping
4.15.3 Oxygen system cleanliness
5 Medical requirements
5.1 Medical certification
5.2 Medical examination
5.3 Supervision of health
5.3.1 Advice to hyperbaric workers
5.3.2 Periodical medical examination
5.3.3 Prohibition of entry
5.3.4 Flying or diving after compressed air work
6 Plant
6.1 General
6.2 Personnel lock
6.2.1 General
6.2.2 Size
6.2.2.1 General
6.2.2.2 Tunnelling machine locks for use at less than 1 bar
6.2.3 Capacity
6.2.4 Seating
6.2.5 Doors
6.2.6 Access
6.2.7 Minimum equipment for personnel locks
6.2.7.1 Control panel
6.2.7.2 Instrumentation inside the lock and at the control panel
6.2.7.3 Instrumentation at the control panel
6.2.7.4 Lock operator equipment
6.2.7.5 Other equipment
6.2.8 BIBS oxygen decompression system
6.2.9 Ventilation
6.3 Worksite hyperbaric chamber
6.3.1 Requirements for a worksite hyperbaric chamber
6.3.2 General
6.3.3 Size
6.3.4 Instrumentation at the operator panel
6.3.5 Other requirements
6.4 Special provisions for working chambers
6.4.1 Communication
6.4.2 TBM working chamber
6.4.3 Pressurized tunnels
6.4.3.1 General
6.4.3.2 Overhead walkway
6.4.3.3 Safety curtains
6.4.3.3.1 General
6.4.3.3.2 Installation
6.4.3.3.3 Location of air supply
6.5 Special provisions for compressed air caissons and shafts
6.5.1 General
6.5.2 Number of locks
6.5.3 Location of personnel locks
6.5.4 Lock platforms
6.5.5 Personnel hoist
6.5.6 Height of working chamber
6.6 Compressed air supply
6.6.1 General
6.6.2 Supply air
6.6.3 Air tools
6.7 Compressed air plant
6.7.1 General
6.7.2 Air lines and fittings
6.7.3 Air exhaust
6.7.4 Monitoring
6.7.5 Testing of equipment
6.7.5.1 General
6.7.5.2 Pressure measuring devices
6.8 TBM breathing gas storage and pipework
6.8.1 TBM working chambers
6.8.2 Gas storage and handling systems
6.8.3 Supply pipework
6.8.4 Discharge pipework
6.9 Electrical installation
6.9.1 Wiring
6.9.2 Lighting
6.9.3 Lighting voltage
6.10 Fire control equipment
6.10.1 General
6.10.2 Pressurized tunnels
6.10.3 Tunnel-boring machines
6.10.3.1 Working chamber
6.10.3.2 TBM and backup
6.10.4 Welding or cutting
6.11 Personnel facilities
7 Special precautions — Use of explosives
7.1 General
7.2 Conforming to code
7.2.1 Explosives and detonators taken to the face
7.2.2 Tools and equipment
7.2.3 Persons in working chamber
7.3 Detonation — Before and after
7.3.1 Testing of pressure relief valves
7.3.2 Inspection of instruments
8 Records
8.1 Appointed medical practitioner’s (AMP) report
8.2 Additional records
8.2.1 Long-term records
8.2.2 Short-term records
8.2.3 End of employment
9 Hyperbaric worker responsibilities
9.1 General
9.2 Responsibilities
9.3 Hyperbaric worker’s logbook
10 Work at compression greater than 3.5 bar and saturation works
10.1 Planning and procedures
10.2 Respirable gases for work at > 3.5 bar
10.2.1 Gases
10.2.2 Operating procedures
10.2.3 Analysis of the gas working environment
10.2.3.1 Initial sampling
10.2.3.2 Continuous sampling
10.2.3.3 Gas scavenging
10.3 Training
10.3.1 Supervisory roles
10.3.1.1 Operational supervisor
10.3.1.2 AMP (or medical practitioner approved by the AMP)
10.3.1.3 Compressed air operations supervisor (CAOS)
10.3.2 Hyperbaric workers - mixed gas (HW-MG)
10.3.3 Saturation hyperbaric workers (SHW)
10.3.4 Lock, shuttle and habitat operators
10.3.5 Medics and rescue personnel
10.3.6 External support personal
10.4 General requirements for breathing apparatus
10.4.1 Communications
10.4.2 Equipment
10.4.2.1 Breathing apparatus
10.4.2.2 Helmets and masks
10.4.2.3 Hoses
10.4.2.4 Couplings and fittings
10.4.2.5 Inlet and exhaust valves
10.4.2.6 Demand gas supply
10.4.2.7 Cylinders
10.4.2.8 Bailout systems
10.5 Compression and decompression
10.5.1 Planning
10.5.2 Gas changing
10.5.3 Repetitive compression (no-saturation)
10.6 Saturation work
10.7 Saturation infrastructure
10.7.1 General
10.7.2 Habitat
10.7.3 Habitat building
10.7.4 Shuttle
10.7.5 Transfer vehicle
10.7.6 Locks
Appendix A
A.1 Introduction
A.2 General
A.3 Training in underwater and hyperbaric medicine
A.4 Fitness criteria
A.4.1 General
A.4.2 Conditional and restricted certifications
A.4.3 Age
A.4.4 Obesity
A.4.5 Skin
A.4.6 Vision
A.4.7 Ear, nose and throat
A.4.8 Hearing
A.4.9 Teeth
A.4.10 Central nervous system
A.4.11 Cardiovascular system
A.4.12 Respiratory system
A.4.13 Musculoskeletal function
A.4.14 Other criteria
A.4.15 Screening for dysbaric osteonecrosis (long bone X-rays)
Appendix B
B.1 Decompression illness — A brief introduction
B.2 Suggested instructions for persons in compressed air environments
Appendix C
C.1 Development
C.2 Protocol
Appendix D
Bibliography
Cited references in this standard
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Fixed platforms, walkways, stairways and ladders - Design, construction and installation
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