Safety code for working in compressed air

IS 4138 - Scope Summary & Key Tables

Scope (Clause 2.0):
Defines terms and conditions for decompression procedures related to exposure periods and maximum working pressures.

Key Tables: Decompression Tables (Clause 2.1.2)

These tables specify decompression stages, pressure steps (in bar), and total decompression time (minutes) based on exposure duration and maximum working pressure.

Example: Decompression Table for Exposure > 2 to 3 hours

Notes:

• Stages: Pressure is reduced gradually in stages to avoid decompression sickness.
• Total Time: Sum of time spent at each pressure stage.
• Pressure Units: Bar (1 bar ≈ atmospheric pressure at sea level).

flowchart TD
    A[Exposure Period] --> B{Max Working Pressure}
    B -->|1.0-1.4 bar| C[Decompression Stages]
    B

IS 4138 - Definitions & Key Tables Summary

Clause 2.0: Definitions

• Specifies terms used in the standard for clarity.
• Example: "Maximum Working Pressure" - highest pressure allowed during operation.

Key Tables for Decompression (Clause 2.1.2)

Typical Table Format (Example from Table 2)

• Stage Pressures: Stepwise pressure reductions to avoid decompression sickness.
• Total Time: Sum of time at each stage.

Usage Notes:

• Follow decompression tables based on exposure duration and max pressure.
• Each pressure stage has a specified hold time.
• Critical for safe operations involving pressurized environments.

flowchart LR
    A[Max Working Pressure] --> B[Stage 1 Pressure]
    B --> C[Hold Time]
    C --> D[Stage 2 Pressure]
    D --> E[Hold Time]
    E --> F[...]
    F --> G[Surface Pressure (0.2 bar)]
    G --> H[Total Decompression Time]

Summary: IS 4138 defines decompression procedures with tables specifying pressure stages and hold times for safe pressure reduction after exposure. Use the tables according to exposure duration and max working pressure.

IS 4138: General Requirements for Structures - Key Points

IS 4138 primarily deals with pressure and time regulations for compression in structural elements. The key provisions are summarized below:

Key Clauses (B-1.1 to B-1.5):

• Pressure Regulation:
  Limits on allowable compressive stresses to ensure safety during construction and service.

• Time Regulation:
  Minimum durations for which compressive loads should be applied to avoid sudden failure.

Typical Pressure-Time Relationship (Conceptual):

General Specifications:

• Follow gradual application of compression to avoid shock loading.
• Use safety factors as per IS code guidelines.
• Monitor load duration to prevent creep or sudden failure.

Example Formula (Conceptual):

[ \sigma_{allow} = \frac{P}{A} \leq f_c \times \text{Time Factor} ]

Where:

• ( \sigma_{allow} ) = allowable compressive stress
• ( P ) = applied load
• ( A ) = cross-sectional area
• ( f_c ) = characteristic compressive strength
• Time Factor = reduction factor based on load duration

flowchart LR
    A[Start Compression] --> B{Load Duration?}
    B -->|Short| C[Lower Allowable Stress]
    B -->|Medium| D[Moderate Allowable Stress]
    B -->|Long| E[Highest Allowable Stress]
    C --> F[Apply Load Gradually]
    D --> F
    E --> F
    F --> G[Monitor Structural Safety]

For detailed tables and specific values, refer to Appendix B of IS 4138.

IS 4138 - Air-Lock Design and Construction: Key Points

1. Air-Lock Definition (Clause 2.1)

• A chamber facilitating passage between different air pressures (e.g., compartment to normal atmosphere).

2. Minimum Dimensions & Volume (Clause 4.3)

• Clear headroom: ≥ 1.8 m at center.
• Minimum air space per occupant: 0.85 m³.
• Must allow occupants to avoid cramped positions.
• Refer to Fig. 1 for detailed dimensions (typically length and width to accommodate personnel and materials).

3. Equipment Requirements (Clause 4.3)

• Pressure gauges: For man-lock attendant and occupants to monitor pressures inside lock and working chambers.
• Clocks: Visible to attendants and occupants.
• Communication: Bells, whistles, or telephones for non-verbal signals.
• Control: Ability for attendant to reduce/cut compressed air supply remotely.

4. Valves (Clause 4.4)

• Non-return valves or taps controlling air flow.
• Must ensure precise control to comply with pressure regulations (Clause 5.3).

5. Structural Design (Clause 16.2)

• Well steining and connections must withstand air pressure during pneumatic sinking.

Summary Table: Air-Lock Minimum Dimensions & Volume

Conceptual Mermaid Diagram of Air-Lock System

graph LR
  A[Working Chamber] -- Pressure --> B[Air-Lock]
  B -- Pressure --> C[Normal Atmosphere]
  B -- Pressure Gauges --> D[Man-lock Attendant]
  B -- Communication --> D
  D -- Control Valves --> B

This diagram shows the air pressure flow and control points in the air-lock system.

Note: For detailed dimensional drawings, refer to Fig. 1 of IS 4138:1977.

IS 4138: Duties of Lock Attendants & Compression/Decompression Rules

Key Duties of Lock Attendants (Clause 5.1 & 5.5)

• Control compression/decompression rates for personnel entering/leaving compressed air working chambers.
• Maintain a register recording:
  • Entry & exit times of each person in the man-lock.
  • Pressures in the working chamber at entry/exit.
  • Decompression times and other operational details.
• For persons exposed to pressure >1.25 kg/cm² within last 5 hours and entering a different lock, the attendant must obtain written particulars of last decompression (Clause 5.5).

Compression/Decompression Rules (Clause 1.25 & 5.1)

Register Format (Summary from Clause 1.25 Table)

Important Notes:

• Gradual decompression is critical to avoid decompression sickness.
• Lock attendants must be competent and vigilant.
• Escape routes and access (Clause 4.9) must be clear and safe.

flowchart TD
    A[Worker enters man-lock] --> B{Pressure >1.25 kg/cm²?}
    B -- Yes --> C[Lock Attendant controls compression]
    C --> D[Record entry time & pressure]
    D --> E[Worker enters working chamber]
    E --> F[Work period under pressure]
    F --> G[Worker exits working chamber]
    G --> H[Lock Attendant controls decompression]
   

IS 4138: Working Chamber Conditions - Key Points

1. Door Operation (Clause 6.1)

• Door between working chamber and man-lock to lower pressure must remain open when personnel are inside, except if impractical.

2. Temperature & Pressure Monitoring (Clause 1.25)

• Record details during shifts:
  • Compression pressure/time
  • Working chamber pressure
  • Decompression pressure/time
  • Wet bulb temperature in working chamber
• Maintain logs with times of entry/exit and pressure readings.

3. Decompression Tables (Clause 2.1.2)

• Decompression stages reduce pressure gradually to avoid decompression sickness.
• Exposure time over 1 h to 4 h affects decompression schedule.

Summary Diagram: Working Chamber Pressure & Decompression Flow

flowchart LR
    A[Entry to Lock] --> B[Compression Stage]
    B --> C[Working Chamber at Max Pressure]
    C --> D[Decompression Stage (Multiple Steps)]
    D --> E[Exit Lock to Normal Pressure]

Keep records as per IS 4138 for safety and compliance.
Use decompression tables strictly to ensure safe pressure transitions.

IS 4138: Temperature Control in Working Chamber

Key Specifications:

• Clause 7.1:

  • A wet bulb thermometer must be installed in every working chamber.
  • Mercury thermometers are prohibited; use alcohol or non-toxic alternatives.

• Clause 6.1:

  • Doors between the working chamber and man-locks to lower pressure must be kept open when not in use, unless impractical.

Temperature Monitoring Table (Excerpt from Clause 1.25):

Decompression Table (Clause 2.1.2):

(Refer to IS 4138 Table 7 for full details.)

Summary:

• Always monitor wet bulb temperature with approved thermometers.
• Maintain door protocols to ensure safety.
• Follow decompression schedules based on working pressure and exposure time to avoid decompression sickness.

flowchart LR
    A[Working Chamber] -->|Wet Bulb Temp Monitoring| B[Temperature Log]
    A -->|Pressure Monitoring| C[Pressure Log]
    B & C --> D[Compression/Decompression Schedule]
    D --> E[Safe Egress]

IS 4138: Pressure Control and Monitoring - Key Points

Pressure Regulation & Decompression Rates

• Decompression rate: Not faster than 0.4 bar/min (Clause 3.2, Note 1).
• Decompression applies both to the first stage and between stages.
• For borderline max working pressures, use the longer decompression procedure (Note 3).

Decompression Tables (Exposure Periods & Max Working Pressure)

(Refer to Tables 2, 3 & 4 for detailed stage pressures and times based on exposure period)

Important Notes

• Time between stages is not included in total decompression time (Note 2).
• Exposure period categories:
  • Over ½ h to 1 h (Table 2)
  • Over 1 h to 1½ h (Table 3)
  • Over 1½ h to 2 h (Table 4)

Summary Formula for Decompression Rate:

[ \text{Decompression Rate} \leq 0.4 , \text{bar/min} ]

flowchart TD
    A[Start at Max Working Pressure] --> B[Decompress to Stage 1 Pressure]
    B --> C[Hold for Stage Time]
    C --> D{More Stages?}
    D

IS 4138: Medical Supervision and Examination for Compressed Air Work

Key Clauses & Specifications

• Clause 10.2: Employers must arrange medical supervision and examinations by a qualified doctor at suitable locations.
• Clause 10.3 & Appendix D: Use Form No. 2 (Compressed Air Health Register) to record:
  • Date of examination
  • Employer & site address
  • Result & conditions affecting employment
  • Doctor’s signature

• Clause 9.1: Every compressed air worker must carry an ID badge indicating:
  • Compressed air worker status
  • Location of medical lock
  • Emergency protocol: taken to medical lock, not hospital/police

Additional Notes:

• The standard includes updated decompression tables for safer workmen decompression.
• Medical locks and air supply specifications are detailed for safety.

Summary Diagram: Medical Supervision Flow

flowchart TD
    A[Employment in Compressed Air Work] --> B[Medical Examination by Doctor]
    B --> C[Record in Compressed Air Health Register (Form No. 2)]
    C --> D[Issue ID Badge with Medical Lock Info]
    D --> E[Emergency Protocol: Take Worker to Medical Lock]

For detailed decompression tables and medical lock sizing, refer to the full IS 4138 standard.

IS 4138: Medical-Lock Key Specifications

• Clear Head Room: Minimum 1800 mm (1.8 m) at highest point (Clause 11.2).
• Compartments: Two compartments to allow entry under pressure (Clause 11.2).
• Doors: Each door must have:
  • Bull's eyes (viewports).
  • Air valves operable from inside and outside.
• Environmental Controls: Proper heating, lighting, and ventilation.
• Equipment inside lock:
  • Couch ≥ 2 m length.
  • Blanket, dry woollen garments.
  • Food lock.
  • Communication: Intercom/telephone and non-verbal signaling means.
  • Observation windows for outside monitoring (Clause 11.2).
• Air Supply:
  • Oil and CO-free air source.
  • Pressure increase capability: from 0 to 5.27 kg/cm² within 5 minutes (Clause 11.3).
• Personnel: Only certified gas testers using approved methanometers for gas detection (Clause 14.1).

Summary Table

flowchart LR
    A[Outside] -->|Door with bull's eye & air valve| B[Compartment 1]
    B -->|Air valve & door| C[Compartment 2]
    C -->|Door with bull's eye & air valve| D[Inside Medical Lock]
    B & C -->|Intercom/Signals| E[Communication System]
    B & C -->|Observation Windows| F[Outside Observers]

This ensures safe medical access under pressure with continuous monitoring and communication.

IS 4138: Safety Against Fire Hazard - Key Points

IS 4138 primarily deals with safety in compressed air work environments, including fire hazard precautions.

Key Specifications for Fire Safety:

• Man-lock Size: Adequate dimensions to ensure safe entry/exit.
• Medical-lock Air Source: Should be from uncontaminated, safe air supply.
• Decompression Tables: Use revised decompression schedules to prevent accidents.

Important Safety Measures:

• No alcohol consumption during compressed air work (Clause 12.2).
• Fire hazard precautions include proper ventilation, fire-resistant materials, and emergency protocols (implied by safety focus).

Fire Safety Formulas & Tables (General Guidance):

While IS 4138 does not provide explicit fire hazard formulas, general fire safety engineering principles apply:

• Fire Load (Q):
  [ Q = \sum (mass \times calorific value) ]
• Minimum Fire Resistance (R):
  Based on occupancy and material, typically from IS 1642 or IS 3023 for fire resistance ratings.

Summary Table (Typical Fire Safety Parameters):

Conceptual Flow of Fire Safety in Compressed Air Work

flowchart LR
    A[Work Environment] --> B[Fire Hazard Assessment]
    B --> C[Control Measures]
    C --> D[Safe Man-lock Design]
    C --> E[Safe Air Supply]
    C --> F[Emergency Procedures]
    F --> G[Use of Decompression Tables]
    G --> H[Worker Safety]

Note: For detailed fire resistance ratings, refer to IS 1642 and IS 3023. IS 4138 focuses on operational safety, including fire hazard awareness and preventive measures.

IS 4138 - Gas Detection and Monitoring Key Points

1. Gas Detection (Clause 14)

• Personnel: Only persons with gas-testing certificates from Chief Inspectorate of Mines are authorized.
• Equipment: Use approved methanometers for methane and hazardous gas detection.
• Lighting: Use only approved electric lamps, hand lamps, and torches (Clause 13.2).

2. Decompression Tables (Clauses 2.1.2, C-3)

• Used for safe decompression after exposure to high-pressure environments.
• Two tables based on exposure duration:

(Refer to IS 4138 Table 5 & 2 for detailed stage pressures and times.)

Summary:

• Use certified personnel and approved methanometers for gas detection.
• Follow decompression schedules strictly to avoid decompression sickness.
• Use approved lighting to prevent ignition in hazardous atmospheres.

flowchart TD
    A[Certified Personnel] --> B[Use Approved Methanometer]
    B --> C[Detect Methane/Hazardous Gas]
    C --> D[If Gas Detected]
    D --> E[Evacuate & Ventilate]
    F[Decompression] --> G[Follow Stage Pressures & Times]
    G --> H[Safe Return to Surface]

For detailed decompression times and pressures, consult IS 4138 Tables 2 & 5.

IS 4138 - Prohibition of Alcohol Consumption

Key Specification (Clause 12.2)

• No person employed shall consume alcohol while working in compressed air.
• No person under the influence of alcohol shall be permitted to enter the compressed air work environment.

Safety Context (Relevant to Compressed Air Work)

• Alcohol affects judgment and physiological response, increasing risk of decompression sickness.
• Strict prohibition ensures worker safety during exposure to high-pressure environments.

Related Decompression Tables (Clauses 2.1.2 & C-3)

• Tables specify maximum working pressures (in bar) and decompression stages with total decompression times.
• Example from Table 2 (Exposure 1 h to 1 h):

• Longer exposure tables (3-4 h, >4 h) increase decompression time accordingly.

Summary

• Alcohol consumption strictly forbidden in compressed air work (IS 4138, Clause 12.2).
• Follow decompression schedules meticulously to avoid health hazards.
• Ensure workers are sober before entering compressed air environments.

flowchart TD
    A[Worker enters compressed air environment] --> B{Under influence of alcohol?}
    B -- Yes --> C[Entry denied]
    B -- No --> D[Allowed to work]
    D --> E[Follow decompression schedule]
    E --> F[Safe decompression and exit]

Always prioritize safety by enforcing alcohol prohibition and decompression protocols.

IS 4138: Emergency Procedures and Communication – Key Points

1. Decompression Charts (Clause 3.2)

• Charts showing compression and decompression times must be displayed prominently at each air-lock entrance.
• These charts guide safe decompression to prevent decompression sickness.

2. Decompression Procedure (Clause 2.1.1)

• Determine each person’s basic pressure and working period.
• Use Tables I to 8 for decompression schedules based on these parameters.
• For multiple persons in a man-lock, use the highest working pressure and longest exposure time for the decompression schedule.

3. Exemptions (Clause 1.2)

• Decompression procedures do not apply if exposure pressure ≤ 1.25 kg/cm² during the working period.

Typical Decompression Table Format (simplified):

(Refer IS 4138 Tables I to 8 for detailed schedules)

Summary Diagram of Procedure:

flowchart TD
    A[Start: Determine Basic Pressure & Exposure Time]
    B{Is Pressure > 1.25 kg/cm²?}
    C[Use Decompression Tables (I to 8)]
    D[No Decompression Required]
    E[Follow Decompression Schedule]
    F[Display Charts at Air-lock Entrance]

    A --> B
    B -- Yes --> C --> E --> F
    B -- No --> D --> F

Ensure clear communication and visible charts to maintain safety during emergency decompression.

IS 4138 Decompression Tables Summary

These tables specify decompression schedules for exposure periods in high-pressure environments, ensuring safe pressure reduction to avoid decompression sickness.

Key Notes (Clause 3.2)

• Decompression rate: Not faster than 0.4 bar/min between stages.
• Total time: Excludes intervals between stages.
• For borderline max working pressure, use the longer decompression procedure.

Decompression Tables Overview

Example: For exposure >4h, max pressure 1.8-2.0 bar

Usage Tips

• Select table based on exposure duration.
• Use stage pressures to decrement pressure gradually.
• Follow total decompression time strictly.

Visual Concept: Pressure Reduction Stages

graph LR
A[Max Working Pressure] --> B[Stage 1 Pressure]
B --> C[Stage 2 Pressure]
C --> D[Stage 3 Pressure]
D --> E[Final Pressure (Atmospheric)]