Confined Space Atmospheric Testing Procedure | Levels | Gas Limits

Confined Space Atmospheric Testing Procedure | Levels | Gas Limits

1. Monitors are used in the work area to ensure that safe atmospheric conditions are maintained and to check for pockets where leakage may cause isolated sections of hazardous atmosphere to accumulate.
2. Entry personnel must be evacuated immediately if there is ANY alarm. The reason for the alarm must be investigated and the Entry Supervisor notified immediately. No one enters the confined space until the situation is resolved.
3. Atmospheric monitors must only be operated by personnel that have been trained in the proper operation and limitations of the instruments.
4. Atmosphere monitoring equipment must have a current calibration and be function-checked before use, after use, and periodically during the work in accordance with manufacturer’s instructions.

5. Constant Monitoring

   • Constant O2 monitoring is required during permit required confined space entry operations if the initial oxygen content reading is outside the range 20.5–21.1%.
   • During confined space welding operations, constant atmosphere monitoring must be conducted for O2 and LEL. Consideration should also be given to constant monitoring for CO and other toxics based on the ventilation provided.
   • Constant monitors provide continuous monitoring of confined space atmosphere and the readout is located outside of the space within view of the Attendant. Where long tubing runs exist and may delay readout of atmospheric changes, the entry plan may require supplementing constant monitoring with personal monitors. See paragraph 5.7.7.
   • Constant monitors for O2 content must have audible alarms warning at 19.5% and 23.5% oxygen or at national limits. In high noise areas, the Attendant must pay close attention to the monitor alarm lighting.
   • Constant LEL monitoring is required during permit required confined space entry operations if the LEL level cannot be lowered to below 1% LEL prior to or during entry.
   • Constant monitors for flammable atmospheres must have audible alarms set at 10% of the lower explosive limit (LEL) of the combustible gas for which it is calibrated.
   • Toxic monitors equipped w/ audible alarms must have alarm settings set at the appropriate PEL or TLV.

6. Independent Verification

   • Additional atmosphere monitoring equipment may be used periodically during entry to verify the operation of constant monitors. Additional equipment may include another constant monitor or a manually operated instrument (either passive sensor or manually operated, hand pump instrument).

7. Personal Monitors

   • Personal monitors are designed to be carried on the Entrants while in the confined space.
   • Personal monitors may be used to supplement constant and manually operated instruments, as necessary. Personal monitors are not to be used as a substitute to constant monitors.
   • Where the entry requires a long sample run on the constant monitoring equipment for the Attendant to monitor the atmospheric conditions, the entry planning may include the requirement to supplement the Attendant’s constant monitoring with personal monitors. This will allow the Entrants to also monitor the entry conditions and react to changing atmospheric conditions without notification from the Attendant.

8. Atmospheric Testing Process

   1. Testing must be conducted by competent person to detect potential atmospheric hazards as follows (or where National Limits specify, a tighter limit):
   2. Test all confined spaces to ensure that the following atmospheric conditions are met prior to entry and periodically during entry. Carry out these tests in the order indicated using a calibrated direct-reading instrument.
   3. Oxygen contents must not be below 19.5% or above 23.5% by volume. If an adequate oxygen level is not present, no other testing should be done until this oxygen level is established. No entry is permitted into confined spaces containing greater than 23.5% oxygen.
   4. Note:  A constant monitor is required during entry operations if the initial oxygen content reading is outside the range 20.5–21.1%. Flammable gas, vapor, or mist must be below 10% of the lower explosive limit. No entry is permitted into confined spaces containing greater than 10% LEL.
   5. Note:  Anytime the LEL level cannot be lowered to below 1% LEL prior to or during entry:
      • constant LEL monitoring is required during permit required confined space entry operations; and anytime the Attendant notes an increase in the LEL reading of 2% above the baseline reading during the entry, the space must be evacuated and the cause of the deviation investigated.
      • Atmospheric concentration of any toxic substance must be below 25% of its permissible exposure limit (PEL) or a threshold limit value (TLV). Entry into spaces with greater than 25% of the PEL or TLV are permitted with appropriate control measures implemented (i.e., respiratory protection, ventilation, and monitoring).
      • While not required to be read by a direct-reading instrument, make a visual observation for entries involving combustible dust. Do not enter confined spaces that contain combustible dust that obscures vision at a distance of five feet or less. (Note that some test instruments for flammable gases, vapors, and combustible dust do not work properly without sufficient oxygen present.)
      • If the atmospheric conditions identified above are not met (other than those specifically prohibited), then a specific entry plan shall be developed and personnel training conducted on the extraordinary entry conditions and other requirements (refer to 25-010542 and 25-011310).
      • The limitations of the monitoring instruments must be verified to see if there may be any interference from other gases or chemicals. Vendor manuals must be referenced.
      • Specialized monitors may be required to detect certain toxic gases. The EH&S Department must be contacted for more information if there is any uncertainty regarding these monitors.

9. Initial Atmospheric Testing

   • Entrants must be given the opportunity to witness atmospheric testing of the space.
   • Ventilate the space (if atmosphere is known to be hazardous).
   • Turn ventilation off and allow adequate time for the space to stabilize.
   • The length of ventilation shutoff time should vary due to size and shape of the space.
   • Perform initial testing of the space (off-spec results may require constant monitoring regardless of ventilation protocol).
   • Re-ventilate the space as necessary
   • If you want to enter without continuous ventilation (you must have eliminated the hazard):
     • Turn ventilation off, allow the space to stabilize and re-test.
   • If you want to enter with continuous ventilation (you are controlling the hazard):
     • Establish ventilation and allow adequate time for the space to stabilize
     • Test space with ventilation on
     • Ventilation must remain on during the entire entry process

10. Unacceptable Initial Atmospheric Test Results

    • Additional action must be taken if initial test results are not acceptable. These may include:
      • Performance of additional cleaning or isolation.
      • Use of forced air ventilation to control atmospheric hazards.
      • Performance of atmospheric testing must be repeated until acceptable results are obtained.

11. Retesting of Atmospheric Content in Permitted Confined Spaces

    1. Where there are known or potential atmospheric hazards, re-testing of atmospheric content must be done by competent person periodically during the entry as follows:
       • Prior to re-entry after a break period. This applies only if all persons (including the Attendant) leave the entry location.
       • Prior to re-entry after shift change.
       • Prior to re-entry after an event that may have changed conditions in the space.
       • Periodically, as required on the permit. Generally, 30 or 60 minute frequencies are good practice, however the frequency may be extended or increased based on the hazards and entry conditions. In all cases, atmosphere checks must be made following breaks in the work. Frequency of retesting is dependent on the following criteria:
       • The nature of space.
       • The results of initial testing. (For initial tests with no evidence of flammable gases or vapor, retesting frequency is typically low.)
       • The scope of work to be done.
    2. Retesting may be done with the ventilation on (if continuous ventilation is required by the permit).
    3. Retesting results must be recorded on the Confined Space Entry Condition Log.