Safety Awareness - February 2021
03-02-2021
To ensure the safety of both personnel and exploration facilities, following the statutory requirements is mandatory. The potential explosion hazard posed by gases and vapours is clearly defined together with the required protection measures in a number of national and international standards.
Explosive Atmosphere
To ensure the safety of both personnel and exploration facilities, following the statutory requirements is mandatory. The potential explosion hazard posed by gases and vapours is clearly defined together with the required protection measures in a number of national and international standards. Explosion-hazardous areas are classified into classes and zones and specific protective measures are identified which must be undertaken.
Hazardous areas can be found in areas where free flowing gas can be expected from the well, or released from the mud returns coming from the well. In addition to this, the areas that store flammable liquids or gases should also be classified as hazardous areas, e.g. Paint store, battery rooms, acethylene bottle storage, fuel tanks and helicopter refueling stations (offshore). Note: As no dust considerations (Class II) are known for drilling or workover operations, these have been omitted for clarity.
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CLASS I - Gases |
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ZONE 0 |
Flammable atmosphere continuously present, or present for long periods (more than 1,000 hours per year) |
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ZONE 1 |
Flammable atmosphere likely to occur in normal operation (more than 10 hours per year, but less than 1,000 hours per year) |
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ZONE 2 |
Flammable atmosphere not likely to occur and if it occurs will exist only for a short time (less than 10 hours per year) |
When flammable gases or vapours are combined with oxygen in a specific ratio, they become explosive. Below the lower explosive limit (LEL) the mixture is too lean to burn and above the upper explosive limit (UEL) the mixture is too rich to burn. During drilling or workover operations, the explosive gases most commonly encountered are:
|
GAS |
AUTO-IGNITION TEMPERATURE* |
EXPLOSIVE RANGE* |
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Methane (CH4) |
537 - 580⁰ C |
5.0% to 15.0% by volume (v/v) |
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Hydrogen sulphide (H2S) |
232 - 270⁰ C |
4.3% to 46% by volume (v/v) |
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Ethane (C2H6) - rare |
472 - 515⁰ C |
3.0% to 12.4% by volume (v/v) |
*Note: Please check with local country specific requirements as values and ranges may differ.
The auto-ignition temperature is the minimum temperature required to ignite a gas or vapor in air without a spark or flame being present. Regardless of which system your organisation may be following, i.e. IEC Ex, ATEX or NEC500, the same considerations are followed.
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AREA CLASSIFICATIONS |
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Division 1: Where ignitable concentrations can exist all of the time or some of the time under normal operating conditions. |
Zone 0: Where ignitable concentrations exist all of the time or for long periods of time under normal operating conditions. |
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Zone 1: Where ignitable concentrations exist some of the time under normal operating conditions. |
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Division 2: Where ignitable concentrations are not likely to exist under normal operating conditions. |
Zone 2: Where ignitable concentrations are not likely to exist under normal operating conditions. |
Review your hazardous area equipment at least annually, including the detection, protection, monitoring, controlling and measurement items. Also verify that like is replaced with like or increased protection items.
Remember that some regulatory bodies will only accept specific system types.
