Introduction
Floating Production Storage and Offloading (FPSO) vessels play a crucial role in offshore oil and gas production. Given their exposure to hydrocarbons, understanding hazardous area classification is essential for safety, equipment selection, and regulatory compliance. This article explores how FPSOs are classified into different hazard zones and provides insights into designing safe offshore facilities.
What is Hazardous Area Classification?
Hazardous area classification is a method used to identify areas at risk of explosive atmospheres due to the presence of flammable gases or vapors. It helps determine the type of electrical and instrumentation equipment suitable for each zone, ensuring safe operations in offshore environments.
Hazardous Area Zones on an FPSO
The classification of hazardous areas on an FPSO follows international standards such as:
- IEC 60079-10-1 (International Standard for Gas and Vapor Hazardous Areas)
- API RP 500 / 505 (Recommended Practices for Electrical Installations in Petroleum Facilities)
Hazardous areas are divided into three main zones based on the likelihood and duration of flammable atmospheres.
Zone 0 (Continuous Presence of Gas)
- Definition: An area where an explosive gas atmosphere is present continuously or for long periods.
- Examples on FPSO:
- Inside cargo tanks and slop tanks (hydrocarbon vapors are always present).
- Inside vent masts (gas discharge points).
- Equipment Requirement: Must be intrinsically safe (Ex ia) to prevent ignition.
Zone 1 (Frequent Presence of Gas)
- Definition: An area where an explosive atmosphere is likely to occur during normal operations.
- Examples on FPSO:
- Pump rooms and process modules (handling crude oil and gas).
- Turret and mooring systems (hydrocarbon transfer from subsea wells).
- Surrounding cargo tank vents and relief valves.
- Equipment Requirement: Explosion-proof (Ex d) or intrinsically safe (Ex ib).
Zone 2 (Occasional Presence of Gas)
- Definition: An area where an explosive atmosphere is not likely in normal operations but may exist for a short time due to leaks or malfunctions.
- Examples on FPSO:
- Areas adjacent to Zone 1, such as around process areas and tank vent exits.
- Surroundings of relief valves, deck drains, and gas detection points.
- Equipment Requirement: Non-sparking (Ex nA, Ex nC, or Ex ic) or encapsulated (Ex m).
Non-Hazardous Areas
- Definition: Areas where hydrocarbons are not expected under normal conditions.
- Examples on FPSO:
- Living quarters and control rooms (kept pressurized to prevent gas ingress).
- Electrical switchgear rooms (located in safe zones).
- Equipment Requirement: Standard industrial electrical and instrumentation systems.
Hazardous Area Layout of an FPSO
A hazardous area layout visually represents the distribution of Zone 0, Zone 1, and Zone 2 areas across an FPSO.
Key Features in the Layout:
- Zone 0 (Red Areas) – Inside cargo tanks, slop tanks, and vent masts.
- Zone 1 (Orange Areas) – Process modules, pump rooms, turret, and areas around vents.
- Zone 2 (Yellow Areas) – Adjacent to Zone 1, including around relief valves and vents.
- Non-Hazardous (Gray Areas) – Living quarters, control rooms, and helideck.
Equipment Design for Hazardous Areas
The selection of electrical and instrumentation equipment depends on the zone classification.
| Hazardous Zone | Equipment Type | Protection Method |
|---|
| Zone 0 | Sensors inside tanks | Intrinsic safety (Ex ia) |
| Zone 1 | Process transmitters, control valves | Explosion-proof (Ex d) or Intrinsically safe (Ex ib) |
| Zone 2 | Junction boxes, analyzers | Non-sparking (Ex nA, Ex ic) or Encapsulated (Ex m) |
| Non-Hazardous | Control room equipment | Standard industrial-grade |
Why Intrinsic Safety is Preferred in FPSOs
Intrinsic safety (IS) is widely used in FPSOs for instrumentation and control systems because:
Safe Maintenance – Devices can be serviced without shutting down power.
Reduced Explosion Risk – Operates at low energy levels, preventing spark ignition.
Lighter Weight – Requires lighter cables and enclosures, reducing offshore weight.
However, explosion-proof (Ex d) enclosures are still used for:
- High-power applications (motors, heaters).
- Equipment exposed to extreme vibration.
Conclusion
Understanding hazardous area classification on an FPSO is critical for safety, regulatory compliance, and proper equipment selection. By following the Zone 0, Zone 1, and Zone 2 classifications, FPSO operators can ensure a safe working environment while optimizing maintenance and operational efficiency.
