An NGL processing plant on the Gulf Coast cut power-related safety-system downtime by 95 percent after replacing a single unprotected UPS with an N+1 redundant, ATEX- and IECEx-certified UPS built into purge-protected enclosures. The change protected its emergency shutdown and fire-and-gas systems against the voltage sags that had twice forced an unplanned process shutdown, and it has recorded zero safety-system power losses in the eighteen months since commissioning.
In oil and gas processing, the UPS does not sit quietly behind an IT rack. It feeds the emergency shutdown logic solvers, the fire-and-gas detectors, the distributed control system I/O and the telecommunication links that let an operator safely stop a plant. If that power blinks, the plant cannot be guaranteed to trip to a safe state, and the site is legally and physically exposed. A UPS in a classified area is therefore part of the safety instrumented system, and it has to meet the same rigour as the valves and transmitters it supports.
Process areas are divided by the likelihood that an explosive atmosphere is present. Zone 1 means an explosive gas-air mixture is expected to occur in normal operation; Zone 2 means it is only expected under fault conditions. Gas group matters too: group IIC covers hydrogen and most light hydrocarbons, which have the narrowest ignition-energy margin and demand the tightest equipment certification. A standard office UPS placed in or adjacent to such a zone is not merely non-compliant, it is a potential ignition source, because an internal arc or hot surface can reach the temperature needed to ignite the surrounding mixture.
Two certification families dominate. ATEX is the European framework and IECEx the international equivalent; both reference the same underlying test methods. Explosion protection is then achieved by one of several techniques. Flameproof construction, marked Ex d, contains an internal explosion within a heavy enclosure so hot gases are cooled below ignition temperature before they escape. Pressurization, marked Ex p, keeps the enclosure internal pressure above ambient so the explosive mixture cannot enter. For a UPS the practical choice is usually a pressurized enclosure housing the power electronics, with the battery in a separate non-classified room where it is easier and cheaper to maintain. Temperature class, written T1 through T6, caps the maximum surface temperature, and for light hydrocarbons a T4 rating, 135 degrees Celsius, is a common specification. The complete assembly is also sealed to at least IP66 against ingress of dust and water.
The plant fed its safety PLC and DCS I/O from a single line-interactive UPS mounted in a motor control centre room rated only for an unclassified space. During a compressor trip, a voltage sag on the incoming feeder dropped the DCS communication link for roughly ninety seconds. The control system could not confirm the safe state of its shutdown valves, so the operators initiated a full process shutdown as a precaution. Reaching a safe state, flushing the line and restarting took about fourteen hours, and the recurring pattern was costing the site on the order of two weeks of lost throughput per year across several such events.
The replacement used three online double-conversion modules in an N+1 configuration, each certified to Ex d and Ex p with a T4 temperature class and IP66 ingress protection. The battery strings were relocated to a separately ventilated, non-classified room so the largest and most heat-sensitive component was outside the hazardous envelope entirely. Output was wired through an isolated, grounded distribution scheme, and every module reported status, battery state of health and alarm conditions over the plant network to the central control room. Because the modules were online, the load never saw the utility directly, so the next compressor trip caused no disturbance at the safety PLC whatsoever.
In the first year after commissioning, power-related safety-system downtime fell from roughly fourteen hours to under forty minutes, a 95 percent reduction, and the avoided process shutdowns returned the project cost inside a single avoided event. The eighteen-month inspection found battery state of health at 98 percent, confirming the separated, climate-controlled battery room was delivering the expected service life. Just as important, the site moved from reacting to alarms after the fact to seeing battery and load trends before they became problems, which is the real value of certified monitoring on a safety-critical supply.
Our industrial and hazardous-area configurations are described at https://www.upsboss.com/industrial/, and the certified models behind them are listed at https://www.upsboss.com/products/.
Key takeaway: in a classified oil and gas area the UPS is a safety device, and certifying it to the zone, isolating the battery from the hazardous envelope and running it online with N+1 redundancy removes the single largest source of unplanned, power-driven process shutdowns.
Can a standard UPS be used inside a Zone 1 area?
No. A standard unit is a potential ignition source because of internal arcs and hot surfaces. It must carry the correct Ex certification for the zone and gas group, or be located in a separate non-classified room with properly rated conduits.
Why put the batteries outside the hazardous area?
Batteries are the largest, hottest and most maintenance-sensitive part of the system. Placing them in a ventilated non-classified room simplifies inspection, extends service life and shrinks the certified envelope to just the power electronics.
Does N+1 redundancy matter if the UPS is already certified?
Certification addresses ignition risk, not availability. A single certified module still fails, and on a safety load that failure must not stop protection, so N+1 is the right specification whenever the load drives a process shutdown.
Contact: Frank Zhang
Phone: +86-135 5688 8641
Email: frank@upsboss.com
Add: Jufeng Road, Guangming Street, Guangming District, Shenzhen City, Guangdong Province, China
