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Author: Veress Árpád · Explosion-protection expertDAILY Ex - 18 SEPTEMBER 2026
An unplanned outage takes a refinery offline, maintenance works the problem, power comes back, and the phones start ringing about restart. But power restored is not the same as Ex-safe condition restored. During an abnormal shutdown, ventilation can disappear, gas detection can lose availability, interlocks can be overridden for troubleshooting and temporary equipment arrives on site. The use case examines one of those: a portable fan brought in when permanent ventilation is unavailable, in an area whose classification assumed that ventilation. The closing exercise: find one temporary arrangement in your hazardous area and check whether it is still covered.
Production people know this situation very well. The plant in shutdown. Phones start ringing. Maintenance works on the problem. Power returns.
The question to here: “When can we restart?”
See real world Ex.ample:
A power outage on 13 September took ExxonMobil’s Joliet refinery in Illinois offline. According to the company, power was lost at around 15:30 and restored around 19:00. The outage triggered the refinery’s safety flare and a plant-wide shutdown. Units then had to be assessed and stabilised.
On 17 September, another operational issue was reported at Joliet: floodwater had affected a pump and containment measures were deployed. There is currently no basis for saying this was connected to the earlier electrical outage.
This isn’t presented as an Ex incident.
Meaning:
Power restored does not mean Ex-safe condition restored.
Note: During an abnormal shutdown, quite a lot can change.
Ventilation can disappear. Gas detection may lose availability. Pumps stop. Pressure conditions can change. Inerting can be affected. Equipment can remain partially isolated.
Maintenance teams enter the plant. Temporary cables, lighting, pumps or ventilation may be introduced. Interlocks may be overridden for troubleshooting.
And somebody eventually has to decide that the plant is ready to operate again.
That somebody has to be the Head of Operations.
Before restart, the Head of Operations doesn’t personally need to inspect every Ex gland or understand every protection concept. Head of Operations needs confidence that the conditions supporting explosion safety have been restored.
HAC assumptions • ventilation • gas detection • inerting • Ex equipment • inspection findings • temporary equipment • overrides • isolations • PTWs • open maintenance • MoC • temporary deviations
The key here:
“Can we demonstrate that the plant we are about to restart is inside its documented Ex-safe condition?”
🌎Operational Ex use case of the day - temporary ventilation
Imagine a maintenance shutdown in a process building. Permanent mechanical ventilation is unavailable. The job needs to continue, so somebody brings in a portable fan. From a productivity perspective, problem solved.
From an Operational Ex perspective, several new questions just appeared.
If ventilation was an assumption behind the hazardous-area classification, then changing the ventilation arrangement may affect the HAC basis itself.
Where does the temporary fan take its air from? Where does it discharge? Is the fan suitable for its location? Can it become an ignition source? What happens if it stops? Is failure detected? Does loss of ventilation require shutdown? Has the temporary arrangement been assessed through MoC or a controlled temporary deviation?
And
Who has the authority to say NO if those answers cannot be demonstrated?
That is the connection between Ex engineering and the Head of Operations.
Engineering defines the safe condition. Inspection and maintenance help preserve it. Documentation records it. Operations decides whether the plant continues to operate within it.
Today’s Operational Ex question:
Walk through your plant and identify one temporary arrangement in a hazardous area.
A fan. A pump. A cable. Temporary lighting. A bypass. An overridden alarm. A temporary repair.
Is this still covered by our demonstrated Ex-safe condition - or has “temporary” quietly become normal operation?