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Author: Veress Árpád · Explosion-protection expertDAILY Ex - 15 SEPTEMBER 2026
ExTAG interpretations may look distant from the plant floor, but they eventually reach equipment selection, inspection and acceptance. The Imperial Sugar case shows what happens further down the chain: accumulated dust, an overheated bearing, and secondary explosions that turned a local ignition into a plant-wide disaster. The use case closes the loop with a spray booth whose measured airflow is dropping. Recalculating the remaining margin against the actual application rate identifies the intervention threshold, which a calendar-based filter change would miss. An Ex-safe condition has to be kept true, not filed once.
What changed + what happened + one Operational Ex decision
- What changed - today is ExTAG day in Beijing
The IECEx Technical Assessment Group (ExTAG) meets today, 15 September, during the IECEx Annual Meetings in Beijing. ExTAG is particularly relevant because it deals with the practical application and interpretation of Ex standards within the IECEx certification system; IECEx also maintains ExTAG Decision Sheets as an additional source on applying Ex standards.
There are already current technical subjects in the IECEx system around issues such as ignition risk from lithium cells/batteries, combined electrical/non-electrical equipment marking, and implementation of the new IEC 60079-0 edition.
Operational Ex comment: Technical interpretations matter when they eventually affect equipment selection, certification, inspection or acceptance.
For Operations, the chain should be: technical change → applicability check → affected assets → Ex Register/procedure → competence → verification
- What happened - Imperial Sugar: a small ignition became a plant-wide disaster
A useful older case today: Imperial Sugar, Georgia.
Sugar dust accumulated throughout the facility. The CSB concluded that dust inside an enclosed conveyor was likely ignited by an overheated bearing. The initial explosion disturbed accumulated sugar dust elsewhere, producing devastating secondary explosions.
14 people died and 36 were injured.
The important Operational Ex lesson is the barrier chain: dust generation → containment/extraction → housekeeping → equipment condition → ignition → secondary dust dispersion → escalation
Note: Once several barriers had degraded, one local ignition source was enough to create a catastrophic event.
Operational Ex comment: Housekeeping is not cosmetic. Where combustible dust layers can become a secondary explosion fuel, cleaning standards, inspection frequency and equipment maintenance are explosion-protection barriers.
- One Operational Ex use case - “Airflow is getting lower. Do we need to change the spray-booth filter?”
Yesterday we considered increasing spray-booth completely. Periodic ventilation measurement shows that the actual airflow is lower than before.
The measured airflow together with the actual material application rate to recalculate concentration and the remaining operating margin. This allows Head of Operations to identify the airflow level at which intervention/filter replacement becomes necessary rather than relying only on a calendar interval.
The question is: “Does the ventilation barrier still maintain the demonstrated safe condition?”
The decision chain becomes: measured airflow ↓ → available safety margin ↓ → intervention threshold reached → maintenance → airflow verification → return to service
If the required ventilation can no longer be demonstrated - reduce loading or STOP the operation.
That is why Ex cannot finish at commissioning. Define the barrier → inspect it → measure it → maintain it → recognize degradation → intervene → verify restoration.
An Ex-safe condition it is something Head of Operations has to keep true