The one article where approach boundaries stop applying.
Electrolytic cell areas are the exception the rest of the standard is written around. Contact with exposed energized surfaces is normal operation here, not a failure — so 350 replaces the approach-boundary model with a defined cell line working zone and a different set of controls inside it.
350.1 applies to the electrical safety-related work practices used in the types of electrolytic cell areas. The requirements supplement or modify 110.2, 110.4, 130.1 and 130.9 for employees exposed to electrical hazards in the cell line working zone. Informational Notes point to Informative Annex L, NEC Article 668, and IEEE 463.
§ The cell line working zone
350.5(A) states the premise plainly: operation and maintenance of electrolytic cell lines might require contact by employees with exposed energized surfaces such as buses, electrolytic cells and their attachments. That is not a hazard to be eliminated — it is the job.
Approach distances. The approach distances used elsewhere in the standard are replaced. The zone is defined instead between exposed energized surfaces and grounded equipment, other grounded objects, or the earth itself — which may include temporarily insulating or guarding parts so the employee can work on exposed energized parts.
Zone boundaries. The article requires a method of determining the cell line working zone area boundaries.
Qualified persons shall be permitted to work within the cell line working zone.
Unqualified persons shall be trained to identify the electrical hazards they could be exposed to and the proper methods of avoiding them. When an unqualified person needs to enter the zone for a specific task, they shall be advised of the electrical hazards by the designated qualified person in charge to ensure they are safeguarded.
§ Arc flash inside the zone
350.5(D) requires that each task performed in the cell line working zone be analyzed for the likelihood of arc flash injury. Where injury is likely, one or more measures must be taken:
- Providing PPE to prevent injury from the arc flash hazard.
- Altering work procedures to reduce the likelihood of an arc flash incident.
- Scheduling the task so it can be performed when the cell line is de-energized.
An arc flash risk assessment shall be done for all routine tasks in the cell line work zone, and the results used in training employees in job procedures that minimize the possibility of arc flash hazards. That training folds into the 350.3 requirements.
Before a nonroutine task is performed in the zone, an arc flash risk assessment shall be done. Where an arc flash hazard is possible, instructions shall be given to the employees involved on how to minimize the risk.
The routine/nonroutine split is the structural idea worth borrowing even if you never touch a cell line. Routine tasks get their assessment baked into training once; nonroutine tasks get an assessment before the task. Most electrical safety programs have the first half and improvise the second.
§ Does this apply to you?
For most data centers, no. Article 350 governs electrolytic cell areas — chlor-alkali, aluminum reduction, electrowinning, industrial electroplating lines. A conventional critical facility has none of these.
It is worth knowing the article exists for two reasons. First, the renumbering: this was Article 310 in the prior edition, and Article 310 now means something entirely different — dc electrical hazards. A procedure citing "Article 310" for cell work is now pointing at a dc threshold article.
Second, if your campus adds hydrogen electrolysis for fuel-cell backup or on-site generation, you have acquired an electrolytic cell area and this article comes with it.