A diesel generator is an ignition-capable machine, so near a process unit the question shifts from “how many kW” to “where can it legally and safely sit.” OSHA’s 1910.307 standard for hazardous (classified) locations requires electrical equipment in a classified area to be approved for that class, division or zone. A standard rental generator is generally not built to that approval. In practice, that means the generator is placed outside the classified boundary and power is run in through cabling and distribution. The plant’s own area classification drawings and safety team decide where that boundary falls, so confirm it with them before the unit is ordered.
This page covers the power side of that decision for turnaround planners. For scheduling and shutdown-window planning, see our guide to turnaround power plans.
Why turnarounds make the boundary harder
During normal operation, the classified boundary around a unit is well understood and rarely changes. A turnaround breaks that stability. Vessels are opened, lines are blanked or purged, and crews, lifts and scaffolding crowd areas that are usually kept clear. The boundary that applied to a running unit may not apply to the same spot mid-shutdown, and the reverse can also be true.
That is why generator placement is a permit and safety-office decision first and a logistics decision second. A location that looks convenient on a site map may sit inside an area the safety team wants treated as classified, or on a route that will carry heavy equipment later in the schedule. Settling this early avoids moving a running generator after cables are already pulled.
What stays outside, and what goes inside
The common pattern is simple: the engine-driven equipment stays outside the classified area, and only what the area permits goes in. The table below shows how that split usually works. Treat it as a planning aid, since the plant’s own classification and permit rules always govern.
| Item | Typical placement | Planning note |
|---|---|---|
| Diesel generator | Outside the classified boundary | Needs clear access for refueling and service |
| Fuel storage | Outside the classified boundary, per site rules | Plan refueling windows around other shutdown work |
| Distribution and transfer equipment | Outside, unless approved for the area | See power distribution options |
| Cable runs | Cross the boundary to the load | Route away from lift paths and vehicle traffic |
| Loads inside the area | Equipment approved for that location | Confirmed by the plant, not the rental yard |
Questions to settle before you request a quote
Most delays on this kind of job come from answers that did not exist yet when the unit was ordered. The list below is the information that lets a rental team size and stage equipment without a second round of calls. Gathering it takes one conversation with the safety office and the electrical lead. Our page on the decisions a turnaround power plan should settle before shutdown sets these out by planning stage and owner.
- Where the nearest generator-eligible location sits relative to the classified boundary, and who approves it
- The total load, and whether the loads are continuous or cycle on and off
- How far the cable run must travel, and the voltage the loads need
- Whether the work needs a transfer switch or can run on generator power alone
- How often fuel can be delivered, and whether a larger tank would reduce visits
- Whether the schedule has a second phase that moves loads to a new area
Cable distance changes the plan
Because the generator sits back from the unit, the run to the load gets longer. Longer runs mean more attention to voltage drop, cable handling and routing. A generator that is correctly sized on paper can still underperform at the far end of a long run if the cabling was not planned with it. Use the power calculator for the load side, then talk through the run with the rental team.
Fuel is the other consequence of distance. A generator placed away from the unit is also away from the easiest refueling path, and shutdown traffic can make a late delivery harder. Extended-runtime options such as a rental fuel tank can reduce how often a truck needs to reach the unit. Whether that is worth it depends on your site’s access rules and shutdown schedule.
Redundancy for a shutdown that cannot slip
When one outage window holds the whole schedule, a single failure on a critical load can cost more than the rental itself. Some planners run two units, or a primary with a standby, for those loads. Paralleling generators is another option when the load is larger than one unit but needs to scale as phases open and close. Whether redundancy is warranted is a judgment about the cost of a stoppage, so weigh it against your window rather than defaulting to it. For how a single failure carries through to the finish date, see how one temporary power failure can extend a turnaround.
How Stag supports turnaround power in Houston and the Gulf Coast
Stag Power Rentals supplies diesel generators from our Dickinson, TX yard to industrial sites across the region, and our team can talk through placement, cabling and fuel planning with your planner before anything ships. Bring the area classification drawing and the load list to that call, and we can tell you what we would stage and what we would need the plant to confirm. For the broader picture of how we support builds and shutdowns, see our construction and industrial power overview. When you are ready to scope a job, you can request a quote.
Frequently Asked Questions
Can a rental diesel generator go inside a classified area?
Generally no. OSHA 1910.307 requires electrical equipment in a classified location to be approved for that class, division or zone, and standard rental generators are not typically built to that approval. The usual approach is to site the generator outside the boundary and run power in. Your safety office has the final say on what is allowed where.
Who decides where the generator can be placed?
The plant does. The safety office and electrical lead use the area classification drawings and the turnaround permits to approve a location. A rental provider can advise on clearances, access and cabling, but cannot declare an area non-classified.
Does the classified boundary change during a turnaround?
It can. Opening vessels, purging lines and shifting work zones may change how the plant treats an area compared with normal operation. Confirm the boundary for each phase rather than assuming the one from the running unit still applies.
How far does the generator need to be from the process unit?
There is no single answer, because it depends on the plant’s classification, permits and site rules. Ask the safety office for the nearest eligible location, then plan cable length and voltage drop from that point.
How do I reduce refueling trips near a unit?
A larger fuel tank can lengthen run time between deliveries, and scheduling refueling outside peak shutdown traffic can help. Which combination works depends on your site’s access rules and how long each phase runs.
What information should I send with a quote request?
Send the total load, voltage, expected run duration, cable distance, fuel plan and any phase changes in the schedule. If you have the area classification drawing, bring it to the first call. That lets the rental team size and stage equipment without a second round of questions.