Summary
- The Environment Agency is consulting on Iron Mountain application EPR/LP3020MX/A001 for a regulated combustion installation at Dundee Road, Slough.
- The application covers plant at or above the 50MW rated thermal input threshold and requires assessment of emissions, operating techniques, and energy efficiency.
- Publication of the application does not establish generator count, fuel type, electrical output, operating hours, or eventual permit approval.
Iron Mountain has applied for a bespoke environmental permit covering large-scale combustion equipment at its Dundee Road data centre site in Slough.
The Environment Agency published application EPR/LP3020MX/A001 on 13 August under Section 1.1 Part A(1)(a) of the Environmental Permitting Regulations. That regime covers fuel combustion where an appliance, or qualifying combination of appliances, reaches an aggregate rated thermal input of at least 50MW.
The public notice does not specify how many generators are involved, what fuel they would use, their aggregate electrical output, or how many hours they are expected to run. The 50MW figure refers to thermal energy entering the combustion equipment rather than the IT capacity of the data centre or the electrical output of the generator fleet.
Standby power sits inside two regulatory systems
Large data centres are designed around electrical redundancy, with backup power available when normal grid supply is interrupted. At the scale now common in major clusters, the machinery required to provide that resilience can itself become a regulated industrial installation.
Environmental permitting examines different questions from data centre planning. The Environment Agency considers emissions, fuel and raw-material use, operating techniques, site condition, monitoring, waste, energy efficiency, and the application of best available techniques. Planning authorities are more likely to focus on the building, land use, traffic, visual impact, noise, and the broader acceptability of development.
Running hours are particularly important in understanding the environmental profile. Emergency generators are intended for rare loss-of-grid events, but they may also operate during testing, maintenance, commissioning, and other circumstances allowed under a permit. A fleet can therefore have substantial installed capacity while recording relatively limited annual fuel consumption.
The opposite can also occur during an extended power failure, when several machines may run together for much longer than their routine testing schedule. Permit conditions establish the environmental boundaries within which that resilience system can be exercised.
Without the detailed supporting documents, it would be premature to infer engine technology or pollutant levels at Dundee Road. Nitrogen oxides, particulates, stack design, dispersion, and local air quality all depend on the final plant, fuel, exhaust treatment, loading, and permitted operation.
Slough packs more infrastructure into an established cluster
Slough remains one of the UK’s densest data centre markets, built around proximity to London, extensive fibre connectivity, and a long-established ecosystem of operators and engineering suppliers. That maturity also places facilities inside a crowded network of power, roads, buildings, and environmental constraints.
Backup fleets grow with critical load. A large facility may need enough generator capacity to carry its essential electrical systems while retaining redundancy for maintenance or failure, which means installed standby capacity can exceed the load expected during a normal outage scenario.
Batteries already play a substantial role in bridging short power interruptions and allowing generators time to start, and longer-duration energy storage is improving. Replacing combustion plant for multi-hour or multi-day resilience is harder because the amount of stored energy required increases quickly with facility load.
Operators are also examining lower-carbon fuels, fuel cells, and alternative forms of on-site generation, although each brings its own supply, storage, cost, and reliability constraints. A backup technology that performs well in annual emissions calculations still has to remain available during the low-frequency event for which it exists.
Environmental permitting therefore exposes a less visible side of data centre expansion. Headline development announcements tend to focus on IT megawatts, construction investment, or customer demand; permit applications show the scale of the supporting plant required to keep those megawatts online.
The Environment Agency consultation remains open until 11 September.
No conclusion can yet be drawn on whether a permit will be granted or what operating conditions would be attached. A determination and the underlying technical documentation will provide a clearer view of the equipment, emissions controls, and operational envelope intended for the Dundee Road site.
