Introduction
Lead acid batteries are used across all sorts of critical systems—telecoms, data centres, UPS rooms, transport networks—because they provide reliable backup power. But as with anything involving power and chemistry, they come with risks. When these batteries charge, they produce hydrogen gas, and if that builds up in a room, it can be a serious fire and explosion hazard. That’s why DSEAR applies—and why a risk assessment isn’t just a tick-box exercise, it’s a legal and practical necessity.
There’s a big misconception out there that any battery room needs full ATEX zoning, ventilation systems running 24/7, and explosion-proof everything. It’s just not true. If you understand how these systems actually behave—how much gas is produced and under what conditions—you can often design smarter solutions that still keep everyone safe.
That’s exactly what we did here. We used recombination technology to manage hydrogen levels in a way that removed the need for unnecessary zoning, heavy equipment costs, and all the disruption that comes with it. This wasn’t about cutting corners—it was about being accurate, proportionate, and safe.
Understanding Hydrogen Evolution and Recombination
Hydrogen is mainly generated during battery charging, especially if they’re overcharged. Flooded lead acid batteries (vented) just let that hydrogen out through a small flame arrester. VRLA batteries, on the other hand, are much better contained—they recombine hydrogen and oxygen internally and keep most of the gas inside, converting it back into water.
When set up properly, VRLA batteries emit very little hydrogen at all. That’s why they’re often installed directly into places like telecom rooms and data centres. But even then, you have to get your charging voltages right and know how the system behaves under fault conditions.
Flooded batteries without recombination? Different story. They emit hydrogen continuously during normal charging and require more aggressive ventilation to prevent hazardous accumulation. While BS EN IEC 62485‑2:2018 provides the overarching UK safety framework for stationary battery installations, industry guidance and design best practice typically recommend maintaining hydrogen concentrations below 1% by volume—well below the 4% lower explosive limit—to ensure a safe margin. So if you’re using flooded cells, precise ventilation calculations are a must.
Hazardous Area Classification
Hydrogen becomes explosive at just 4% concentration in air. We’ve all seen the case studies of battery rooms going up because this wasn’t managed properly. That’s why this step matters.
In many cases, it’s possible to show that only the inside of the battery cabinets themselves present a risk—Zone 2 of negligible extent. That’s a very small hazard area, and it can be controlled. You don’t always need to zone the whole room. But to do that, you need to prove it.
Recombination Technology Explained
Recombination vents and plugs are clever little devices. They let hydrogen and oxygen recombine into water and drop back into the battery, cutting down on gas emissions and saving you from constantly topping up water levels.
With the right recombination technology installed, guidance like IEC 62485-2 and IEEE/ASHRAE allows for a 50% reduction in ventilation requirements. In many cases, they make a big enough difference to avoid ATEX-rated ventilation altogether.
Our Approach
We were called in by the largest transport organisation in Wales. This wasn’t just any backup battery setup—it was part of a major comms and UPS project to keep operations running 24/7 across the rail network. If the batteries failed, it wasn’t just a power problem—it meant key communication systems went offline. So it had to be right.
The original design was old-school: flooded lead acid batteries, mechanical ventilation, ATEX-rated fans, and a huge price tag. We reviewed the entire setup and proposed a better approach:
- Battery type and gas calculations: We modelled hydrogen generation using IEEE and ASHRAE methods. The result? VRLA batteries with the right float voltage produced a tiny amount of gas. Flooded cells fitted with recombination vents reduced hydrogen by over 90%.
- Hazardous area classification: With recombination tech and natural ventilation in place, hydrogen never reached 1% in the room. That meant we could classify only the inside of the battery cabinets as Zone 2 of negligible extent. No need for room-wide zoning. We backed this up with real data—nothing speculative.
- Ventilation and detection: We ditched the always-on mechanical ventilation and replaced it with a simple hydrogen detector. If anything unusual happens, it kicks in the fans and shuts down the chargers. Otherwise, the room runs safely with natural airflow.
- Operational controls: We trained the team to spot signs of overcharging and made sure charging profiles stayed within spec. We also added telemetry to track voltage and temperatures in real time.
- Documentation and compliance: Our report went in with all the calculations, drawings, and recommendations. The enforcing authority reviewed and accepted it—no objections, no rework.
Industries That Benefit from This
We’ve applied this exact thinking in multiple sectors:
- Telecoms and data centres – no need for over-engineered ventilation if you’re using VRLA batteries.
- UPS systems for hospitals, control centres, and infrastructure – safer, cheaper, smarter compliance.
- EV and forklift charging rooms – flooded cells with recombination vents keep hydrogen manageable.
- Off-grid renewables and battery farms – keep it lean, safe, and effective.
Wherever backup batteries are installed, there’s a temptation to assume worst-case. But our job is to assess it properly and give you clear answers—so you don’t waste money or create risk by accident.
What the Client Gained
In this case, the client saved around 40% of their planned capital costs by removing the need for ATEX-rated infrastructure. They also reduced ongoing energy costs by eliminating the need for 24/7 mechanical ventilation. Maintenance dropped too—recombination vents cut down on water top-ups and fault checks.
More importantly, they got peace of mind. They knew that the system was compliant, safe, and resilient. And they now had a repeatable method for future sites—because this isn’t the last one.
Final Thoughts
Hydrogen hazards can’t be ignored—but they don’t need to be feared, either. If you understand how the systems work and use the right tech, you can control the risks without breaking the bank.
That’s where we come in. We don’t just quote the regulations. We interpret them, apply them properly, and help you build something safe that’s built to last.
And if you’re in a sector like transport, energy, or healthcare—where failure simply isn’t an option—you need partners who get that. Who know what’s at stake. Who care as much about the outcome as you do.