By Eamonn Ryan
Behind the simple idea of ‘less oxygen, no fire’ sits a complex but mature piece of engineering.
© Cold Link Africa
Hypoxic fire prevention systems work by generating nitrogen on site and feeding it into the protected space to dilute oxygen down to the required level. During his talk, Andrew Brink of Gas At Site walked the audience through what this looks like in a real cold‑chain facility.
He described a typical example: a 70 000m³ cold store requiring around 30kW of compression to power the nitrogen generator. These units use air separation technology to take in ambient air (about 78% nitrogen, 21% oxygen) and produce a stream of enriched nitrogen.
“If we want to… bring [oxygen] from 21% down to 15% we’ve got to disperse it with something, and we disperse it with nitrogen… we generate the nitrogen on site and then we inject that nitrogen into the protected space,” said Brink.
Once injected, this nitrogen mixes through the warehouse, gradually pushing down oxygen concentration. The system then monitors and maintains the target level around 15% – not just once, but continuously, 24/7.
A major factor in sizing and running these systems is leakage. No warehouse or cold store is perfectly sealed, and operational reality demands doors, hatches and penetrations. Brink was candid: “Clearly, the building that you’re going to protect, in an ideal situation, you don’t want any leaking apertures… but that’s obviously not practical.”
The more air leaks in or out, the more nitrogen must be generated to maintain the setpoint: “The more holes you have in the building, the more nitrogen you have to generate in order to maintain [the setpoint].” – Andrew Brink
Design choices therefore matter a great deal:
- Door types and duty cycles (for example, five‑minute doors, rapid‑roll doors)
- Use of airlocks between ambient and low‑oxygen zones
- Air curtains or strip curtains to reduce mixing at openings
- Operational rules around how long doors may stand open
These factors directly affect electricity consumption and operating cost. Brink summed up the trade‑off in practical terms: “If I’m running FMCG, and I’m in and out all the time, I’m throwing some money off the bed, but if I’m storing documents, or I’ve got a cold store that I pack and I leave like that, it’s a wonderful investment.”
To ensure safe, stable conditions, the system uses optical oxygen sensors with triple redundancy, aligned with relevant EN and ISO standards:
“The technology that measures the oxygen is optical and highly reliable. It’s got triple redundancy to make sure that people can breathe sufficiently if they’re in these areas… It’s not low oxygen by guesswork, it’s controlled to accurate sequence and maintained.” – Andrew Brink
In Part 5, we zoom out again to consider occupational health, system limits, insurance acceptance, and how this technology shapes the future vision of the cold store.