Quick answer
To protect biological samples in hot weather, control the ambient air temperature in the room, not just the freezers themselves. Keep ambient air at 25 °C or below, because ultra-low freezer compressors work much harder above that point. Back this with reliable freezer temperature monitoring and agreed alarm tolerances, a 24-hour on-call team that can reach samples within an hour, an uninterruptible power supply for outages, and a list of emergency suppliers for temporary air conditioning. For collections you cannot afford to lose, arrange a cold storage disaster recovery plan in advance.
Anyone responsible for a freezer room knows the feeling that arrives with the first heatwave warning. The forecast creeps up, a second hot spell is announced, and somewhere a -80 °C freezer uses more energy and takes a greater toll on its hardware. When the ambient temperature rises, especially above 25 °C, the machinery keeping samples frozen has to work harder to hold the freezer interior cold. As climate change makes extreme heat more frequent, that strain is becoming a normal part of the British summer.
UK Biocentre looks after more than 35 million biological samples across seven Azenta BioArc Flex automated stores, a new high-density BioArc Ultra automated store, and -196 °C liquid nitrogen tanks. As well as the higher-tech equipment, we also run 280 of the traditional -80 °C freezers that scientists would recognise from any university or research centre. We know where the real risks sit during hot weather and what keeps them in check.
Sam Willett, Director of Operations at UK Biocentre & SRS Europe, has spent years on exactly this problem. Protecting samples in summer depends far less on the freezers themselves than on the air in the room around them.
Why ambient air temperature counts more than the freezer in hot weather
When a heatwave arrives, the instinct is to study the freezer. Sam’s first piece of advice is to look past it, to the ambient air temperature in the room.
Cold storage units run on compressors, and compressors work much harder once the surrounding air rises above 25 °C. At UK Biocentre, anything above 25 °C triggers an alarm, and the team then brings that ambient temperature back down. They do this through air conditioning, and through discipline about how many units share a space. As Sam explains: “the compressors are dealing with hot air and pump out hot air, generally.” Crowd too many units into one area and each compressor fights the heat the others throw off.
The practical lesson for any laboratory or storage facility is to know the limits of your space. How many freezers can a given square footage support before the units begin competing for cool air? Sam keeps UK Biocentre’s ambient air at 25 °C or below, and treats anything above that as the point where conditions start to become dangerous.
UK Biocentre’s parent company Azenta’s guidance on safe storage temperatures for biological materials sets out the wider temperature ranges different sample types depend on.
What happens to ULT freezer compressors when they overheat
A ULT freezer compressor failure in hot weather is a real danger. A freezer forced to draw in warm air runs longer and longer cycles to hold -80 °C, and a compressor that never gets to rest has a higher breakdown risk. The freezers most at risk tend to be older and less energy efficient, sited in rooms with too little cooling and too many neighbours. Reducing the heat load on each unit is the most useful step you can take before the temperature climbs.
How to set up freezer temperature monitoring you can rely on
A freezer alarm that sounds at 3am helps no one if the first anyone hears of it is the following day. This is where Sam sees smaller biorepositories and university laboratories come unstuck. Too often the pattern is to switch the lights off at night and hope the freezer holds until morning.
Reliable freezer temperature monitoring reduces this risk significantly. At UK Biocentre, every freezer carries alarms and alarm tolerance levels agreed with the customer in advance. A -80 °C freezer, for instance, holds tolerances at -75 °C and -85 °C. Ambient air carries a tolerance around +27 °C. The limits are set, agreed and watched.
UK Biocentre worked with partner T-Scan to commission and install a system across all temperature monitoring, taking a reading every seven and a half minutes. It means the team, with its 24-hour presence, is never more than seven and a half minutes from knowing a freezer has begun to drift, which is the longest a unit could lose temperature before an alarm sounds.
Scientists and researchers should understand how each type of storage behaves in a heat failure. UK Biocentre’s quad banks lose roughly one degree an hour, which gives the team time and room to respond. A manual freezer behaves very differently, comfortably shedding 10, 15 or 20 degrees in an hour. Different equipment demands different reaction times, and a monitoring plan should reflect that, not treat every unit alike.
How quickly are samples at risk when a freezer fails?
Sample integrity is at risk from the first minute a unit drifts out of range. The wider industry often works to a window of several hours before frozen samples are compromised, but the safe assumption is that the clock starts immediately.
Response times are as important as the monitoring itself. UK Biocentre runs a 24-hour on-call team to a clear standard, with someone reaching the samples within the hour.
Sam recommends labs put a documented emergency plan in place for when a system fails. Include how systems are monitored, the escalation notifications to the lab management team, the suppliers who can be called upon and an emergency relocation plan. At UK Biocentre, disaster planning is carried out on a regular basis.
How to protect lab freezers during a power outage
Every manual freezer at UK Biocentre has its own power supply socket, and all of them connect to a central supply. Sam’s team has put in measures for power backup in the event that power is lost to the building compromising samples in the freezers and quad banks.
An uninterruptible power supply (UPS), paired with an automatic-mains-failure panel and a generator, keeps critical cold storage running while the building switches over. Alongside the hardware sit contingency documents written and ready, and a clear sequence of who does what if the power fails. A battery backup on a single freezer usually powers the alarm and electronics, not the compressor, so building-level resilience keeps samples frozen.
Sam’s view is that this is the other area, alongside monitoring, where smaller facilities tend to expose themselves. They tend to have older, less energy-efficient freezers that are more prone to failure, no on-call team and no secondary power supply. You can see how we build this resilience into sample storage solutions.
What to do when the temperature spikes and freezers start to struggle
Sam’s recommendation for research and academic institutions is to think about who they can call on if disaster happens and they need urgent help.
Keep a critical supplier list, made up of people who already understand they are on call for you. UK Biocentre does not employ its own plumbers, electricians or air conditioning engineers. Instead it holds a list of critical suppliers who know they are on a retainer and will come out in an emergency. If the air conditioning is failing during a spike, the supplier for temporary aircon can be on site within 24 hours, and an electrician within the hour.
Air conditioning can be costly to install, and if not needed all year round could pose an additional cost that would take years to show a return on investment. An alternative, a route that UK Biocentre has pursued, is to commission temporary air conditioning.
How far apart should lab freezers be placed?
A small detail catches people out: spacing. Pack freezers too densely and they trap heat around one another, making the compressors work harder to no purpose. Density is rarely a choice for labs holding their own collections; as space runs short, freezers tend to spill out of the laboratory and into the corridors. Dr Tony Cox, Chief Executive Officer at UK Biocentre, has described how -80 °C freezers end up lining corridors, “where we effectively have corridor biobanks, because they cannot occupy more space in the laboratories themselves.”
As well as the Azenta quad bank and BioArc Ultra technology onsite, UK Biocentre also has 280 traditional -80 °C freezers. The freezer spacing in their facility is 50 centimetres between each one (depending on the manufacturer’s instructions), giving a unit room to breathe. Fire regulations require one and a half metres between each row, so that people can move safely between them. UK Biocentre holds to both standards across all 280 freezers on site.
The cubic capacity of the room counts for less than you might expect. Sam has visited a customer in the USA running 1,900 freezers in a single room with no overheating problems, because their air conditioning more than meets the task. One freezer in a poorly cooled room can be too warm; a hundred in a well-cooled one can be fine. What governs the outcome is the ambient air, not the cubic space.
Why every facility needs a cold storage disaster recovery plan
Sam recommends all facilities have their own cold storage disaster recovery plan for if your own storage fails. UK Biocentre can assist laboratories experiencing a crisis, and have seen that organisations that come through a crisis tend to be the ones that decided, while everything was calm, where their samples would go if the worst happened. Our guide to preventing disasters in your sample storage walks through the steps in full.
Bringing it together
The facilities that come through a heatwave are the ones that understand the risks and build a plan for each: controlling the ambient air, monitoring you can trust, on-call responses, a secondary power supply, and a list of suppliers ready to move when the heat spikes. Smaller facilities tend to fall short if one or two of those links are missing.
UK Biocentre has spent years putting every link in place, across tens of millions of samples, through more than one heatwave. If your own summer planning has gaps in it, or you are not certain where the gaps are, that is exactly the kind of conversation our team is glad to have. You can explore our storage solutions, read more on preventing disasters in your sample storage, or simply get in touch.
Frequently asked questions
At what temperature do lab freezers start to struggle in hot weather?
Most cold storage units begin to labour once the ambient air around them rises above 25 °C, because their compressors have to work much harder to hold temperature. At UK Biocentre, anything above 25 °C triggers an alarm and prompts action to bring the room temperature back down.
How do you protect biological samples during a heatwave?
Control the ambient air temperature first, keeping it at 25 °C or below. Add reliable environmental and cold storage temperature monitoring with agreed alarm tolerances, a 24-hour on-call team that can reach samples before the temperature rises above agreed tolerances, an uninterruptible power supply for outages, and a list of emergency suppliers who can deliver at short notice.
What is the ideal ambient temperature for a room of -80 °C freezers?
Aim to keep ambient air at 25 °C or below. Above that, ultra-low freezer compressors run longer cycles and risk overheating. The room’s cubic size counts for less than the strength of its air conditioning relative to the heat the freezers produce.
How quickly are frozen samples at risk if a freezer fails?
Sample integrity starts to suffer from the first minute a unit drifts out of range, so the clock should be treated as starting immediately. UK Biocentre’s on-call team works to a standard of reaching affected samples within one hour of an alarm. An hour response is only possible because UK Biocentre’s quad banks and BioArc Ultra retain the cold so efficiently – a smaller organisation or lab may have freezers that heat more quickly and so the response time needs to be shorter.
How can I keep my freezers running during a power cut?
Building-level resilience keeps samples frozen: an uninterruptible power supply with an automatic-mains-failure panel and a generator to carry critical storage through an outage. A battery backup on a single freezer typically powers only the alarm and electronics, not the compressor.
How far apart should ultra-low temperature freezers be placed?
50 centimetres between each freezer so that each unit can breathe, with one and a half metres between rows to meet fire regulations and allow safe access.
What is a cold storage disaster recovery plan?
A cold storage disaster recovery plan sets out, in advance, who responds, time parameters, the escalation procedures, and where your samples will go if your own storage fails. These arrangements need to be set up early, before a crisis forces the question.
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