Many cold storage systems are described as "redundant." That can mean a second refrigeration system, a backup power source, extra alarms, or a combination of these. Each one protects against a different kind of failure.
This post explains what each type of backup covers and where gaps can remain.
What is a single point of failure in cold storage?
A single point of failure is any part that, if it stops working, causes the whole system to stop keeping product cold. Examples include the refrigeration unit, its controls, and the power supply. It’s important to note, the people who respond to alarms are part of the system as well.
What does a backup refrigeration system do?
A backup refrigeration system takes over if the main system fails. It keeps product cold while the main system is repaired. Backup refrigeration is usually planned when a system is first designed, because it's harder to add later.
WHO guidance for pharmaceutical cold rooms and freezer rooms says each room should have full standby capacity in case a refrigeration unit fails.
A backup doesn't always hold the same temperature as the main system. For example, one manufacturer states that its backup holds a warmer range until the main system is repaired. Whether that's acceptable depends on what's being stored.
Some larger facilities keep extra storage space cold and empty so product can be moved if a unit fails. That spare space often fills up with product over time.
Why are alarms important for cold storage?
Backup equipment only helps if someone knows there's a problem. WHO guidance for pharmaceutical storage says alarms should be visible, preferably audible, and should automatically alert key staff by phone or text. It also describes early-warning alarms that go off before the temperature goes out of range.
How does backup power protect cold storage?
Backup power keeps the system running during a power outage. Without it, a backup refrigeration system won't help, because both systems need electricity. Many facilities use a standby generator. Some equipment also has batteries that keep alarms working when the power is out.
How often should a backup generator be tested?
CDC guidance for vaccine storage calls for testing generators every three months, servicing them once a year, and keeping at least 72 hours of fuel on hand. The guidance is written for vaccine providers, but it's a useful reference for other types of cold storage.
What doesn't redundancy protect against?
Backups can still fall short in the following situations.
Unnoticed failures. When a backup takes over, the temperature usually stays normal. If temperature is the only thing being monitored, staff may not know the main system has failed. The facility is then running without a backup until the problem is found.
Conditions that affect both systems. Hot weather and unstable power put extra strain on cooling equipment. They affect the main system and the backup at the same time. Similarly, a failed HVAC unit in the same room can do the same. For more on room requirements, see What Does Your Facility Need to Support Ultra-Low Equipment?
Untested backups. A backup that has never been tested may not work when it's needed.
Repair time. A backup gives time to repair the main system. The repair still requires a qualified technician and the right replacement part. WHO guidance on monitoring systems asks whether spare parts can be kept on site and expects 24-hour technical support.
What questions should you ask about a redundant cold storage system?
These questions apply to new systems and existing ones:
What happens to the temperature if the main refrigeration system fails?
Do the main system and the backup share anything, such as a power source or location?
How will someone know when a backup has taken over?
What keeps running during a power outage, and when was that last tested?
Who receives alarms at night and on holidays?
Where would replacement parts come from, and how long would they take to arrive?
The right amount of redundancy depends on what's being stored.
Frequently asked questions
What does N+1 redundancy mean?
N+1 means having one more unit than needed, so the system still has enough capacity if one unit fails. 2N means having a complete duplicate of every unit.
Is a backup generator enough to protect cold storage?
CDC's vaccine storage guidance says no. It recommends an agreement with an alternate storage site even when a generator is installed, because any equipment can fail.
What should a cold storage emergency plan include?
CDC's vaccine storage guidance provides an example. It says staff should know their after-hours responsibilities, and emergency procedures should explain how to access the storage units when the building is closed, including a building map and the locations of keys, spare batteries, and circuit breakers.
Does adding redundancy to a validated system require requalification?
It can. Adding or changing backup equipment is a change to a validated system, and it may require requalification. The facility's change control process determines what testing is needed.
If you have questions about redundancy for a new or existing system, we are here to help.
