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Are cold room trapped- person alarm systems safe enough?
Cold room alarms are meant to protect staff , yet incidents continue to occur. James Hibbert, Director at GB Controls, examines current system standards, common failure points and what engineers say is needed to improve reliability.
W "When
somebody walks into a cold room, are we satisfi ed because there is an emergency alarm on the wall? Or do we want to know that the alarm is continuously checking its own ability to protect them?"
alk into almost any commercial cold room or freezer, and you will usually fi nd a trapped-person alarm button. The principle seems reassuringly simple.
Someone becomes trapped inside, presses the emergency button, and an alarm sounds or a beacon illuminates, alerting others that help is needed. But there is an uncomfortable question that is rarely asked:
How do we know the alarm itself is actually capable of working when it is needed?
For equipment whose sole purpose is to protect human life, it is easy to focus on the visible function of the system – the button, the beacon, the sounder – while overlooking something potentially more important: whether the system can detect when its ability to perform that function has been compromised. That distinction matters.
A safety system is only useful if it remains available when someone needs it. A system that appears healthy but has developed a hidden fault can pose a particularly diffi cult safety problem because everyone may continue to assume that protection is in place.
The hidden risk Many conventional trapped-person alarm systems are designed with normally open circuits and relatively simple relay arrangements. These designs are inexpensive, familiar and straightforward to install. But simplicity can also introduce a weakness: a fault may occur without producing any obvious indication that the protective function has been lost. Consider what happens if a conductor breaks, a terminal loosens, corrosion develops, or a relay fails. From the outside, everything may appear normal. The beacon is off . No fault is displayed. No maintenance call is generated. The system can remain in this condition for months, potentially even years, until somebody presses the emergency button during a genuine emergency. Only then does the failure become apparent.
In functional safety engineering, this type of condition is
known as a dangerous undetected failure. A system intended to protect someone who may be isolated in a refrigerated environment deserves serious consideration.
20 October 2026 •
www.acr-news.com The important point is that the failure itself is not necessarily
dramatic. There may be no visible warning, no obvious electrical event and no immediate indication to operators that anything has changed. That is precisely what makes an undetected failure a concern.
Is testing the alarm enough? There is an important diff erence between demonstrating that an alarm works during a periodic test and being confi dent that it remains capable of working between tests. A routine test can provide useful assurance at the moment it is conducted. But what happens the following day? Or several weeks later? What happens if a component fails between inspections? If the system has no means of identifying that failure, the next test may be the fi rst opportunity to discover it. That creates a fundamental question for safety-system design: should the person responsible for the facility have to discover a fault by testing the emergency function, or should the system itself be capable of reporting that its protective function has been compromised? Modern safety engineering increasingly takes the latter approach.
Safety systems should monitor themselves One of the fundamental principles of safety engineering is that safety devices should not merely perform a function; they should continuously verify that they remain capable of doing so. This philosophy is already familiar in machinery safety, burner management systems, process industries and railway signalling. The underlying idea is straightforward. A safety system should not wait for an emergency to fi nd out whether something has failed. Instead, it should continuously monitor critical circuits, detect internal faults, supervise outputs and provide an immediate warning whenever its protective function may be impaired.
In the context of a trapped-person alarm, that could mean identifying problems such as loss of power, a failed relay, a disconnected alarm device, or an output circuit fault before anyone depends on the system.
The objective is not to make the system unnecessarily complicated. It is to make its condition visible. After all, there is
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