Cold chain monitoring devices: indicators, data loggers, and real-time devices

Five types of monitoring device in WHO's guidance

WHO's technical supplement on monitoring in transport sorts the devices in common use into five types. Four travel with the product:

Chemical indicators and integrators

labels, usually on a paperboard base, that change appearance irreversibly with temperature. A threshold indicator responds once a set temperature is crossed, upward or downward; a progressive indicator registers repeated events cumulatively. A time-temperature integrator measures accumulated heat rather than a single spike; the vaccine vial monitor is one.

Electronic temperature indicators

small battery-powered devices with a sensor that show whether an alarm limit was breached, typically on a display, usually without a full record that can be downloaded.

Electronic data logging monitors

what most people mean by a data logger: a portable device that measures and stores temperature at set intervals, with programmable alarms, and produces reports and graphs.

Electronic data integrators

hybrids that show a go or no-go result like an indicator and keep the record of a data logger.

The fifth is built in rather than packed: the temperature monitoring and event recording systems fitted to refrigerated vehicles, which WHO notes may be monitored remotely by satellite link.

The supplement has no separate type for devices that report while the shipment moves. In its terms, such a device is a data logging monitor that also transmits its record.

Indicators: whether a limit was crossed

An indicator answers one question at a glance and needs no equipment to read, so it can go on every carton or pack. WHO's comparison of device types is just as clear about what an indicator cannot do:

No time-specific record

an indicator does not show when an excursion happened or how long it lasted.

Not an analytical tool

a threshold indicator gives no data to trend a lane or investigate a cause.

One limit at a time

a chemical indicator watches a single limit, so an upper and a lower limit together take two.

Read by eye

how someone reads a gradual color change can be affected by human factors.

WHO's guidance is that the result of an indicator is written on the product's arrival report and used to decide whether the consignment goes into storage or into quarantine until it has been investigated. An indicator can start that quarantine, but it cannot by itself show how far or how long the product was out of range, which is what the assessment against stability data needs.

The kinds of indicator, from threshold labels to vaccine vial monitors, are covered in our guide to time-temperature indicators.

Temperature data loggers: the full history

A temperature data logger is an electronic device that measures temperature at a fixed interval and stores every reading, so the record shows the whole trip: when the product left its range, how far it went, and how long it stayed out. That is the record a temperature excursion is assessed on, and the one a lane, a route shipped again and again, is trended on.

Data loggers are read in different ways, and the way decides how quickly the record reaches the person who needs it:

Cable or USB

the device is plugged into a computer at the destination, often producing a PDF report. The record exists only once someone has done so.

Short-range wireless

the device is read with a phone or a reader over near-field communication (NFC) or Bluetooth, which saves opening the package but still needs someone or something nearby.

Cellular or satellite

the device sends its readings over a network during the trip, which is what makes it a real-time device.

They come single-use or reusable, and the rules treat the two differently. WHO expects a single-use device to arrive with a manufacturer's calibration certificate covering its whole range, because it cannot be recalibrated, and a reusable device to be calibrated against a traceable reference once a year unless otherwise justified.

Real-time devices: the record while the shipment moves

A real-time device, also sold as a real-time data logger or a tracker, sends its readings during the trip, over the cellular network or by satellite, so an alarm can be seen while the excursion is still happening, when a pallet can still be moved off an apron or a container's power restored. When the shipment arrives, its record is already complete.

Real-time is a matter of when the data arrives, not of whether a device is thrown away: single-use devices that report in transit exist alongside reusable ones. What a real-time device adds is only as useful as the response to its alarms, so the question to ask of any real-time setup is who is watching, at what hours, and what they are allowed to do.

No regulation requires real-time monitoring. The guidance requires that conditions be monitored, recorded, and demonstrable, and the case for seeing an excursion early is a risk argument, which our guide to temperature excursions sets out. We make it, with the cases where it does not pay, in Why real-time temperature monitoring, and when it isn't worth it.

Humidity, light, and location

Some devices record more than temperature. Humidity is the most common addition, though WHO notes it is generally considered to have a minimal effect on products in hermetically sealed primary packaging inside a shipping container. Light can show that a package was opened in transit, and location shows where an excursion happened, which is what an investigation into its cause needs first.

For frozen products on dry ice or in liquid nitrogen, the device usually measures through an external probe placed in the payload, because the device itself cannot sit at those temperatures. The rest of what those shipments require is in our guide to shipping with dry ice.

Passive versus active monitoring: two meanings

Much of the confusion in this subject comes from two words that are used for two different things.

Packaging

a passive system is an insulated shipper that holds a finite amount of preconditioned coolant, such as gel packs, phase change material, or dry ice, in WHO's definition. An active system cools with its own powered refrigeration unit, as a refrigerated container does.

Monitoring

a passive device keeps its data until it is read, while an active device sends its data to a central point as it goes. The World Food Programme's logistics guide uses the words this way, and describes data loggers as usually passive.

The two are independent. A passive shipper can carry a real-time device, and an active container can carry a single-use data logger that is read only on arrival. When someone says "passive monitoring", it is worth asking which of the two they mean.

Choosing a device by what its data has to decide

WHO's advice is to choose the device from a user requirement specification: first decide what the data is for, then pick the technology. It names two purposes, deciding whether to accept or reject a shipment, and analyzing the transport system afterwards to find its weak points. How the device types compare on the questions that follow:

WHO also asks for the choice to weigh ease of use and how the device fits into the rest of the supply chain. Some devices need extra software or hardware, such as a docking station, before they can be read, which may not be acceptable in every case.

The choice is often a combination rather than one device: a recording device for the shipment, and indicators on the cartons and packs that travel on after the pallet is broken down.

What the rules ask of any device

Written into the agreement

WHO generally makes the shipper responsible for temperature compliance in transport, and expects the service level agreement with the carrier, or the shipper's own written procedures, to state which monitoring devices are used, when and where they are placed, and how their data is collected, reported, and stored.

Fit for the job

whatever device or system is chosen, WHO asks that it be accurate, stable, reliable, and validated, and that its calibration cover the whole temperature range it is used over.

Trained people

WHO expects the staff responsible for transport to know the device types, their strengths and weaknesses, and how to operate them and read and interpret their data.

Calibration

the EU Guidelines on Good Distribution Practice (GDP) ask for transport temperature monitoring equipment to be maintained and calibrated at regular intervals, at least once a year. WHO adds the rules for single-use and reusable devices set out above.

Accuracy

WHO lists an accuracy of ±0.5 °C as a feature of the electronic device types. It is a point of comparison in its guidance, not a limit set for every device.

Records

WHO expects downloaded time and temperature data to be kept for at least three years in most cases, in a form that can be retrieved, and accepts a secure web-based repository.

Electronic records

where the monitoring record is a regulated quality record (a GxP record) kept electronically, the US Food and Drug Administration's rule on electronic records, 21 CFR Part 11, and Annex 11 of the EU good manufacturing practice (GMP) guide set expectations for the system that holds it, including validation and audit trails.

How these rules sit within the wider distribution framework is in our guide to good distribution practice, and what the electronic-record rules ask of the system that holds the data in our guide to data integrity for temperature records. Battery-powered devices that fly have rules of their own, covered in our guide to pharmaceutical transport.

Where Controlant fits

Controlant's Saga devices are reusable real-time devices. They report over the cellular network while the shipment moves, on a set schedule and at once on an excursion, and Controlant collects, inspects, recharges, and recalibrates them between trips. Our MARS team watches shipments 24/7/365 and acts on alarms by the customer's work instructions. For the cartons and packs that travel on after the pallet break, labels and indicators carry the evidence further. How the approaches compare, side by side, is on our page comparing cold chain monitoring approaches.