In response to the increased demands for ‘last-mile’ cold chain monitoring, electronic temperature indicators have emerged over the past decade as viable alternatives to their chemical counterparts, explains Jeff Hawkins, strategic marketing manager at Sensitech Inc.

Temperature indicators based on the thermal properties of chemical compounds (chemical indicators) have been commercially available for many years, providing accept/ reject information for perishable goods within the food supply chain. While many believe chemical indicators may fall short of compliance with global regulations and industry best practices, these devices have, over time, migrated to last-mile cold chain applications in the life science market.

In response to the increased demands for last-mile monitoring, electronic temperature indicators have emerged over the past decade as viable alternatives to chemical indicators, providing superior performance and functionality. In addition, manufacturing costs of electronic devices have dropped substantially, enabling cost-effective deployments in a wide variety of applications. Considerations for temperature indicator usage include:

Time and Temperature Accuracy

Typical temperature accuracies for chemical indicators are ±1-2ºC, as opposed to electronic devices providing accuracies of ±0.5-1ºC. Time accuracy specifications for chemical indicators vary widely with specifications such as threshold indication after ‘a minimum of 30 minutes’ or ‘within 15 minutes’ of exposure above/below set-point temperature. For electronic indicators, typical time accuracies are of the order of ±0.01% of elapsed time (less than a five-minute error per month of operation). Some chemical time-temperature indicators (TTIs) provide evidence of the accumulated effects of temperature exposure. The dynamic temperature response of TTIs is governed by the Arrhenius equation, more specifically the activation energy (EA) of the temperature-sensitive material. TTI manufacturers strive to emulate the dynamic temperature effects of the monitored product via matching EA values within the indicator. In practice, this matching is often sub-optimal, leading to substantial inaccuracies.

Device validation

Electronic indicators can be validated prior to activation and deployment. The technology enables every indicator to be tested for accurate operation during the manufacturing process, thereby establishing the veracity of the measurement for 100% of device production. Chemical indicators cannot be validated in this fashion as validation or testing at operational time/temperature thresholds would be destructive. In addition, electronic indicators can typically be post-use validated by the manufacturer. Chemical indicators cannot be reset and tested after initial activation and use.

Custom threshold alarm settings

Most electronic indicators can be customised to fit unique transport conditions dictated by product storage requirements, packaging/pack out parameters and transportation route variability. Chemical indicators are generally offered in a limited number of timetemperature threshold or activation energy variants. Furthermore, most electronic devices can be programmed with several independent time-temperature alarm conditions. As a result, a single device can be deployed to monitor both high and low temperature limits, eliminating the need to procure, stock, and deploy multiple indicator devices for each shipment.

Interface ambiguity

Chemical-based TTIs incorporate user interfaces that are dependent on colour-matching of the reactive material or the determination of a ‘migration’ distance of the reactive material relative to a graded time scale, necessitating subjective interpretations of the results. In contrast, electronic indicators integrate user interfaces and displays that offer clear, unequivocal results of time-temperature alarm conditions.

Pre-deployment storage and shipment environment

Many chemical indicators must be stored and shipped within controlled conditions prior to deployment. In comparison, electronic indicators offer broad storage and shipment temperature ranges prior to deployment since they are commonly supplied inactivated and are therefore unaffected by temperature conditions prior to start. In addition to these onerous storage and shipping conditions, some chemical indicators require specific temperature pre-conditioning protocols to ensure proper operation.

In summary, these attributes highlight many of the advantages of electronic temperature indicator technology for ‘last-mile’ cold chain monitoring applications. Viewed holistically, electronic indicators offer effective, accurate, and cost-efficient temperature monitoring in support of global regulatory requirements.


Cargo monitoring devices defined

When Delta Airlines stated that it would no longer accept cargo with temperature monitoring devices, it did not define the rules concerning lithium batteries. Sensitech EMEA worked with US authorities to provide a review of current regulations.

On 25 November 2008, Delta Airline’s cargo department issued a memo stating that they would no longer accept cargo with temperature monitoring devices. Delta did not interpret the US Department of Transportation (DoT) Pipeline and Hazardous Materials Safety Administration – 49 CFR Hazardous Materials, Transportation of Lithium Batteries – to pertain to devices used to monitor cargo.

At the centre of the confusion was that the regulations clearly covered batteries as cargo, as bulk and within equipment as well as batteries in carry-on or checked passenger luggage, but was not interpreted as being explicit in covering batteries contained in devices that monitor cargo.

Working to address this perceived ambiguity, Sensitech requested a formal interpretation from the US DoT. Sensitech believed temperature monitors should be covered under the current regulations and as such would qualify for the exceptions provided for small lithium batteries under Special Provision 188 – given the characteristics of the batteries used in Sensitech’s devices.


On 4 December 2008, Edward T Mazzullo, director, Office of Hazardous Materials Standards Pipeline and Hazardous Materials Safety Administration, US DoT, agreed with Sensitech’s position. ‘The devices are offered for transport and transported in commerce,’ he stated in a letter. ‘Thus, to the extent they contain hazardous materials, they are subject to the applicable provisions of the Hazardous Materials Regulations (HMR). Based on the information Sensitech has provided, we agree with the assessment that these devices qualify for the exceptions provided for small lithium batteries under SP 188.’

While this letter specifically mentions Sensitech’s products, the US DoT’s position clarifies this ruling to include all temperature monitoring devices provided that the device in question complies with the HMR regulations. It is important to note that it is up to each device manufacturer to ensure that they comply with the regulations.

International regulations

While the US DoT regulations generally apply to US-flagged air carriers, it is important to recognise that the International Air Transport Association (IATA) Dangerous Goods Regulations (DGR)/ International Civil Aviation Organization (ICAO)’s Technical Instructions are followed by non US flagged carriers. IATA’s documentation is often described as adding important and valuable operational details and is commonly considered a ‘field guide’.

Small lithium metal and lithium ion batteries are exempt from most of the requirements of the IACO Technical Instructions and IATA DGR, provided that they comply with all of the requirements set out in Part 1 of Packing Instructions 968, 969, and 970 for lithium metal batteries. Again, Sensitech’s devices fall into this category and meet all of the conditions outlined in the packing instruction. Sensitech received formal approval from the Safety Standards Department at IATA on 22 January 2009.

Electromagnetic testing

A related point of contention has been electromagnetic compatibility. The FAA requires that devices operating on a flight be tested to ensure there is no interference with flight systems (see FAA Advisory Circular 91-21.1B). Delta’s engineering department worked closely with Sensitech and the FAA on this topic and Delta issued a formal approval of Sensitech’s devices on 27 January 2009.

As part of the approval process, Delta is expected to require that shippers document all shipments containing approved temperature monitoring devices and specifically indicate the manufacturer and model number of the approved device on the air waybill.

Sourcing quality

It is critical for a shipper to source products from a high-quality supplier that has completed the necessary testing and documentation to ensure that their products comply with global regulations. This can be an extremely time-consuming and costly process and requires that the manufacture have the necessary quality systems and validation protocols in place to ensure compliance.

Sensitech EMEA is a business unit of Carrier Corp, the world’s largest provider of heating, air conditioning and refrigeration solutions with operations in 172 countries.