Applying CO₂ leak detection in food retail

Tom Burniston, SAMON’s Marketing Director and Group Product Management Lead for Safe Monitoring Group, says the choice of detection systems should be guided by response time and operating temperature.

The developments and changes in regulations, the phase-down of HFC refrigerants, and the ongoing development of refrigeration technology see carbon dioxide (CO₂) increasingly being used as a refrigerant in a wide variety of applications. This includes applications such as:
•    Supermarkets
•    Convenience stores
•    Cold rooms
•    Walk-in freezers
•    Industrial cold storage
•    Food manufacturing
•    Food processing

CO₂ has a significantly lower global warming potential (GWP) than HFC refrigerants, making it less environmentally harmful than many of the gases previously used in these refrigeration applications. Most of these gases, such as R134a and R404A, are beginning to be phased out of use due to their environmental impact. This is driven by regulations put in place to drastically reduce the use of HFCs and their associated impact on the Earth’s climate. In Europe, the F-Gas Regulation (EU) 2024/573 has an ambitious goal to reduce the amount of HFCs placed on the market by 98% by 2050 (compared to 2015). 

In the US, the refrigeration sector is addressed directly by the American Innovation and Manufacturing Act. The over-arching goal of the programme is to phase down HFC production and consumption by 85% from baseline levels by 2036. 

This creates a great driver towards CO₂ becoming an increasingly attractive option for use when balanced against the requirements and limitations resulting from implementation of the regulations. Furthermore, the manufacturers of refrigeration systems continue to develop a growing range of ever more efficient and cost-effective CO₂ refrigeration system options, enabling their wider adoption into commercial applications.

Why are CO₂ detectors needed?

Although comparatively beneficial for the environment relative to HFCs, in high concentrations CO₂ can be dangerous to humans because it is both a toxic gas and an asphyxiant gas. Refrigeration systems using CO₂ also operate at high pressures, sometimes as high as 2,000psig, which means that if a leak occurs the gas can escape at a high rate, quickly creating a dangerous atmosphere.

The effects of CO₂ are shown in Table 1 below:

CO2 concentration in air (ppm)	Effects
370	Atmospheric level
5,000	Long-term exposure limit – 8 hours TWA
15,000	Short-term exposure limit – 15 minutes, some physical discomfort
30,000	Respiration difficulties, headache, dizziness, nausea
40,000	IDLH limit (Immediate Danger to Life & Health)
100,000	Loss of consciousness, death
300,000	Quick death

 

Refrigerant safety standards, such as EN 378-1:2016+A1:2020 and ASHRAE 34-2022, establish exposure levels critical for assessing the safety of refrigerant systems and determining instances where refrigerant leak detection becomes necessary. These standards typically encompass scenarios requiring detection in machinery rooms and refrigerated spaces like cold rooms and walk-in freezers. Moreover, larger refrigerant charge sizes of the type typically found in a large supermarket escalate the likelihood of mandated leak detection in expansive areas, such as storage freezers.

Given the nature of refrigeration systems, leaks may occur over time due to various factors such as inadequate maintenance, mechanical wear, accidental damage, or improper installation. Highly pressurised systems (such as those using CO₂) are particularly susceptible to these issues, significantly heightening the risk of leaks.

The potential dangers of CO₂ in a food retail application are very real. For an example in a refrigeration system using CO₂ as a refrigerant, in a typical walk-in cold room with a volume of 25m3 and a rate of one air exchange per hour we can calculate that a leak rate of 500g/hr will create an atmosphere containing 40,793ppm of CO₂ in just 250 seconds. 

That surpasses the level of 40,000ppm at which CO₂ presents an immediate danger to life and health according to OSHA guidelines.

In addition to safety concerns, CO₂ refrigerant leaks pose significant economic risks, potentially leading to inadequate cooling that fails to meet essential food safety standards or, in extreme cases, complete system failure. Such occurrences can result in food spoilage, leading to significant waste and profound economic consequences. For high-value products like dry-aged beef or luxury ice cream, a single unaddressed refrigerant leak could incur significant costs.

Selecting an appropriate CO₂ leak detector 

Carbon dioxide detection serves a multitude of purposes across diverse domains, spanning from ensuring indoor air quality (IAQ) to safeguarding occupational environments and monitoring refrigeration systems. However, the suitability of CO₂ monitoring devices varies significantly depending on the intended application, particularly when it comes to leak detection in refrigeration settings.

In navigating the selection process for a CO₂ leak detector, two pivotal factors demand particularly careful consideration: response time and operating temperature.

Given the potential for CO₂ leaks to rapidly escalate and create hazardous conditions, the responsiveness of a refrigerant gas detector becomes paramount. Instruments tailored for continuously monitoring gradual shifts in atmospheric CO₂ levels, commonly utilized in IAQ contexts, may lack the swift response required for effective leak detection. 

In leak detection scenarios, where swift action is crucial to prevent the onset of dangerous situations, a rapid response time is not only indispensable, but is mandated by refrigerant safety standards. Consequently, it is incumbent upon operators to thoroughly evaluate not only the stipulated response time of the sensor embedded within a leak detector but also, and perhaps more significantly, the overall response time of the instrument as a cohesive unit.

It's noteworthy that the design intricacies of detection devices can significantly influence the rate at which gas reaches the CO₂ sensor. For instance, configurations that afford direct exposure of the sensor to the monitored atmosphere typically yield swifter response times. Conversely, in certain instrument designs where gas must traverse a capillary tube before reaching the sensor, the response time may be considerably extended, potentially undermining the efficacy of the sensor's inherent responsiveness.

Therefore, ensuring a full alignment between the response time of the gas detector and the specific requirements of the application is of paramount importance to fully harness the intended benefits of the device. This necessitates a nuanced evaluation of the instrument's design and capabilities to ascertain its suitability for its intended use.

Furthermore, beyond response time considerations, the operating temperature range of the CO₂ detector warrants careful scrutiny. Given the diverse operational environments encountered in refrigeration settings, including extremes of temperature, it is imperative to select a detector capable of reliably functioning within the designated temperature range.

In essence, while CO₂ detection technologies offer invaluable insights and capabilities across a spectrum of applications, when selecting systems for leak detection in refrigeration systems, a discerning approach to device selection, taking into account factors such as response time and operating temperature, is indispensable in ensuring optimal performance and ensuring the safety of personnel working with and around the refrigeration system.

Implementing CO₂ detection: best practices and considerations

When it comes to effectively detecting CO₂, understanding the behaviour of this gas is essential. CO₂ is marginally denser than air, which means it tends to descend towards the ground over time. Consequently, for optimal detection, it's recommended to install gas detectors at lower levels, approximately 20cm above the ground. However, specific circumstances may warrant deviations from this standard approach.

For instance, in environments like cold rooms, where airflow dynamics differ, positioning the gas detector on a side-wall within the return air flow to the evaporator is often considered the most effective strategy. This positioning ensures that any CO₂ present is promptly detected, safeguarding the integrity of stored goods.

Strategic placement of gas detectors near potential leak sources is another critical aspect of effective CO₂ detection. These sources include valves, flanges, joints, and pressure reducers, where leaks are more likely to occur. Additionally, positioning detectors in close proximity to areas with a high concentration of refrigerant, such as compressors, storage tanks/cylinders, pipes, and conduits, enhances detection sensitivity.

Incorporating considerations for airflow patterns and ventilation is also vital. Both natural and mechanical ventilation systems can impact the dispersal of leaked gas into the environment. Since CO₂ disperses relatively slowly, especially in confined spaces, ventilation plays a crucial role in moving gas clouds and aiding detection. Placing gas detectors within airflow paths ensures comprehensive coverage and maximises the likelihood of early detection.

It's worth noting that determining the optimal number of sensors and their precise locations for a given application is not governed by universal rules or standards. Instead, it requires careful consideration of the specific environmental factors and potential risks present. Therefore, the guidance provided serves as a framework to support installers in making informed decisions tailored to each unique situation.

Ultimately, adherence to all relevant local, state, and national regulations is paramount. Compliance ensures not only the safety and security of the premises but also safeguards against potential liabilities. By implementing CO₂ detection systems in accordance with best practices and regulations, businesses can mitigate risks effectively and maintain operational continuity.

Effective CO₂ refrigerant gas detection

The use of CO₂ in food retail applications presents challenges for operators, some of which are akin to those faced when using HFC refrigerants, and some of which are new. One clear way to hep mitigate the safety risk posed by CO₂ leakage is the implementation of a well-designed, correctly implemented refrigerant gas detection system.

This begins with the selection of appropriate sensors integrated within a refrigerant gas detector designed for the application. A well-planned installation, taking into account the behaviour and characteristics of CO₂ when it leaks, can deliver a fully effective refrigerant leak detection system forming part of the wider refrigeration safety system design.