It has been estimated that there are more than 17 million shipping containers in the world, and at any time about one third of them are on ships, trucks, and trains. Over a single year, the total number of container trips has been estimated to be around 200 million.
The air quality inside containers varies enormously, depending on the goods, the packing materials, transit time, temperature, humidity and the possible presence of fumigants. Consequently, many containers contain dangerous levels of toxic gases and represent a major threat to port and transport workers, customs officials, warehousemen, store employees and consumers. If the gas concentration exceeds the threshold limit value (TLV) the container has to be ventilated. It is therefore essential that risks are assessed effectively before entry is permitted.
Solvent vapours and most fumigants, whilst harmful, can be detected by the human nose. According to Wim van Tienen, director of Van Tienen Milieuadvies B.V., which offers gas analysis and safety advice, he said while some gases are odourless, some have a high odour detection threshold, meaning you can only smell the substance in high concentrations. He offered an example of ethylene oxide, commonly used as a sterilant in relation to medical devices. It is extremely toxic and has a low TLV of 0.5 ppm. However the odour threshold limit of ethylene oxide is 500 ppm, so detection with instrumentation is essential.
The wide variety of potential contaminants represents a technological challenge to those responsible for testing, because if testers seek to detect specific gases, they risk failing to detect other compounds. It is also not practical to test every single container, so logical procedures must be established in order to minimise risks.
Limitations of current gas detection methods
Traditionally, container gas detection was carried out with field measurement techniques like gas detection sensors and tubes. These approaches are complicated, costly, time-consuming, and impossible to cover all risks. With sensors and tubes, only a limited number of compounds can be measured specifically. Furthermore, the accuracy of detection tubes is poor and they can suffer from cross-sensitive reactions by interfering substances.
Technologies such as photoionization detector (PID) respond to a wide variety of organic compounds, but they are not selective and unable to detect commonly found substances with high ionisation potentials such as 1,2-dichloroethane and formaldehyde. Wim does not, therefore, believe that traditional measurement techniques are the best approach for covering all risks. He warns that in order to test for the most common gases, it would be necessary to utilise a large number of tubes for every container, but this would still risk failing to detect other compounds and would be very expensive.
It is possible to speciate organic compounds when using a Gas Chromatograph (GC), but the number of compounds that can be tested is limited, and the use of a GC necessitates frequent calibration with expensive standard gases.
Alternative technology
As a result of the problems associated with traditional gas detection techniques, Wim was keen to find an alternative technology. In 2013, he became aware of the portable FTIR multigas analyzers (DX4040) from the Finnish company Gasmet Technologies. The instrument is able to both detect and measure hundreds of compounds simultaneously; with this technique all inventoried high risk substances, such as ethylene oxide and formaldehyde, are always measured in real-time. Gasmet’s distributor Reaktie, also developed a library of over 300 gases for the container monitoring application.
The major advantage of the Gasmet FTIR analyzers is the simultaneous multigas analysis capability. Testing works can be made faster, more efficient and cost-effective, because the analyzers are small, lightweight, relatively simple to run, and no calibration is required other than a quick daily zero check with Nitrogen. More containers can be tested per day and by testing for such a large number of target compounds, this can dramatically help lower the risks to staff. The negligible requirement for service, calibration and consumables, means that the ongoing cost of monitoring is kept minimal.
According to Wim, most of the gases that are detected and measured by FTIR analyzers are cargo related. He says that off-gassing during shipment is the greatest problem, producing volatile organic compounds (VOCs) such as Toluene, Xylenes, MEK, 1,2 dichloroethane, blowing agents such as isopentane, and butanes from the packing materials and products. Formaldehyde, which evaporates from glued pallets, is most commonly found. On the other hand, less frequently found fumigants, such as sulfuryl difluoride and hydrogen cyanide are also always picked up with the FTIR analyzers.
Container management
The need for container gas testing is driven by the employers’ duty of care for employees, which is embedded in international health and safety regulations. Companies receiving containers must investigate whether employees that open or enter containers, may be exposed to the dangers of suffocation, intoxication, poisoning, fire or explosion. In order for employers to protect staff from these hazards, a risk assessment is necessary, coupled with an effective plan to categorize and monitor container flows. Hence an effective testing strategy must be developed. For instance, if a flow of containers from the same source containing the same goods and packing materials is found to be safe, the number of containers being tested within that flow can be reduced. Similarly, if toxic gases are identified regularly in a container flow, the frequency of testing will be increased.
Once a container has been found to contain toxic levels of a gas or gases, it is necessary for that container to be ‘de-gassed’ which is a service that Van Tienen Milieuadvies provides. The process involves fitting a powerful ventilator to the door and capturing the gases with activated carbon. Once degassing is complete, it is important that the container is unloaded promptly, because the gases involved will re-accumulate quickly in a closed container, resulting in the need for repeat testing.
Wim estimates that around 10 percent of containers contain toxic gases. This means that hundreds of thousands of containers are travelling the world, representing a major risk to anyone that might enter or open them, so it is vital that effective testing strategies are in place wherever that risk exists.
Wim explains that Van Tienen combines the Gasmet DX4040 measurements with risk analysis, which provides cost reduction for clients, due to the fact that measurement frequencies in safe flows can be reduced significantly. Having Lloyd’s Register Quality Assurance (LRQA) certification for the procedures developed by the company also help demonstrate compliance with occupational health and safety legislation.
Looking forward, Wim believes that the use of Gasmet FTIR will expand rapidly around the world as the risks associated with containers become better understood, and as employers become more aware of the advantages of the technology.
Source: http://www.logasiamag.com/2017/03/gas-matters-freight-container-toxic-gas-analysis/
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