Introduction
Entry to freight containers represents a significant hazard to staff responsible for inspection, stuffing or destuffing because of the large number of airborne chemicals that can be present. Research in Germany and the Netherlands found hazardous levels of gases and vapours in around 20 percent of all containers and this level of contamination is now accepted as commonplace.
It is therefore necessary to examine containers before entry and this work is usually conducted with a wide variety of gas detection techniques in order to be able to assess, individually, all of the substances of greatest concern. However, a Dutch firm of health and safety consultants, Reaktie, has employed Fourier Transform Infra Red (FTIR) gas analysis to dramatically improve the speed and effectiveness with which containers are assessed, because this technology enables the simultaneous measurement of the 50 gases of most concern.
Chemical hazards
There are two potential sources of hazardous chemicals inside cargo containers; fumigants and chemicals that arise from the goods or packing materials.
Fumigants are applied to goods to control pests and microorganisms. Cargoes most likely to have been fumigated include foodstuffs, leather goods, handicrafts, textiles, timber or cane furniture, luxury vehicles and cargo in timber cases or on timber pallets from Asia.
According to the IMO's international regulations, ‘Recommendations on the safe use of pesticides in ships’, fumigated containers and ship cargoes must be labeled giving specifications about dates of fumigation and the fumigation gas used. Furthermore, appropriate certificates are necessary and these records have to be forwarded to the port health authorities. However, absence of marking cannot be taken to mean fumigants are not present. Containers marked as having been ventilated after fumigation may also contain fumigant that was absorbed by the cargo and released during transit. There is also concern that fumigants may be retained in the goods and subsequently present a hazard to logistics providers, retail staff and consumers.
Common fumigants include Chloropicrine, Methyl bromide, Ethylene dibromide, Sulfuryl fluoride and Phospine. However, with over 20 years of experience testing gases in containers, Peter Broersma from Reaktie says, “While the fumigants are highly toxic, the number of containers exceeding Occupational Exposure Limits (OEL) due to other chemicals is much greater and the number of ‘failed’ containers is likely to rise as more containers are tested, detection methods improve and new gases are identified.”
Containers often travel for extended periods and experience a wide range of temperatures. It is therefore not surprising that unsafe levels of gases should accumulate in the confined space of a container. Peter identifies the typical sources of gases over their OELs as follows: solvents from glues used to produce clothing, accessories and shoes; 1,2-dichloroethane from plastic products; PVC; blister packaging; formaldehyde found in cheap furniture but also in used pallets and lashing materials; solvents and formaldehyde from poly-resin products; carbon monoxide from charcoal and natural products; carbon dioxide from natural products and ethylene oxide from medical equipment sterilised with ethylene oxide. Also solvents including Benzene, Toluene, Ethylbenzene and Xylene (BTEX) in Christmas and decoration products; flammable gases from disposable lighters; ammonia in household equipment with Bakelite parts; Volatile Organic Compounds (VOCs) from fire blocks; pentanes and hexanes from consumer electronics and phosphine/arsine from natural minerals such as ferrosilicon.
Inspection procedures
Major ports have strict regulations in place to protect against potential hazards in cargo containers. In general terms, every incoming stream of products has to be checked for dangerous gases and if one or more gases are detected during the preliminary investigation, all of the containers from this specific producer must be checked. If no gases are detected, it may be possible to only conduct random tests a few times per year. If it is necessary for customs staff to enter a container, all containers must first be tested and if necessary de-gassed.
Gas detection
Since there are a large number of gases that might be present inside a container, the traditional approach to monitoring has been either to employ a wide range of instruments or to use chemical stain tubes for the most common gases, or a combination of both.
Chemical stain tubes provide a colorimetric assessment of an individual gas, typically with an accuracy of +/- 15 percent. Different tubes are available for many gases and results can be obtained between five seconds and 15 minutes depending on the test. Once a result has been obtained, the tube itself is hazardous waste and must be disposed of. Historically stain tubes have been popular because the cost per test is low. However, the number of tubes that have to be employed in order to demonstrate that a container is safe can be prohibitively expensive and time-consuming to employ.
Instrumental gas analyzers such as electrochemical sensors, that measure either a single gas or a small number of gases impart a similar level of risk to stain tubes because of the possibility of missing or failing to measure a harmful gas. Deploying multiple instruments also presents practical problems because each will require maintenance and recalibration in addition to a power source or recharging. Nevertheless, Reaktie for example, would normally conduct a preliminary assessment with a photoionization detector (PID) for total VOCs; a Lower Explosive Limit (LEL) combustible gas sensor and handheld electrochemical sensors might be employed for toxic gases such as carbon monoxide, phosphine, ammonia and ethylene oxide. A FTIR analyzer would then be employed to measure 50 target gases simultaneously in a test that would take approximately three minutes. This ability to measure compounds individually is important because, for example, whilst a PID gas detector measures total VOCs, it does not provide an individual value for, say, benzene, which is a known carcinogen.
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