Procuring military equipment has become an extremely difficult task. Not only is there constant pressure to reduce expenditure, but performance requirements are increasingly hard to define as armed forces face growing and unpredictable threats such as civilian groups and militias using improvised weapons and ad hoc methods.
Since lives are at stake it can be tempting to impose excessively high requirements on the environmental performance of battlefield electronics, for instance by insisting on survivability for every possible hazard. As an example some new specifications for military electronics are calling for high resistance to Chemical/Biological/Radiological/Nuclear (CBRN) substances and harsh chemicals used for decontamination, in addition to more common requirements such as resistance to oils or fuel.
Proper sealing of electronic enclosures, using conductive gaskets, has a dual role both to prevent ingress of contaminants and as a shield against electromagnetic interference (EMI). A number of high-performance elastomers have been developed to meet such demands, offering a variety of properties that are optimised for particular environments and applications. Silicone-based elastomers for example, have an adequate resistance to oil, ozone or weathering. For equipment that may come into contact with chemicals such as hydrocarbon fuels or dilute acids, fluorocarbon-based elastomers can offer high performance.
To comply with requirements for surviving CBRN attacks, new types of filled EPDM elastomers have been developed for sealing and shielding. This class of material is engineered for good resistance to CBRN decontamination solutions such as super-tropical bleach (STB). One disadvantage of such compounds, however, is reduced resistance to oil, which can allow the seal to swell and soften, become misshapen and lose mechanical properties such as tensile strength. This can result in degraded sealing and shielding performance.
Unfortunately, natural limitations have so far prevented development of elastomeric compounds capable of providing high resistance to all chemicals likely to be encountered during day-to-day handling and in combat, in addition to CBRN decontamination chemicals. Instead, a sensible appraisal of equipment usage and anticipated hazards is needed to ensure optimum performance and serviceability throughout the lifetime of the equipment.
Since many types of electronic equipment are highly likely to be exposed to substances such as fuel or oil during daily use and conventional combat scenarios, it seems reasonable to place a high emphasis on resistance to these types of substances. It is also vital that equipment should be able to continue performing throughout the duration of a CBRN attack, so the seal must be able to perform adequately under such circumstances. Military-grade silicone and fluorosilicone formulas have high resistance to fuels and oils and could provide adequate resistance to some CBRN exposure even though their resistance to the decontamination chemicals is low.
An effective solution to this challenge is to specify decontamination procedures and controls that can reduce the risk of seals becoming degraded during or after decontamination. Western armed forces are known to have established detailed protocols for decontaminating personnel, vehicles and equipment. These protocols are sensitive to the threats posed by decontamination materials to sensitive items such as electronic equipment. They seek to minimise exposure to harsh chemicals by, for example, forbidding immersion or high-pressure spraying with decontamination solutions, and recommending that external surfaces are wiped down with a designated decontaminant then wiped with a damp cloth and finally dried. Inspection of any seals after decontamination is also stipulated.
Clearly there is a good understanding of the vulnerabilities of electronic equipment, among military end users. By drawing from this example, equipment specifiers and designers can gain advantages from taking an equally pragmatic approach when considering sealing and shielding in relation to environmental performance and CBRN resistance.