Safety-related evaluation of thermal operating stress on safety-critical equipment using the example of composite breathing air cylinders and lithium batteries.

Status:

completed 02/2024

Aims:

The aim of the project was to determine the influence of the real temperature load on breathing apparatus cylinders and lithium batteries in radio equipment in firefighting operations by rescue services and to be able to better assess their effect on ageing and service life time and the potential health hazards and to derive guidelines for action.

As part of this project, composite breathing air cylinders that have undergone different thermal ageing processes were systematically analysed with regard to their residual strength. On the other hand, lithium batteries used in radio equipment were analysed with regard to the effect of critical temperatures above which thermal runaway of the batteries can occur. Critical temperature-time profiles were determined for these two important components, lithium batteries and composite breathing air cylinders, the effects for the user were analysed using suitable methods and the resulting hazards for the wearer were assessed.

Activities/Methods:

As a methodical approach, the actual temperature profiles previously determined by literature research were first verified in real tests and the laboratory loads were derived on this basis. In order to take into account the properties of composite breathing air cylinders made of fibre composites, sample groups were subjected to different thermal loads and examined with regard to their residual strength reduction and in comparison to thermally unloaded samples from two representative samples from different manufacturers. In addition to the static burst tests, combined ageing and residual strength tests were also carried out on cyclic loaded cylinders.

Radio equipment were subjected to both static and cyclic loads with accompanying capacity measurements. The purpose of the static tests was to determine the maximum thermal load capacity of the batteries at which no failure occurs. In the cyclic tests, practical conditions were simulated as closely as possible in the laboratory. For this purpose, the batteries were repeatedly subjected to a load profile at a constant temperature and the residual capacity of the battery was measured after several intervals to determine the degradation.

Results:

The conclusion of the tests carried out on two representative models of breathing apparatus cylinders as part of this project is that, depending on the model, the thermal loads have a significant influence on the residual strengths of the breathing apparatus cylinders, but these can be regarded as uncritical for the safety of rescue workers. Higher thermal exposure is clearly recognisable, at least on the respiratory protection cylinders tested, and therefore these cylinders can be easily removed and replaced by the responsible equipment maintainers. It is therefore advisable to use lighter Type 4 breathing apparatus cylinders, as the thermal loads that occur during rescue operations are not critical, especially if established manufacturers with many years of experience are chosen. It is recommended to replace breathing protection cylinders that show visually recognisable thermal effects (colour changes, material melting, etc.).

The results on the radio equipment showed that the capacity determination can be used as a suitable criterion for the safety assessment of the batteries. It must always be ensured that the capacity measurement is carried out under constant conditions (same room temperatures, same measuring devices, etc.). It is recommended to replace the batteries when the remaining capacity is below 80%. A visual inspection of the radio equipment can be carried out as a quick and very simple check. The radio equipment used in the project showed deformation of the plastic casing when subjected to excessive loads.

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