Thesis (Ph.D)

Characterisation of particulate matter originating from automotive occupant restraints


In 2012, in the UK, it was estimated that 6.5 million airbags required deployment at end of life. This process poses hazards such as that of occupational respiratory exposure to solid particulate matter (PM) effluents produced during the production of inflation gases for airbag deployment. To date methods for assessing effluent exposure has focused on vehicle occupants and not occupational exposures and has mainly centred on direct and static measurement of particle mass. This research programme evaluated existing methods of assessment and defined novel methods for more comprehensive characterisation. The methods were employed to characterise sub-micron PM effluents from driver airbags using non-azide, solid propellant and hybrid inflators. Testing was undertaken using a differential mobility spectrometer (DMS), gravimetric filtration, high speed photography and electron microscopy. A comparison of an effluent test tank and a vehicle of a comparable volume showed that the tank was able to replicate a vehicle environment and provide measurements with acceptable levels of inter-test variability with test duration of >900s. Characterisation of particle geometric mean diameter (GMD) and number concentration for airbag effluents showed that dominant particles were below 150nm in size, with smaller particles being emitted by hybrid airbags. Particle concentrations were also lower for hybrid airbags. By assessing transient behaviour it was identified that as time elapsed, concentration reduced whilst particle mean size increased. This data allowed identification of propellants used in airbags and a mathematical model was defined to describe effluent characteristics for each propellant employed. The particle sizes measured by DMS compared well with those obtained from TEM images which identified generally spherical particles, commonly accumulated as agglomerates. TEM also identified large concentrations of particles below the lower measurement range of the DMS, <5nm, and lower concentrations of larger particles >1μm. This research has provided verification of existing test methodologies and allowed a more comprehensive assessment of airbag effluents than previously presented in the literature.

Attached files


Wood, R

Oxford Brookes departments

Department of Mechanical Engineering and Mathematical Sciences
Faculty of Technology, Design and Environment


Year: 2013

© Wood, R
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