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Abstract Rapid, low-cost evaluation of personal protective equipment (PPE) is important for providing widespread and easy-to-access testing of aerosols through and round masks and shields. Most related literature has focused on how well PPE protects the wearer, not reducing aerosol transmission to the environment. Few studies have compared the efficacy for particle escape at exhalation or inhalation of face masks and face shields. Measurements of particulate matter escaping through PPE could provide information regarding the efficacy on the wearer and on the surrounding of the PPE and guide the selection of appropriate PPE to wear in different conditions. Research grade particle technology devices are not widely available. Low-cost options which are simple to use may provide a practical alternative. In this study, we measured particulate matter with a diameter less than 2.5 µm (PM2.5) emitted by a manikin placed upright at the head of a stretcher. Measurements were made using three low-cost sensors and an Optical Particle Sizer (OPS) at distances of 2, 4, and 6 feet repeated at 0, 45, and 90°, given at a horizontal plane, with respect to the mannikin. The low-cost sensors correlated well with the OPS used as a reference method and may provide a simple, low-cost, widely available alternative.

Recently, Bennett et al. (Eur. J. Phys. 37:014001, 2016) presented a physically-motivated and explicitly gauge-independent scheme for the quantisation of the electromagnetic field in flat Minkowski space. In this paper we generalise this field quantisation scheme to curved spacetimes. Working within the standard assumptions of quantum field theory and only postulating the physicality of the photon, we derive the Hamiltonian, H ^ , and the electric and magnetic field observables, E ^ and B ^ , respectively, without having to invoke a specific gauge. As an example, we quantise the electromagnetic field in the spacetime of an accelerated Minkowski observer, Rindler space, and demonstrate consistency with other field quantisation schemes by reproducing the Unruh effect.