The Sydney siege: courage, compassion and connectedness

To the Editor: Raphael and Burns highlighted the strong police response to the hostage situation in Sydney in 2014.1 Diversionary devices, such as the flash-bang grenades used in Sydney, have been increasingly used to distract and disorientate people in civilian hostage and riot situations internationally. While not intended to cause permanent damage, there are risks associated with their use.

Flash-bang grenades deflagrate using a powdered blend of aluminium, magnesium and ammonium perchlorate, which generates a spontaneous explosion. When initiated, illumination is produced through oxidation of the components, resulting in heat exceeding 38°C, a blast reaching 180 decibels and a brief flash of 1–6 million candela (up to 600 million lux) within a distance of about 1.8 m.2

The intense flash results in temporary bleaching of the photoreceptors in the eye. Ocular injury can occur if the flash-bang grenade explodes at close range, with possible thermal or mechanical damage. Other more powerful devices, producing a similar intensity of unidirectional light, have resulted in vision loss similar to that seen with laser weapons.2

Temporary hearing loss and aural pain results from a single or multiple blast of loud noise between 140 and 170 decibels. Damage to the sensitive structure of the inner and middle ear can result in hearing loss and tinnitus.3 Perilymphatic fistula of the inner ear may occur, necessitating immediate assessment and possible surgical treatment.4

Premature deflagration can also cause injury to the operator.5 As these devices continue to be used in civilian situations, it is important to remain aware of any potential hazards, to both the operator and bystanders.