Problem Statement

Large public gatherings in India, including temple processions, political rallies, festivals, concerts and railway platforms, can reach densities where people lose control of their movement. Above roughly five people per square metre, crowds behave like a fluid, creating pressure waves. Deaths often result from compressive asphyxia, when pressure prevents the chest from expanding. Static crowds silently compress, while moving crowds crush people when the front stops but the rear continues.

Solution

Cameras divide a crowd into a grid and score every zone for crush risk in real time. Where the crowd is standing we measure density, and where it is moving we measure speed. When a zone crosses the limit, a drone flies there with a guiding light and a 3 kHz pulse.

In Detail

Crowd crush kills by compressive asphyxia. Above roughly 5 people per square metre a crowd behaves like a fluid, pressure waves travel through it, and the chest can no longer expand. We treat this as one problem with two trigger conditions. Overhead cameras divide the venue into a grid and score every cell continuously. Where the crowd is standing still, the danger is local compression, so we measure people per square metre per cell and act at 4 per square metre, or sooner if a cell gains 1.5 per square metre in a minute. Five per square metre is already the emergency, so alarming there leaves no time to respond. Where the crowd is moving, it flows along a route like a fluid and density alone is not enough: the danger is a velocity mismatch. Speed checkpoints along the route track the front, middle and rear. When the front slows or stops while the rear keeps walking, the rear pushes into the middle and the middle is pressed against the stationary front. That is the compression that becomes a crush. The response runs in three stages. Detect: cameras and speed checkpoints identify the abnormal cell or the abnormal deceleration. Relay: alerts reach a central monitoring point, giving the control room a ranked list of dangerous cells instead of a wall of video. Disseminate: a drone is sent to hover over the flagged pocket, carrying a directional guiding light that shows which way to move and a pulsed tone near 3 kHz, the frequency where human hearing is most sensitive, so it cuts through crowd noise at low volume without causing panic. Existing systems report a crush to a screen. This one speaks to the people inside it.