This is known as a pyroclastic flow, or surge if the flow is dilute and turbulent. The flow direction may be topographically controlled. Pyroclastic flows and surges represent the most destructive manifestations of volcanic activity. People caught in the direct path of a flow or surge are most unlikely to survive. Those who are lucky enough to survive will receive severe injuries.
Buildings offer some protection at marginal areas of flows and surges but they are often destroyed.
The best protection is to evacuate prior to the event. The distance they travel depends on the viscosity of the lava, output rates, volume erupted, steepness of the slope, topography and obstructions in the flow path. Andesite flows are more viscous and rarely travel more than 5 kilometres. Dacite and rhyolite lavas have high viscosity and typically form short, thick flows or domes. Lava flows will seldom threaten human life because of their slow rate of movement.