Buildings | ND | No structural damage to buildings; possible infiltration and internal contamination and corrosion of metallic components; roofing materials may be abraded or damaged by human actions during ash removal | In rare instances, non-engineered and long span roofs may be vulnerable to damage, particularly when ash falls wet or is subsequently wetted; non-structural elements such as gutters and overhangs may suffer damage; some infiltration of dry ash into interiors | Structural damage; partial to complete collapse of weak (timber, corrugated metal) roofs | Structural damage; partial to complete collapse of concrete roofs | ||
Power system / telecommunication | ND | Temporary disruption of power system particularly with wet ash (e.g. flashovers); possible communication signal attenuation (e.g. radio); uninsulated lines may flashover. | Damage to telecommunication components and power cables through flashover; abrasion and or corrosion; failure of power generating plant (depending on system type and design); abrasion, clogging and flash-over causing disruption and/or damage to some electrical and mechanical equipment at substations | Damage to communication dishes and microwave towers due to excess of ash loading; structural damage to electrical distribution lines and support structures | Damage to communication dishes and microwave towers due to excess ash loading; permanent disruption and structural damage of power system | ||
*Transport system | Minor skid resistance reduction possible and covering of markings | Skid resistance reduction likely and covering of markings; poor visibility; windscreen abrasion | Minor skid resistance reduction possible and covering of markings, poor visibility, windscreen abrasion | Minor skid resistance reduction possible and covering of markings; poor visibility; clogging of roadside drains and ditches; increased wear of engine and brakes and windscreen abrasion | Impassable for some vehicles and covering of markings; poor visibility. Dry, windy conditions exacerbate remobilisation and drifting. | ||
Hazard score | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
Tephra load (kg/m2) / thickness (cm) | 0.1–1 (0.01–0.1) | 1–5 (0.1–0.5) | 5–10 (0.5–1) | 10–100 (1–10) | 100–300 (10–30) | 300–500 (30–50) | > 500 (> 50) |