Table 4 Impact states for expected impacts to critical infrastructure as a function of tephra fall thickness. Modified and updated from Wilson et al. (2014)
From: Framework for developing volcanic fragility and vulnerability functions for critical infrastructure
| Â | Impact State | IS0 | IS1 | IS2 | IS3 |
|---|---|---|---|---|---|
| Â | Description | No damage | Cleaning required | Repair required | Replacement or financially expensive repair |
Electrical supply | Threshold (mm) | <3 | 3–10 | 10–100 | >100 |
Damage | No damage | Possible abrasion to some moving parts, infiltration of tephra into substation gravel. | Damage to exposed equipment especially those with moving parts, possible electrical line breakage. | Structural damage to some equipment at generation and transmission/distribution sites, irreparable damage to moving parts (e.g., hydro power turbines). | |
Disruption | No disruption | Temporary disruption to service caused by insulator flashover, cleaning and repair. | Widespread disruption to electrical supply with possible permanent disruption. | ||
Water supply network | Threshold (mm) | <1 | 1–20 | 20–100 | >100 |
Damage | No damage | Possible clogging of filters and some abrasion to moving components. | Damage to pumping equipment, other moving parts and infilling of tanks. | Collapse of reservoir roofs and infilling of open reservoirs and tanks. | |
Disruption | No disruption | Normal operation with increased frequency of filter cleaning and increased turbidity. | Contamination of water and increased treatment required. Possible water use restrictions. | Severe contamination of water supply and exhaustion of supply due to damage and/or increased demand. | |
Wastewater network | Threshold (mm) | <3 | 3–10 | 10–50 | >50 |
Damage | No damage | Possible minor abrasion to pumps, clogging of filters and possible interference with chemical treatment process. | Large amounts of sedimentation in network some causing blockages, some damage to treatment plant components and possible infilling of open tanks. | Widespread sedimentation throughout entire network causing some blockages, irreparable damage to pumps and extensive structural damage to treatment plant components. | |
Disruption | No disruption | Reduced capacity, operation with increased cleaning of filters. | Temporary disruption to service to unblock network and clean tanks possibly resulting in discharge of untreated sewage. | Long term to possible permanent disruption to service. Unable to treat wastewater. | |
Airport | Threshold (mm) | <1 | 1–30 | 30–150 | >150 |
Damage | No damage | Possible abrasion of runway, apron markings and paved surfaces as a result of clean-up operations. | Moderate abrasion of paved surfaces and landing lights. | Complete burial. | |
Disruption | Airport open | Airport closure, reduced visibility and traction. | Possible permanent closure. | ||
Road | Threshold (mm) | <1 | 1–100 | 100–250 | >250 |
Damage | No damage | Possible increased abrasion of road markings and paved surfaces. | Weak bridges may experience structural damage. | Complete burial, structural damage to some bridges. | |
Disruption | No disruption | Reduced visibility, loss of traction, covering of markings and possible road closure. | Roads impassable for some vehicles. | Roads impassable if tephra is unconsolidated, compacted tephra may be driven on by some vehicles. Likely road closures. | |
Rail | Threshold (mm) | <1 | 1–30 | 30–150 | >150 |
| Â | No damage | Possible abrasion and/or corrosion of railway tracks and signals, jamming of mechanical signals and contamination of track ballast. | Complete burial | ||
| Â | No disruption | Reduced visibility, signals and communications disrupted. | Possible loss of grip and derailing. | Impassable. | |
Critical components | Threshold (mm) | <1 | 1–10 | 10–50 | >50 |
Damage | No damage | No damage | Abrasion of moving parts and blockage of filters. | Extensive damage to most components. | |
Disruption | No disruption | Reduced function until cleaned | Reduced function and temporary shutdowns until cleaned | Uneconomic to repair, disruption to service until replaced. | |