DOI: 10.3303/CET25119074 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Paper Received: 24 May 2025; Revised: 30 June 2025; Accepted: 9 October 2025 
Please cite this article as: Muratore A., Grillone G., Bellissimo M., Giannelli G., Nastasi V., 2025, Index Method for the Assessment of Natech 
Risk from Storms, Chemical Engineering Transactions, 119, 439-444  DOI:10.3303/CET25119074 
  

 CHEMICAL ENGINEERING TRANSACTIONS  
 

VOL. 119, 2025 

A publication of 

 

The Italian Association 
of Chemical Engineering 
Online at www.cetjournal.it 

Guest Editors: David Bogle, Flavio Manenti, Piero Salatino 
Copyright © 2025, AIDIC Servizi S.r.l. 
ISBN 979-12-81206-20-5; ISSN 2283-9216 

Index Method for the Assessment of Natech Risk from Storms 

Antonino Muratorea,*, Giovanni Grilloneb, Maurilio Bellissimob, Giuseppe Giannellia, 

Vincenzo Nastasib 

aInail, UOT Como, Via Petrarca 4 - 22100 Como, Italy 
bInail, UOT Palermo, Viale del Fante 58/D - 90146 Palermo, Italy 

a.muratore@inail.it  

Climate change has an impact on both urban and industrial environments. In the industrial environment, the 

plants that require the most attention are those that handle hazardous chemicals. 

In this work we consider the effects of meteorological climate changes such as storms, with their accompanying 

(Necci et al., 2022): 

• Heavy precipitation, which can lead to flash floods  

• Storm surges 

• Strong winds 

• Lightning 

Such effects can cause, in industrial plants with the presence of hazardous substances: fires, explosions, 

releases of hazardous substances into the environment which often lead to plant and production shutdowns for 

a long time. According to the recent approach of the IPCC (Intergovernmental Panel on Climate Change of the 

United Nations) the concept of risk associated with climate change is based on three fundamental components: 

hazard, exposure and vulnerability. There is a risk if in a certain place and at a certain time a vulnerable receptor 

is exposed to a source of danger of a climatic nature (IPCC, 2022). 

The aim of this work is to introduce, for the Italian production reality, a simplified index method for determining 

the level of natech risk from storms in industrial activities with presence of dangerous substances. The level of 

storm natech risk is identified through the index IRns which depends on: the storm hazard index IHs (function of 

lightning, floods, strong wind); the storm vulnerability index, IVs and the storm exposure index, IEs. After having 

calculated the level of risk natech from storms IRns it is possible to predict the main adaptation actions with the 

aim of increasing the resilience of the plant containing hazardous substances against storms. 

1. What are storms 

Storms are extreme weather events, characterized by a very low pressure area (depression), which are more 

intense the lower the pressure minimum. These are disturbances often associated with a cyclone. In the 

Mediterranean these events also bring very heavy rainfall, strong thunderstorms with violent gusts of wind, 

tornadoes or hail. A significant example is the storm called Vaia in October 2018, associated with a pressure 

minimum of 975 hPa, which caused winds so strong that they knocked down millions of trees in the Dolomites, 

and exceptional storm surges in Liguria with waves over 10 meters high. In 2015 EUMETNET (Network of 

European Meteorological Services), a European intergovernmental organization whose objective is to ensure 

and facilitate cooperation between the national meteorological and hydrological services of Europe, established 

the “Storm naming” project, to name the most intense storms as already happens in the United States of America 

for hurricanes. For this program, Europe has been divided into several groups of countries (Fig. 1) (Canessa, 

2021). Italy belongs to the Central Mediterranean group, which includes Slovenia, Croatia, North Macedonia, 

Montenegro and Malta. Since 28 September 2021, the Italian Air Force Meteorological Service has been naming 

the most intense storms affecting Italy, in coordination with the countries of the “Central Mediterranean Group”, 

consisting of ARSO METEO (Slovenia), DHMZ (Croatia), YXMP (North Macedonia), Malta Meteorological Office 

(Malta) and IHMS (Montenegro). 

 

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Figure 1: Storm naming project 

2. Impact of storms on industries with major accident hazards 

Industrial activities are not normally perceived as sectors vulnerable to climate change. In particular, the increase 

in frequency and intensity of extreme weather events such as storms significantly impact industries and plants 

that contain dangerous chemical substances, causing Natech (Natural Hazard Triggering Technological 

Disaster) events that involve fires, explosions and releases into the environment. All this leads to involving not 

only the workers of plants but also the citizens who live in their vicinity. The authors introduce an index method 

for the Italian production reality to determine the level of natech risk induced by storms in industrial activities 

with the presence of dangerous chemical substances that fall within the scope of the European Directive 

2014/18/EU (Seveso Directive). According to the recent approach of the IPCC (Intergovernmental Panel on 

Climate Change of the United Nations, 2022) in general the concept of meteorological risk from storms 

associated with climate change is based on three fundamental components: hazard, exposure and vulnerability. 

We therefore speak of risk if in a certain place and at a certain time a vulnerable receptor, that is, one that can 

suffer the consequences triggered by the danger, is exposed to a source of danger. In this work we consider 

the effects of meteorological climate changes such as storms, with their accompanying (Necci et al., 2022): a) 

Heavy precipitation, which can lead to floods; b) Storm surges; c) Strong winds; d) Lightning. The level of storm 

natech risk is identified through the index “IRns” which depends on: the storm hazard index “IHs” (function of 

lightning, flash floods, strong wind); the storm vulnerability index “IVs” and the storm exposure index “IEs”:  IRns = 

f (IHs, IVs, IEs). Since determining the function “f” is quite complex in terms of time and resources, the simplified 

index method proposed by the authors is: 

 

IRns = IHs * IVs * IEs                   (1) 

To determine the level of natech risk from storms “IRns” it is necessary to determine the values of IHs, IVs , IEs.   

After having calculated the level of risk natech from storms IRns it is possible to predict the main adaptation 

actions with the aim of increasing the resilience of the plant containing hazardous substances against storms. 

This method allows to perform a preliminary assessment of the Natech risk from Storm, in order to identify the 

critical elements of a plant. Any further investigations, in cases of non-linear interactions between the three 

indices, can be performed subsequently.  

3. How to determine the storm hazard index, IHs  

The storm hazard index “IHs” depends on weather events: a) Heavy precipitation, which can lead to flash floods; 

b) Storm surges; c) Strong winds, d) Lightning. This index “IHs” is given an increasing value between 1 and 4. 

Therefore, considering an equal contribution from the previously reported weather events, we obtain: 

 

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IHs = (IHsp + IHsw + IHsl) / 3                 (2) 

Where: A) “IHsp” is an index with a value from 1 to 4, which depends on heavy precipitation (in the presence of 

flash floods or storm surges, one unit is added to the value obtained); B) “IHsw” is an index with a value from 1 

to 4, which depends on strong winds; C) “IHsl” is an index with a value from 1 to 4, which depends on the density 

of lightning to the ground (average number of lightning strikes per km2 per year; value detectable from lightning 

location networks located throughout the territory). 

3.1 How to determine the precipitation storm hazard index, IHsp  

According to the recent report n 42/2024, presented by SNPA (Italy, National System for the Protection of the 

Environment) concerning the climate in Italy in 2023, regarding precipitation, Figs. 2 and 3 are shown below 

(SNPA Report, 2024). 

 

 
Figure 2. Anomaly of the cumulative annual 

precipitation 2023, expressed in mm, compared 

to the normal value 1991-2020. 

 
Figure 3. Maximum daily precipitation 2023. 

 

Using Fig. 3 where the maximum daily precipitation in mm is reported for Italy, it is possible to determine the 

precipitation storm hazard index, IHsp. To calculate the value of this index, the authors, based on their experience, 

propose the following table 1: 

Table 1. Relationship between daily maximum precipitation in mm and precipitation storm hazard index, IHsP. 

Maximum daily precipitation in mm IHsp 

< 50 1 

≥ 50 < 100 2 

≥ 100 < 150 3 

≥ 150 4 

Heavy rainfall impacts the safety of equipment containing hazardous substances, whether they work under 

pressure (vessels, reactors, etc.) or not under pressure (fuel storage tanks, etc.). It is necessary to identify and 

analyse equipment in order to define which are the critical elements of certain industrial plants (Muratore et al., 

2022). Finally, it is necessary to define the vulnerability of critical elements that are at the basis of incidental 

events such as fires, explosions and releases into the environment (Muratore et al., 2024). 

3.2 How to determine the wind storm hazard index, IHsw  

To determine the index relating to strong wind, reference is made to the Italian Wind Atlas. It is a very useful 

resource resulting from the collaboration between ERSE (ENEA-Electrical System Research) and the University 

of Genoa, and can be easily viewed in interactive form. For Italy is reported below: the ground measurement 

stations of the wind atlas anemological database (Fig. 4) and the map of the average wind speed (Fig. 5),  

 

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Figure 4. The ground measurement stations of 

the wind database of the Wind Atlas. 

 
Figure 5. Map of the average wind speed at 25 

meters above sea level and up to 40 km from the 

coast. (source: ERSE/University of Genoa). 

 

Where ERSE means ENEA-Electrical System Research and ENEA means Italian National Agency for New 

Technologies, Energy and Sustainable Economic Development. 

For a first preliminary evaluation of the wind index IHsw, it can be related to the average wind speed found in 

figure 5. To calculate the value of this index, the authors, based on their experience, propose the following table 

2: 

Table 2. Relationship between wind speed and the wind storm hazard index, IHsw. 

Wind speed [m/s] IHsw 

< 3 1 

≥ 3 < 5 2 

≥ 5 < 7 3 

≥ 7 4 

3.3 How to determine the lightning storm hazard index, IHsl  

Among the countries in the world that receive the most lightning strikes in absolute terms are Brazil and the 

United States, while Italy is among the European countries that receive the most lightning strikes per square 

kilometres on average. Today in Italy it is possible to determine the point of impact of a lightning strike with a 

precision of about 500 meters thanks to the SIRF (Italian Lightning Detection System) lightning detection 

system. For the analysis of the chronology of lightning events, you can refer to the CEI ProDisTM online 

application which is structured on data acquired from the SIRF monitoring network. This application provides 

information (indicated by the symbol Ng) that represents the average number of lightning strikes to the ground 

per year per Km2 calculated using a grid with square cells with sides equal to 5 Km, based on lightning data 

collected in over ten years of observations throughout Italy. In relation to this, the manufacturer is able to 

determine the value of Ng for his establishment. The higher the Ng value, the greater the probability that lightning 

strikes the industrial site being assessed.  

Using CEI ProDisTM online application it is possible to determine the lightning storm hazard index, IHsl. To 

calculate the value of this index, the authors, based on their experience, propose the following table 3: 

Table 3. Relationship between Ng and lightning storm hazard index, IHsl. 

Ng IHsl 

< 1 1 

≥ 1 < 2.5 2 

≥ 2.5 < 4 3 

≥ 4 4 

4. How to determine the storm vulnerability index, IVs 

In industrial plants it is important to identify the vulnerability of critical equipment that is the basis for triggering 

natech events from storms. The risk analysis methodology used by the Seveso industry often resulted in 

scenarios related to Natech (Castro Rodriguez et al., 2023). Among the equipment with greater criticality in this 

work are considered those containing hazardous substances present in the process and storage industry: 

pressurized equipment, built according to Directive 2014/68/EU (PED – Pressure Equipment Directive) 

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(spheres, columns, reactors, exchangers, tanks, ovens), atmospheric storage tanks (fixed or floating roof) and 

piping systems containing or conveying hazardous substances (pressurized or not). In Table 4 we relate the 

type of equipment containing hazardous substances with the storm vulnerability index "IVs". The latter is 

determined in a range from 1 to 4 in the light of the authors' experience in the field. The values must take into 

account the maintenance status of said critical equipment.  

Table 4. Relationship between equipment containing hazardous substances and storm vulnerability index, IVs 

Equipment type Filling level Construction features IVs 

Floating Roof Tanks ≥50% / < 50%     4 / 3 

Fixed Roof Tank ≥50 % / < 50%   3 / 2 

Pressure equipment (Spheres, 

columns, reactors, ovens, etc.) 
  before PED / according to 

PED  
3 / 2 

Pipes under pressure  

Pipes not under pressure 

 before PED / according to 

PED 
2 /1 

1 

5. How to determine the storm exposure index, IEs 

Exposure means the extent and severity of damage to receptors potentially affected by the effects of incidental 

events caused by storms (workers, population, environment, assets, infrastructures). As regards industrial 

structures (intended as buildings, parts of plants, equipment, pipelines, etc. or power lines connecting industrial 

plants). The analysis of Natech incidents triggered by storms can cause loss of containment, with the possibility 

of fire and/or explosion, if they contain combustible, flammable or explosive substances; due to alterations in 

processes caused by interruptions in electrical power and voltage drops and impacts on electrical and electronic 

control and safety systems, plants and devices. The consequences of damage and failures can extend to the 

surroundings, affecting other parts of the plant and in certain cases also affecting the surrounding environment 

(Domino Effects). In relation to the above, the authors propose to give the exposure index IEs from storms the 

following values shown in table 5: 

Table 5. Relationship between storm exposure type and storm exposure index, IEs 

Storm exposure type IEs 

Only possible impacts that lead to the failure of equipment 

without loss of content of hazardous substances 

1 

Possible impacts in the vicinity of the affected unit. There 

is no possibility of a domino effect (for example, a tank 

adjacent to other tanks) 

2 

Possible impacts that may involve the entire plant 3 

Possible impacts that may involve the outside of the plant 

with the possibility of a domino effect 

4 

6. Level of acceptability of natech risk from storms 

Once the three factors that influence the level of natech risk from storms have been identified through the 

respective IHs, IVs and IEs indices, it is possible to determine the natech risk index from storms IRns as per report 

(1) of paragraph 2 of this article. For IRns values up to 8, the risk is acceptable but appropriate prevention and 

protection actions must be planned over time. For values of IRns higher than 8 and lower than 32, the natech risk 

from storms must provide for urgent prevention and/or protection interventions such as to make it acceptable. 

For values of IRns greater than 32, the natech risk from storms is not acceptable. 

7. Interventions in order to reduce the vulnerability of critical elements of natech risk from 
storms 

In the case of newly built industrial plants, it is important to identify the installation site. In this way, you are able 

to manage the three factors that influence natech risk from storms: IHs, IVs and IEs, bringing them to the lowest 

possible values. In the case of existing establishments, for the purposes of managing the natech risk from 

storms, only one factor can be acted upon, which is vulnerability IVs, while little can be done about the other two 

factors IHs and IEs which depend on the location of the industrial site and the neighboring urban planning. The 

following are some (non-exhaustive) examples of how to reduce the vulnerability of Critical Industrial Plants 

from storms: 

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• Technical interventions: In this regard, place generators, pumps and control rooms above the hydrometric 

level that can normally be found from the time series that affect the plant. Provide for the installation of 

devices to ensure electrical continuity or to limit overvoltages, adopting protective measures to ensure that 

the path of lightning strikes is kept away from flammable and explosive substances, through preferential 

low-impedance routes, taking advantage of the characteristic of metals to be good conductors. Provide: a) 

appropriate anchoring of equipment and systems taking into account the wind speed of the site; b) special 

walls and diaphragms in order to prevent water from entering the production site from outside; c) special 

tanks for the collection of water coming from the yards and basins of the plant; etc. 

• Maintenance, control and verification interventions: Appropriate maintenance and inspection of the 

protection systems from lightning risks must be provided, which includes the carrying out of tests and 

electrical continuity measurements; in fact, systems against atmospheric discharges tend to lose their 

effectiveness over time due to corrosion and damage due to environmental conditions, mechanical shocks 

and lightning strikes. Systematically clean any ducts that are located near the production site. 

• Organisational interventions: Activate suitable weather alert systems. In this regard, prepare suitable 

procedures to be activated in time in order to make people and plants safe. 

The above-mentioned interventions improve the resilience of individual industrial activities, both in terms of 

vulnerability of critical elements and in terms of exposure for settlements near the establishment. 

8. Conclusions 

The increase in the frequency and intensity of extreme weather events such as storms have a significant impact 

on industries and plants that contain hazardous chemicals, with the possibility of causing Natech events that 

involve fires, explosions and releases into the environment. All this leads to the involvement not only of the 

workers of these plants but also of the citizens who live in the vicinity of them. In the light of what has been 

highlighted in this article, a preliminary index method is introduced for the Italian production reality to determine 

the level of natech risk induced by storms in industrial activities. The purpose of this work is to give 

managers/employers indications regarding the adaptation to storms that are often accompanied by heavy 

precipitation, which can lead to flash floods, storm surges, strong wind and lightning. The proposed method can 

be applied to all geographical areas, provided that it is possible to determine the storm hazard index, IHs for the 

single area. This is possible if are available: a) Maximum daily precipitation in mm, b) Wind speed in m/s, c) The 

average number of lightning strikes to the ground per year per Km2, for each single area. The other two indices 

storm vulnerability index, IVs and storm exposure index, IEs are not influenced by the geographical area. 

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	Index Method for the Assessment of Natech Risk from Storms