**4.2 Simulating the hazardous substance leakage by software ALOHA**

Our simulation of the emergency scenario took into account the formation of a crack on the surface of one of the containers causing a leakage of the whole volume of the ammonium hydroxide (63 m3) to the emergency tank (280 m3) during two minutes. Therefore we simulated the emergency scenario as the spill evaporation from the emergency tank (280 m3) on the basis of the defined atmospheric data.

However, it is necessary to say it was not possible to define the atmospheric data accurately as the emergency tank is located under the terrain level and this fact can affect the spreading of the gaseous ammonia. The surrounding buildings and terrain are not accurately defined in the simulation and it can also affect the spreading of the gaseous ammonia [30].


**Table 4.** *Input data.* *Risk Management in the Area of Major Industrial Accident Prevention in the EU… DOI: http://dx.doi.org/10.5772/intechopen.98406*

Based on the defined input data from the **Table 3** the software ALOHA graphically assessed the safe zones with a different concentration of the hazardous substance – see the **Figure 3**.

For us to understand the designations better, the following text describes the individual effects in the case of exposures to the hazardous substance to one of the zones.

ERPG 1 – Under this concentration the exposed persons can expect a low, insignificant and temporarily fugitive effect to their health within one hour or to perceive a clearly defined odour.

ERPG2 - Under this concentration the exposed persons can expect an irreversible effect to their health within one hour or less or any symptom that would reduce their ability to realise their personal protection.

ERPG 3 - Under this concentration the exposed persons can expect life-threatening effects to their health within one hour [3].

The abbreviation ppm means the amount of the volume parts of the given hazardous substance per million volume parts of the air.

Subsequently these graphical ALOHA outputs were transferred to the map material through the programme MARPLOT for the direction and reach of spreading the hazardous substance from the leakage source to be depicted. This depiction can be seen in the **Figure 4**.

The **Figure 4** shows the zone of the direct threat in the framework of which the persons can be exposed to the life-threatening effects can be found only in the operator's premises or it can partially hit the areas of the surrounding area. The next threat-zone covers several buildings with the services for the citizens. They are especially the bus stop, public road and staff quarters - here we can assume the occurrence of people. The last yellow zone covers only the uninhabited area where no people's occurrence is assumed. The **Table 5** shows the assumed distance of the reach of the threat-zones.

Our model example processed in the software ALOHA presents our attempt to show the risk of the leakage of ammonium hydroxide from the storaging premises in the company. Based on the assigned parameters we worked out a type scenario of leaking the toxic fumes of this hazardous substance. However, as it has been already mentioned, the software is not able to model certain parameters that would affect the spreading of the toxic fume – e.g. the terrain or the building layout.

#### **Figure 3.**

*A graphical depiction of the dangerous zones with the given concentration of the hazardous substance [30].*

**Figure 4.** *The reach of the toxic fumes in the map [30].*


#### **Table 5.**

*The distances of the threat zones.*

Certain safety systems in the company are to be taken into account, e.g. detecting the hazardous substance leakage, warning the employees in the case of the leakage and their subsequent immediate evacuation from the threatened surroundings, etc. Besides these facts there are also the emergency units that are able to affect the spreading process by their immediate response.

Based on the emergency scenario and the aforementioned facts which are not involved in the type scenario we can assume that the leaked toxic fume of the ammonium hydroxide should not exceed the company premises and to threaten the persons in the plant surroundings. We do not assume any impacts on the health of the persons and employees in the company due to their preparedness for such a scenario.

This type scenario was worked out for the needs of depicting the simulation possibilities in the software ALOHA.
