The Model for Effects with Toxic and flammable gases, in short, the MET, allows one, using the PocketPC version, to rapidly determine the critical distances for toxic substances for persons outdoors and in the protection of buildings.

The programme provides you with a decision-making aid that ensures simple and reliable operation and which asks you a question step by step in each case that you answer by choosing an input specification. There is a mass input dialogue at the end of this question-answer sequence. Here you determine the released mass and activate the 'Estimate danger distances' button. The programme then indicates the critical distances for persons outdoors, for persons inside buildings and the angle of dispersion.

A truck tank with 30'000 lb of cryogenic ammonia is torn apart during a collision. The entire contents are released. At the time of the accident at 1:35 pm, a wind of approx. 6 mph is blowing, the sky is clear.

Starting from the dialogue 'MET hazard diamond', the left button on the mask with the name 'MET' is activated. MET is started in the subsequent dialogue by confirming the 'START' switch:

Having pressed the 'START' switch, the first question asking you whether there is any mist directly in the area of diffusion from the toxic cloud.

There is no fog according to the description of the weather conditions, so our reply is 'No’:

The programme asks whether strong wind is present. We reply 'No':

In our case the sky is clear, so we choose 'No':

The time is during the day, so we activate the 'Daytime' button:

There is no wind that is blowing very gently, because according to the above description, the wind velocity is approx. 6 mph, so we choose the 'No' option:

There is no fire so we choose the ‘No’ option: 

Ammonia has been released as a cryogenic gas so we choose ‘Yes’:

We enter the released mass of ammonia into the programme and activate the 'estimate danger distances' button:

The programme estimates a critical distance of 2900 ft for persons indoors and 500 ft for persons inside a building. 

The distance specified from the point of release is equivalent to the distance at which 10% of the persons in a population who have negative health effects due to the released substance can still manage to react. 

Tour Step 4: Substance data