Hazard distance
If this leaks, how far does it reach?
Set what is leaking, how big the hole is and what the weather is doing. The map is a plan view of an ordinary site — a fence, a road, a football ground, housing, a school — drawn to scale in both directions, and the shape on it is the model’s own output rather than an illustration of one.
Life-threatening concentrations reach 120 m downwind.
- DiscomfortAEGL-1to 910 mNoticeable irritation. Reversible once the cloud passes.
- Escape impairedAEGL-2to 350 mSerious, lasting effects. People here may not be able to walk out.
- Life-threateningAEGL-3to 120 mAn hour in here is expected to kill.
Who is inside the boundary
- Site fence — escape impaired
- Public road — escape impaired
- Football ground — clear
- Workers' housing — discomfort
- School — clear
- Town — clear
- Heavier than air. Released cold and heavy, ammonia sinks and spreads along the ground instead of mixing upward. A Gaussian plume has no way to represent that: expect it to put the cloud too high, too thin and too far.
How this is worked outHide the method
A vapour release through a sharp-edged hole in a 8 bar a refrigeration plant, discharging 0.67 kg/s, carried downwind over open flat ground at 15 °C. Choked-orifice source term into a Pasquill–Gifford Gaussian plume with Briggs (1973) open-country coefficients; flammability limits from our hazardous-materials database, AEGL 60-minute thresholds from the published values. It is the same screening physics the platform runs first — and it is only in scope between 100 m and 10 km, on ground with nothing on it. Real sites have terrain, buildings and pipe racks, and those move the answer more than any slider here. That is the part the platform does. This panel is a demonstration, not a deliverable: do not use these figures for design, siting, emergency planning or a safety report.
Where this stops
The easy half of the question
A plume correlation assumes flat open ground and a source small enough to be a point. Real sites are neither. Put a bund wall, a pipe rack or a row of tanks in the way and the cloud does something a correlation has no way to represent: it channels down the gaps, it stalls in the lee of a building, it pools in a low corner and sits there.
Congestion also decides whether an ignition is a flash fire or an explosion, and that is not a distance calculation at all. The same release that this page draws as a smooth ellipse can, in a congested unit, produce an overpressure that reaches further than the cloud ever did.
That is the work the platform does: the same scenario on a computational grid that carries the geometry, with the validation record to say how far the answer can be trusted.
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