What in the world is this signal?

[SilverThunder710YT]

I've been looking around YouTube at international sirens, and came across Severnside, UK's siren system, made of a dozen Federal Signal Mod 5020s and DSA6s and operated by a nearby industrial facility. I expected the sirens to have relatively normal signals, but their warning signal made me question if it was even real (which it is). Their all clear signal is just steady tone (which I expected.)

https://www.youtube.com/watch?v=OGUuKEXp_RE
https://www.youtube.com/watch?v=vei8lBeSozM

The sirens do two cycles of five whoops, then a normal windup, then eight pulse blasts. The signal is essentially just the "shelter in-place" sound but why not use a simpler signal like wail or hi-lo tone? Is there a specific reason why the signal is like this or is it just how the industrial company wanted it?

[duckwaddledup]

I believe it's slow whoop at first, but I don't know what the tone is. Could be custom though.

[Digisirran]

I've been looking around YouTube at international sirens, and came across Severnside, UK's siren system, made of a dozen Federal Signal Mod 5020s and DSA6s and operated by a nearby industrial facility. I expected the sirens to have relatively normal signals, but their warning signal made me question if it was even real (which it is). Their all clear signal is just steady tone (which I expected.)

https://www.youtube.com/watch?v=OGUuKEXp_RE
https://www.youtube.com/watch?v=vei8lBeSozM

The sirens do two cycles of five whoops, then a normal windup, then eight pulse blasts. The signal is essentially just the "shelter in-place" sound but why not use a simpler signal like wail or hi-lo tone? Is there a specific reason why the signal is like this or is it just how the industrial company wanted it?

Perhaps to distinguish from the other tones, not that they use the others apart from All Clear. But Wail or Hi-lo could potentially be confused for an emergency vehicle siren. That's just a theory as to another reason why.

The sirens cover not just one company but rather a few. Severnside have 5 higher tier and 3 lower tier companies; with Esso, Exolum, Flogas, Valero Energy and Yara UK Ltd. The remaining three being a treatment plant, a warehouse for distributing and storing fuel and a warehouse designed to store fertilisers.

There are 12 sirens in total to cover the potential risk areas if any disaster was to happen in one or more plants and warehouses.

AFAIK, the sirens aren't directly handled by the facilities but the Avon and Somerset Police. If a disaster or crisis at any of the plants occur, they get the notification to sound the sirens.

If it catches people's attention about a hazard on the way, then it works as intended. Hope this helps.