Why secure a loft trapdoor in a storm?

Why secure a loft trapdoor in a storm? And what's the roof pitch to do with anything?
"Close and secure loft trapdoors with bolts, particularly if roof pitch is less than 30°" https://www.metoffice.gov.uk/weather/warnings-and-advice/seasonal-advice/your-home/stay-safe-in-a-storm

On 07/01/2020 20:01, Commander Kinsey wrote:
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Bernouilli.

I don't know their reasons, but mine used to come open during high winds dumping tons of old muck and dust onto my landing. Its now held shut with duct tape. No nasty whining noises or rattles either. The roof on this property is open ie it can bee seen there are gaps under the tiles, so one assumes if that hole was through to the house and a really spectacular wind came it could blow many tiles off the roof. Brian

Ah, you mean one of those strange ones that opens downwards? Mine lifts up, a much more sensible arrangement. It simply cannot open itself, it's too heavy.
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