Fire regulations - viable escape route

[HappyTimes1981]

Hi - first time poster. Does anyone have any knowledge or advice on the below.

Our flat has the kitchen is on the mezzanine floor and one of the bedrooms comes off it. The flat is on the ground floor so the window from the bedroom is under 4.5 meter from the ground below. From my digging around- it seems that as long as the window has an opening of at least 0.33m and 0.45m, it's a viable escape route. Is that usually sufficient?

It's a Victorian School conversion done in 1981. The flat originally had 2 staircases in it - the second one came directly down from the landing area outside the upper bedroom door (there's an inner balcony as well that looks down into the hall) but it took up a ton of space, my partner had it removed. Been happy here for 8 years but now thinking of selling and want to be prepared for the worst if this comes up as an issue during the survey. Been reading into options like mist sprinklers - which are only a couple of grand, so it's not the end of the world if one needs to be installed.

Will eventually get some expert advice but wanted to gather a bit of insight first

Thanks x

Does the bedroom on the mezzanine have another escape route or a place of relative safety where someone can shelter pending emergency services? If not then is the kitchen enclosed or would someone have to travel past kitchen (most likely ignition source) to evacuate? If it's open plan this would be a concern. Not sure about size of escape aperture but distance to travel is also important.

Thanks for posting - The kitchen isn't enclosed, the mezzanine is all open plan. From the bedroom door, the kitchen is open the right and the staircase on the left of the door is 4 meters away. Technically they would be passing the kitchen. Shelter - not really, it's either out the window, past the kitchen or lowering yourself down into the hall from the landing right outside then bedroom door. :-/

We've had a similar issue with work based accommodation - our fire safety team insisted on a misting system over the hob which would suppress any fire. It's called ultra guard. Not sure what domestic fire regs are for older buildings but the second staircase was probably there for escape from that bedroom (unless it also took you past the kitchen) in which case you'd still need a suppression system. You could put a CO2 and a fire blanket on the kitchen and always always check your smoke alarm batteries and ensure you don't have too many smaller appliances (toasters, kettles, fryers) etc. Since we've had this issue I've looked at fire escape routes on a whole new light - it's not the likelihood of it occurring it's the reality of the damage that would happen very quickly if there was one.

Yeh, it reckon the second staircase was absolutely there for fire regs. It's still up for debate whether it was necessary on the ground floor due to being able to get out the window. They may have just be treating all the flats with the same design. I'm definitely thinking the misting system is a good option - and hopefully that won't be seen as a problem for the building board as this flat is on the ground floor and poses no flooding risk - might be different if there where flats below. I'll get my ducks in order with quotes and approvals etc and if it comes up in the survey, at least I'll be ready to act on it and know the costs.
You've been a great help!