Lift Shaft Pressurisation

[Stormxtc]

Hi everyone,

Just a quick question on lift shaft pressurisation during fire mode.

We need to pressurise a lift shaft to between 20 - 50Pa only when there is a fire (as per Australian Standard 1668). However, I need to know the quantity of air that is required. How much air do I pump into the lift shaft when there is a fire?

I know that the US is probably slightly different but it may still help to point me in the right direction.

Thanks,

StormXTC

 

[ad77]

i have just done a quick search of the BCA and can not find any requirement for a lift shaft pressurisation system.

why are you designing a system that is not required by the building code? just because it is described in AS 1668.2 does not mean it is required in your building.

if the system is required get hold of texts by klote & milke(US) and butcher & parnell(UK). they give guidance on shaft/construction leakages etc and calculation proceduers that could assist in your design.

 

[Stormxtc]

Lift shaft pressurisation was one of the cheaper options presented by the fire engineer. He referenced Table E2.2a of the BCA and of course AS1668.1.

The other alternative is to install a smoke curtain on the elevator door on just one of the levels. Sounds easy until you try to contact companies who actually sell the damn things.

Of course stair pressurisation was the third alternative and the most expensive one.

Unfortunately, we do not have any of the books you suggested, however, I did find enough info in ASHRAE to calculate the required air flow (1800 l/s [about 240 l/s per elevator door] @ 30 Pa).

Thanks for the help,

StormXtc

 

[ChasBean1]

Stormxtc,

It looks like you found the same source I have (ASHRAE 2003 Applications Ch. 52). They say leakage is typically 0.55-0.70 ft^2 per elevator door. Not sure if you noticed also but elevator hoistway walls with "average" tightness have a leakage area to wall area ratio of 0.84 x 10^-3 (excluding doors).

Figure your total leakage from doors and the hoistway walls and use:

Q = 2610 A dP^.5

Q is airflow in cfm
A is total crack area in ft^2
dP is the pressure above ambient to be maintained in inches of water (at 30 Pa, 0.12 in. w.c.)

Sorry about the English units. ASHRAE still uses them and unfortunately I still think in those units.

Vr, CB

 

[ad77]

had another look at the BCA table e2.2a still can't find reference to lift shaft pressurisation.

must be a alternative solution based on a fire engineered design and not a prescriptive BCA deemed to satisfy design.

it sounds like an interesting left field solution by the fire safety engineer.

other things to consider;

does the lift operate during the fire mode?(some projects are currently utilising the lifts for emergency evacuation)

how will the lift movement impact on the pressuriation system?

relief air paths for the pressuriation system etc etc

let me know how it all ends up - by posting to this thread.

 

[Stormxtc]

ChasBean1,

I think we have indeed come across the same info in ASHRAE but mine is in SI units...bout time you guys upgraded to SI as well...

Anthonyd,

Yes I think it may be an engineered solution suitable for our project only. The alternative was to use smoke curtains in front of elevator doors during fire mode to prevent the spread of smoke to other levels.

The lift will have to be assumed to operate (although it should not) during fire mode. The reason is that disabled people need to use the elevator to quickly evacuate the building.

The pressurisation system will be sized to according to above mentioned flow and between 20-50Pa pressure. Anything more will effect the opperation of elevator doors and could also effect the overall air balance of the building. Our system is 30Pa and 1800l/s.

Relief air paths are your lift door gaps. The amount of air supplied into the shaft is equal to the amount of air that is lost through the lift door gaps. Hence it should not effect the operation of the lift during fire mode. At least I hope not!

The fan will also need a dimmer switch to allow for exact balancing of the fan to the pressure and flow required.

StormXTC

 

[remp]

anthonyd

I dont think the reference to lift shaft pressurisation is in the BCA, however I am almost sure its in a table at the back of AS1668.1 in the appendix. It gives you different options for buildings requiring smoke hazard management, and one of those options is lift shaft pressurisation

Regards

billyq

 

[ercanbaser]

BELOW TEXT IS FROM "NFPA 92A -1996 EDITION" IT MAY BE HELPFUL FOR THE DISCUSSION.


"2-4 Elevator Smoke Control.
2-4.1
Elevator hoistways have proved to be a readily available conduit for movement of smoke throughout buildings in past fires. This is because the elevator doors have not been tightfitting and elevator hoistways have been provided with openings in their tops. The building stack effect has provided the driving force that has readily moved smoke into and out of the loosely constructed elevator hoistways. Several methods of correcting this problem have been proposed and investigated. These include:
(a) Exhaust of the fire floor,
(b) Pressurization of elevator lobbies,
(c) Construction of smoketight elevator lobbies,
(d) Pressurization of the elevator hoistway, and
(e)* Closing elevator doors after automatic recall.
2-4.2
These methods have been employed either singly or in combination. However, their application to a particular project, including the effect of any vents in the elevator hoistway, should be closely evaluated. The open vent at the top of the elevator hoistway may have an undesirable effect on elevator smoke-control systems.
2-4.3
Fires have shown the tendency of smoke to migrate into elevator hoistways. Therefore, the use of elevators for egress purposes has not been favored. Research is currently under way to determine the feasibility of maintaining elevator hoistways free of smoke during fires."
...


Ercan

 

[Stormxtc]

Thanks Ercan,

StormXtc

 

[ad77]

billyq,

i am aware the appendix in AS1688 refering to lift shaft pressurisation.

my point being is that a BCA 'deemed to satisfy' solution does not reference lift shaft pressurisation. the BCA 'deemed to satisfy' solutions refers to shutdown, zone pressurisation and stairwell pressurisation for various class, size and height of buildings.

if a lift pressuriastion system is proposed further justification is required and documentary evidence to support the 'alternative solution' is required.

it appears that the solution proposed is an 'alternative solution' ie. performance based fire engineered solution. refer BCA section A 0.3 to A 0.9.

hope this clears up my position.

 

[paulkeating]

The need for lift shaft pressurisation is NOT directly from the simple fact that AS.1668 mentions it (after all, 1668 mentions shutdown system - chapter 6 - but BCA part E2.2 references chapters 5 and 7 but skips 6). However, there is a clause later in BCA (can't remember the number) where it says that the designer must not limit himself (or herself - sorry to those contradictory genders reading this ...) to the items listed in BCA. So, in that light, the BCA DOES actually tell you that you must look at your specific case and determine yourself if the BCA is adequate ....

(A big ask I know, but then again the BCA was probably written by 1 engineer with his 55 lawyer mates ....)

Hence the IMPLICIT requirement to "go beyond" table E2.2 and to assess the offerings and suggestions in the secondary documents ie in the referenced standards, henc elift shaft pressurisation.

(Similarly, look at the need for lift shaft RELIEF ... para 11.3, or something. NOT the same thing as pressurisation so read the language closely ....)

I've written to Standards asking them to clarify their call for lift shaft pressurisation.. _ I think their is confusion in that lift shaft pressurisation is NOT needed when you ALSO have a zone system - I'll let you know what they say.