Observations on Draft Stops / Water Curtains

Questions about Georgia Codes and Standards

Observations on Draft Stops / Water Curtains

Postby Blackstone on Wed Dec 10, 2008 2:43 pm

Observation #1: Intent?

120-3-3-.04(6)(b)(1) revised the following:
Add an Annex A. to to read as follows:
“A. It is the intent of this section to apply the requirement for draft stops and closely spaced sprinklers to openings in fire rated floor / ceiling assemblies. It is not the intent of this section to require draft stops and closely spaced sprinklers to the perimeter around mezzanines, raised platforms, lofts or other places where stairs or escalators ascend to a floor or landing that is open to the space below.

However, this appears to contradict NFPA in the following email:

-----Original Message-----
Sent: Monday, November 17, 2003 9:15 AM
To: Jaimie Blackstone
Subject: RE: NFPA 13 (2002), Section 8.14.4


Since you reference the 2002 edition, I have used that edition of NFPA 13 in preparing this response.

The direct purpose for vertical opening protection is not the same with regard to NFPA 13 and NFPA 101. With regard to adequately designing a fire sprinkler system, smaller vertical openings tend to create a 'chimney' condition more so than larger openings. Under this condition, the concern is that heat from a fire on a lower level will set off sprinklers on the
non-fire floors above, whose discharge cannot impact fire control. Because NFPA 13 requires the water supply for the fire sprinkler system to be determined based on a single level operating, this would overwhelm the water supply and could render the sprinkler discharge on the fire level useless.
Therefore, NFPA 13 requires a draft stop with closely spaced sprinklers for smaller vertical openings to prevent this problem. The 'chimney' effect is not considered a problem with larger openings because there are more upper level sprinklers available that can discharge to the lower level. My understanding is that the general concern with atriums from a life
safety standpoint (NFPA 101), is the quick travel of toxic gases (smoke) from a fire to multiple levels of the building, which is not a direct concern in NFPA 13.

With that in mind, the following responses are in the same order as the questions asked in your email below.

1. If the two openings are sufficiently separated such that they cannot be considered the same opening, then the smaller opening must have draft stops with closely spaced sprinklers even if the larger opening is not required to have such features. The problem of the 'chimney' effect still remains in that configuration for the smaller opening.

2. The requirements of Section 8.14.4 apply to any vertical opening between levels, so my understanding is that it would apply to mezzanines where an interior located opening and the major mezzanine opening are sufficiently separated such that they cannot be considered as the same opening.

Please note there was no mention of limiting this section to fire rated assemblies... and no exceptions - if it is a hole in the floor, this section applies unless it is a large hole as noted in the exception to this section
Observation #2: Justification?

120-3-3-.04(6)(b)(2) revised the following:
Renumber existing to and add a new to read as follows:
“ Draft stops required by Section shall not be required in Light and Ordinary Hazard Occupancies utilizing quick response sprinklers throughout.”

This section only eliminates the draft stops, not the closely spaced sprinklers that incidently would still be required, and which would be useless without something to collect heat...
Observation #3: From NFPA 13 (2007)

8.15.4* Vertical Openings.* General. Unless the requirements of are met, where moving stairways, staircases, or similar floor openings are unenclosed and where sprinkler protection is serving as the alternative to enclosure of the vertical opening, the floor openings involved shall be protected by closely spaced sprinklers in combination with draft stops in accordance with and Draft Stops. Draft stops shall meet all of the following:

(1) The draft stops shall be located immediately adjacent to the opening.

(2) The draft stops shall be at least 18 in. (457 mm) deep.

(3) The draft stops shall be of noncombustible or limited-combustible material that will stay in place before and during sprinkler operation. Sprinklers. Sprinklers shall be spaced not more than 6 ft (1.8 m) apart and placed 6 in. to 12 in. (152 mm to 305 mm) from the draft stop on the side away from the opening. Where sprinklers are closer than 6 ft (1.8 m), cross baffles shall be provided in accordance with Large Openings. Closely spaced sprinklers and draft stops are not required around large openings such as those found in shopping malls, atrium buildings, and similar structures where all adjoining levels and spaces are protected by automatic sprinklers in accordance with this standard and where the openings have all horizontal dimensions between opposite edges of 20 ft (6 m) or greater and an area of 1000 ft2 (93 m2) or greater.

And the appendix goes on to say:

A. It is the intent of this section to require closely spaced sprinklers and draft stops to openings where protection or enclosure is required by building and life safety codes.

Apparently NFPA's intent has not changed even in the 2007 edition.... no exceptions (other than as noted in the code for large openings), no limitations on rated floors, no elimination of the draft stop portion of the requirement where QR sprinklers are used, etc.

My understanding is that the reason the sprinklers are permitted to be omitted for the large opening is because they are less effective at protecting these larger openings, but the sprinklers/draft stop can provide valuable protection to prevent the spread of fire to the upper (or lower) level when used for the smaller/narrower openings.
We find consulations, we learn tricks with which we deceive ourselves, but the essential thing - the way - we do not find. Listen to the river.

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