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George A. Everding, AIA, CCS, CSI
Senior Member
Username: geverding

Post Number: 27
Registered: 11-2004
Posted on Thursday, March 31, 2005 - 10:11 am:   Edit PostDelete PostPrint Post

What was the reference standard that identified rated doors by letter designations (B-label) and when did it become obsolete in favor of hourly designations (1 1/2 hr.)?
William C. Pegues, FCSI, CCS
Senior Member
Username: wpegues

Post Number: 365
Registered: 10-2002
Posted on Thursday, March 31, 2005 - 12:22 pm:   Edit PostDelete PostPrint Post


I don't know where it originated, but I have seen the letter designations listed in many different other standards.

It has been around for a long time, I remember it from my early days in the 70s.

However, even then we were always correcting the door schedule and making the project architect's remove the letter designations and use the true hour/minute rating.

Reason why? B Label had 2 designations. There was a B 1-hour and a B 1-1/2 hour label. So why use that and its resultant potential for contractor confusion and just go straight to the hourly.

Even back in the 70s we were discouraging the letter designations. Nowdays, its pretty standard to not use them and see only the hour/minute designator. About the only time I ever see a letter designator used is on projects by interior designers.

Posted on Thursday, March 31, 2005 - 12:29 pm:   Edit PostDelete PostPrint Post

Door labels???
.... ugh, OK. How many would you like to buy?
Kenneth C. Crocco
Senior Member
Username: kcrocco

Post Number: 21
Registered: 04-2003
Posted on Tuesday, April 05, 2005 - 12:21 pm:   Edit PostDelete PostPrint Post

The designations, I believe, are from NFPA 80 Fire Doors and Fire Windows. The older designations of letters were used in previous issues of NFPA 80. The new standard lists ratings in terms of minutes: 20, 45, 60, 90,
David Axt, AIA, CCS, CSI
Senior Member
Username: david_axt

Post Number: 432
Registered: 03-2002
Posted on Thursday, April 07, 2005 - 12:59 pm:   Edit PostDelete PostPrint Post

The Steel Door Institute (SDI) used to designate doors with letters:

A - 3 hour door
B - 90 minute door
C - 45 minute door
D - Exterior 90 minute door

That system was abandoned in lieu of just calling out the minute rating of the door. As you can see there is no 60 minute door designation.

So basically you should not be specifying with the letter designations.
David Stutzman
Senior Member
Username: david_stutzman

Post Number: 39
Registered: 07-2002
Posted on Thursday, April 07, 2005 - 01:47 pm:   Edit PostDelete PostPrint Post

The letter designations come from NFPA 80. They designate the door location only, not the required rating. A-label doors are used in fire walls, B-label in vertical shafts, C-label in partitions, and D-label for exterior locations.

You can get a 90 minute B-label and a 60 minute B-label door. So using the lettered label designations was never a complete description of the fire rating requirement.
David Axt, AIA, CCS, CSI
Senior Member
Username: david_axt

Post Number: 435
Registered: 03-2002
Posted on Monday, April 11, 2005 - 05:33 pm:   Edit PostDelete PostPrint Post

I checked with my local steel door supplier and they still use the letter nomenclature to order doors. I guess old habits die hard.
John Bunzick, CCS, CCCA
Senior Member
Username: bunzick

Post Number: 348
Registered: 03-2002
Posted on Tuesday, April 12, 2005 - 08:47 am:   Edit PostDelete PostPrint Post

Yes, and steel door suppliers still use gauge to measure thickness.
Joseph Berchenko
Advanced Member
Username: josephberchenko

Post Number: 5
Registered: 08-2003
Posted on Wednesday, April 13, 2005 - 01:09 pm:   Edit PostDelete PostPrint Post

BTW. The letter "S" should appear on smoke door labels per the IBC. Additionally, some manufacturers have proposed using letters A through J on their labels to indicate product "Category."

As I understand it, these categories relate to edge condition and positive pressure testing for various door components. Category A indicates doors that do not require additional edge seals to meet positive pressure testing, usually because they have built-in intumescent seals. Category B doors require an attached edge seal to meet requirements. Other labels are for opening components other than doors: Category C is for frames; D is for door/frame assemblies; E is for hardware; F is for light kits; G for edge seals themselves; H for smoke and draft control gaskets; and J for other types of gaskets.

Some manufacturers have info on their web sites about category labels, but I have not yet found a good non-proprietary source on the subject.

Has anyone started seeing these category labels? Has anyone started specifying categories in their door schedules?
Tom Heineman RA, FCSI, SCIP
Senior Member
Username: tom_heineman

Post Number: 45
Registered: 06-2002
Posted on Thursday, April 14, 2005 - 09:19 am:   Edit PostDelete PostPrint Post

Do you know what the format is for adding A and B category designations?
Are these suffixed to the minute designation? Is there any delimiter: a hyphen? a space? no space?
My state is just publishing its newly adopted IBC code, so I will not be able to look up this requirement for a month or two.
Joseph Berchenko
Senior Member
Username: josephberchenko

Post Number: 6
Registered: 08-2003
Posted on Thursday, April 14, 2005 - 11:33 am:   Edit PostDelete PostPrint Post

I first learned of this at a presentation by David San Paolo with the Maiman Company. They have some additional info at the Maiman web site under http://www.maiman.com/download/pdf/Maiman_Bndr_Sec_10_Pos_Pressure.pdf. This includes a tech bulletin very similar to one on the WDMA website.

Neither the 2003 IBC (see 715.3.5.1) nor NFPA 80 discuss "Categories" as far as I can tell (Note, though, Appendix E of NFPA 80 answers original question about letter vs. time designation of ratings.)

Not sure without further research what the format is or who originated it, but I understand both UL and Warnok Hersey have a certain format they use for their labels that now includes Categories. Perhaps someone else can enlighten us.

I bring this issue up because it's possible to see "Category A" and "20 minute" on a label and be confused if you don't know that "Category" differs from "Fire Resistance Rating." This might have been what occasioned the original query for this thread.
Posted on Monday, June 20, 2005 - 06:44 pm:   Edit PostDelete PostPrint Post

I am looking for informtion on Thermal Break Down Frame usage, is anybody advise me where actually these frames can be use.

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