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9/11 See other 9/11 Articles Title: WTC Tower Stairways Violated Building Codes The Building Codes required FOUR stairways, NOT THREE. The Building Codes required that the stairways be "as far apart as practicable." They were not. http://wtc.nist.gov/NISTNCSTAR1CollapseofTowers.pdf NIST NCSTAR 1, WTC Investigation Section 5, The Design and Construction of the Towers pp. 57/107 - 59/109 [SIDEBAR: The NYC Building Code used the "units of exit width" method for specifying exit capacity, in which each 22 in. unit of exit width provided the capacity for 60 people. Thus each 44 in. stairwell provided for 120 people and the 56 in. stairwell provided 2½ units, or 150 people, for a total occupant load per floor of 390.] 5.3.5 Egress Provisions The primary egress system for the office spaces was the three stairways located in the building core. There were four main requirements for these stairways: number, width (including separate width requirements for the doors), separation of the doors to the stairways, and travel distance to the stairway doors. The number of stairways and the width of the doors resulted from the implementation of the 1968 edition of the NYC Building Code, whose provisions were less restrictive than those in the 1938 edition. The 1968 code eliminated a fire tower (an enclosed staircase accessed through a naturally ventilated vestibule) as a required means of egress and reduced [57/107] ----- the number of required stairwells from six to three [9] and the width of the doors leading to the stairs from 44 in. to 36 in. Of the three staircases, two (designated A and C) were 44 in. wide; stairway B was 56 in. wide. The largest occupant load in the office spaces was 365 people per floor (36,500 ft2 on the largest floor, with 100 ft2 per person). Neither the 1968 NYC Building Code nor any of the contemporaneous codes mandated consideration of the number of building stories in determining the number and widths of the stairwells. For the floors classified in the office use group (all floors except the observation deck and restaurant/meeting spaces), a minimum of two stairwells would have been required to serve the occupants, each equally sized. The three modern building codes considered in this report [International Building Code (IBC) (2000), NYC Building Code (2003), and NFPA 5000 (2003)], as well as the 1968 NYC Building Code, were consistent in this requirement, each regardless of building height. However, the resulting width of these minimum requirements would differ. Two 44 in. stairwells would have satisfied IBC minimum requirements, two 65 in. stairwells would have satisfied NFPA 5000 requirements, and two 78 in. stairwells would have satisfied the 1968 and 2003 NYC Building Code requirements. Alternatively, as was built at WTC 1 and WTC 2, three stairwells of narrower construction, but equivalent or greater total required width, would also satisfy the egress requirements in the modern building codes. The 1968 NYC Building Code contained a requirement that the stairwells be "as far apart as practicable." Since the stairwells on the impact floors of WTC 1 were substantially closer together than those on the impact floors of WTC 2, it certainly was possible to have designed a greater separation in WTC 1. Local Law 16 (1984) added a quantitative requirement that the separation between exit door openings be at least one-third of the maximum travel distance of the floor. For the WTC towers, this maximum distance was 180 ft, and the smallest separation of stairwell doors was 70 ft. The towers were consistent with this requirement. NFPA 5000 (2003) and IBC (2000) incorporate a requirement that the separation of the stairwells be no less than one-third the overall diagonal length of the building. For the towers this length was 294 ft, and one-third was 98 ft. Thus, the stairwell separations on some floors would have been inconsistent with the later codes (with which the buildings in New York City were not required to comply). At the top of the two towers were floors that were classified as public assembly floors: the Windows on the World restaurant complex in WTC 1 (floors 106 and 107) and the Top of the World observation deck in WTC 2 (floor 107). The design number of occupants on each of these floors was over 1,000. On September 11, 2001, there were about 188 people in the Windows on the World and few in the Top of the World since it was before the opening hour. Thus, had the stairwells remained passable through the impact region, the capacity would have been sufficient for the occupant load observed on that morning. Nonetheless, the egress requirements for assembly occupancy were more stringent than for business occupancy in both the NYC Building Code in 1968 and in 1996, when the Windows on the World re-opened after refurbishment following the 1993 bombing in the basement. NIST found documentation that, in 1996, The Port Authority created areas of refuge consistent with the provisions of the 1968 NYC [9] See discussion of the required number of stairwells later in this section. [58/108] ----- Building Code, but NIST was unable to find evidence indicating that the requirements for the number of exits for the evacuation of over 1,000 people from each of these floors had been considered in the design or operation of the buildings. In 1995, the NYC Department of Buildings, however, had reviewed the egress capacity from these floors and apparently concurred that the proposed remodel to these spaces would meet the intent of the NYC Building Code. Subsequently, NIST communications in 2005 with The Port Authority and the NYC Department of Buildings identified a difference of interpretation regarding the number of exits required to serve these floors. The Port Authority stated that a fourth exit was not required since the assembly use space in question constituted less than 20 percent of the area of principal use, with principal use area defined as the entire building. The Department of Buildings stated that the 20 percent rule did not apply to assembly spaces such as restaurants and observation decks that are open to the public, and therefore exit reduction cannot be applied and a fourth exit was required. The Department further clarified that areas of refuge and horizontal exits are not to be credited for required means of egress (unless the spaces are used non-simultaneously) and that for places of assembly, with occupant load in excess of 1,000, the floor shall have a minimum of four independent means of egress (stairs) to street. If the floor were divided into areas of refuge with rated walls, as was the case for the WTC towers, each area is to be considered an independent place of assembly that needs its own access to two means of egress (stairs) without going through another assembly space if they have an occupant load of less than 500 each (or three means of egress if the area of refuge had an occupant load between 500 and 999). Further, since the only means of egress from the roof-top deck was through the space on the observation floor, the Department clarified that occupant load from the deck would need to be added to the occupant load of the observation floor and that the travel distance from the roof deck along the connecting stairs to the required means of egress at the observation floor shall be within the maximum permitted by the NYC Building Code. The Department, however, did not raise the issue of a fourth stairwell in its December 1994 meeting with The Port Authority and when it subsequently concurred with The Port Authority's proposal to remodel the spaces. Given the low occupancy level on September 11, 2001, NIST found that the issue of egress capacity from these places of assembly, or from elsewhere in the buildings, was not a significant factor on that day. It is conceivable that such a fourth stairwell, depending on its location and the effects of aircraft impact on its functional integrity, could have remained passable, allowing evacuation by an unknown number of additional occupants from above the floors of impact. If the buildings had been filled to their capacity with 20,000 occupants, the required fourth stairway would likely have mitigated the insufficient egress capacity for conducting a full building evacuation within the available time. * * * [59/109] Note: For the learning impaired, such as BAC, practicable is most definitely NOT a synonym for practical. They are two VERY different words. ----- ENCARTA practicable prac·ti·ca·ble adjective Definition: 1. capable of being done: capable of being carried out or put into effect 2. usable: capable of being used successfully [Mid-17th century. < French < practiquer "put into practice" < medieval Latin practica < form of Greek praktikos "practical" (see practice)] prac·ti·ca·bly adverb prac·ti·ca·bil·i·ty noun Word Usage practicable or practical? These two adjectives have overlapping meanings. Both indicate that something can be done, but practical also implies that it is appropriate, sensible, or useful: It is practicable to do the calculation in the traditional way, but far more practical to use a computer. The difference between impracticable and impractical is rather more clear-cut: impracticable means "impossible" and impractical means "not workable when put into practice." ----- NOTE: The Building Codes specify "practicible," not "reasonably practicible." This distinction serves to eliminate a consideration of cost in implementing that which is feasible or practicable. It is essentially the same throughout the English-speaking world as shown by the following examples from Austrialia and the UK. National Transportation Commission (Australia) Meaning of So Far As Is Reasonably Practicable (SFAIRP) * * * SFAIRP is a legislative qualification that is well known to the law and found in a number of statutes both in Australia and overseas. In essence, it requires weighing the risk against the resources needed to eliminate or reduce the risk. It does not require every possible measure to be implemented to eliminate or reduce risk, but it places the onus on the person holding the duty to demonstrate (or be in a position to demonstrate) that the cost of additional measures to control the risk (over and above those risk controls already in place) would be grossly disproportionate to the benefit of the risk reduction associated with the implementation of the additional risk control. ----- http://www.iosh.co.uk/index.cfm?go=discussion.view&forum=3&thread=24667 Re: PRACTICABLE RESONABLY PRACTICABLE (UK) Case: Adsett -V- K&L Steel Founders and Engineers Ltd [1953] Facts Mr Adsett contracted pneumoconiosis in a foundry. The main cause was silica dust which got into the air as a result of Mr. Adsett’s job This was to shovel various casting sands and compounds through a grate onto a conveyor belt below. He freely breathed in the resulting atmospheric dust. In a effort to control the emission of dust from the operation the employer installed a dust extractor near the conveyor. They did this as soon as the idea had been thought of. However this was well after the onset of Mr. Adsett’s disease and too late to save him from disablement. Decision The question in this case concerned the meaning of the word “practicable”, the ordinary dictionary definition was “possible to be accomplished with known means or resources” (Websters Dictionary) or “capable of being carried out in action” or “feasible” (Oxford dictionary) The word practicable on its own connoted a stricter standard than “reasonably practicable” and may mean the question of cost should be eliminated. But no measure could be practicable if it was not within current knowledge and invention. It was argued that the technology to install such an extractor did exist, but the employers (and everyone else in the industry had not thought of this particular application for an extractor. The court held that “practicable” meant that a measure had to be known for its application by people in the industry and especially by experts; as this was not the case the claim failed. another example Case Moorcroft -V- Thomas Powles & Sons Ltd [1962] A plasterer was laying sand and cement screed on a newly constructed flat roof. There was an opening in the roof about 5 foot by 3 foot. This opening had an upward projecting timber edge around its perimeter. while working, the plasterer stepped backwards, tripped on the edging and feel 11 feet through the roof. A prosecution was brought under Building Regulations which required that all such openings should be made safe by the provision of guard rails, etc. If special circumstances render compliance impracticable then such compliance or other measures as are “practicable” must be taken. The court held that “practicable” imposed a stricter standard than “reasonably practicable”, and said that “practicable” excluded consideration of cost. In this case it would have been practicable to have put a board over the opening. The simplicity of this measure overrode the necessity for the plasterer to work quickly so as to covet the roofing structure before the weather broke. Post Comment Private Reply Ignore Thread
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