Empire State Building

RF-Based Firefighter Communication Performance in Buildings

2013-05-22:  Whatever Service Providers claim … every day, we experience mobile/cell phone reception variability, drop-off and failure in buildings … whether we are fully conscious of it or not.  It’s inconvenient, but all we have to do is change location, even slightly … and ‘re-dial’.  However, if we are travelling on a train or bus, and it enters a tunnel … the problem can be annoying, as the situation is beyond our control !

On the other hand, however … not too far from where I live, there is an art house cinema with underground screens on different levels.  In this particular case, mobile/cell phone reception failure can be a positive joy – it will not be necessary to listen to someone else’s loud conversations during the film !

BUT … emergency first responders use radio frequency-based communication systems during the normal course of their work … and in the current built environment, these systems can also be unreliable.  Improved climate resilience in our future building stock will make matters worse.  So, it makes a lot of sense to take this issue seriously now !

Fire Departments equip their firefighters with a Radio Frequency-Based Personal Alert Safety System (PASS) … also known as an Automatic Distress Signal Unit (ADSU) … which sends out a signal to a fire incident base / control centre / command post when the firefighter is motionless or in distress, with a clear indication of his/her location … or, if necessary, a general warning can be sent from the fire incident base / control centre / command post to all firefighters to evacuate a building immediately … for example, if extensive structural collapse is imminent.

Recently, the National Institute of Science & Technology (USA) issued Technical Note 1792.  I have just a few short comments to make before jumping into the document …

1.   The Empire State Building and a Subway Station in New York City are both iconic building types … and unusual, in the context of the USA generally … but not so in Europe, with our long tradition for ‘hard/heavy’ construction.  Challenging environments for radio frequency-based communication systems are encountered in our basement / underground building types, and low-rise complex building types … never mind high-rise and tall buildings.

2.   Outside buildings, adequate external access routes for Firefighting Vehicles are mandated in building codes and standards … and Firefighter Lifts are provided inside buildings, etc., etc., etc.  Facilitating reliable radio frequency-based emergency communications should become a normal part of thinking about … and designing for … Safe Firefighter Access.  And … before new buildings are occupied, it should become routine to carry out an emergency communications check, as part of a wider collaborative effort between Building Management Teams and Local Fire Services.

3.   This NIST Technical Note is further evidence … as if any more evidence were needed … that it is a continuing and difficult process to fully implement the 2005 & 2008 NIST WTC 9-11 Recommendations.  To date, the easier low hanging fruit (system and procedural inadequacies !) have been tackled, which may be presented and/or described as substantive changes in building codes and standards … mere window dressing … tokenism, at its worst !   However, as discussed here before many times, some European countries continue to completely ignore these important NIST Recommendations.

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NIST Technical Note 1792 (March 2013) - Title Page

Click to enlarge.

March 2013 – NIST Technical Note 1792: ‘Performance Analysis of RF-Based Electronic Safety Equipment in a Subway Station and the Empire State Building’.

To Read/Download NIST TN 1792 (PDF File, 9.02 MB), go to … http://dx.doi.org/10.6028/NIST.TN.1792

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NIST TN 1792 – Summary & Conclusion (Page 59)

Radio Frequency (RF) PASS Tests were performed in a New York Subway Station and the Empire State Building because these types of structures provide challenging RF propagation-channel environments.  In the Subway, the RF PASS systems were limited in their ability to communicate beyond the initial entrance level.  Without the use of repeaters, most of the systems could communicate only a short distance beyond the bottom of the stairwell that connected the token booth corridor to the street.  Two systems used repeaters to extend the coverage area.  When a repeater was located at the base of the stairwell leading up to the street, those two systems were able to communicate the RF PASS alarms between the street level and the first passenger platform.  However, with only a single repeater, neither of the two repeater systems was able to communicate between the external receive site and the second passenger level.  This suggests that for structures with sizable subterranean sections, a repeater system will likely be required to reach an external incident command post.  If the structure has multiple subterranean levels of increasing depth, a multiple-hop relay system will likely be necessary to ensure the reliability of the communication channel.

NIST TN 1792 - Figure 16: 'Subway + System 4 Performance'

NIST TN 1792 – Figure 16: ‘Subway + System 4 Performance’. Click to enlarge.

In the path-loss measurements and analysis performed at five frequencies, ranging from 430 MHz to 2405 MHz, there are several important insights.  Based on the upper adjacent values in the box-plot statistical representation of the path-loss data from the Empire State Building (see Figure 36), path-loss values of 140 dB to 175 dB are possible for high-rises.  For the Subway, the path-loss values exceed 210 dB to 240 dB at the lower two passenger platforms (see Figure 35).  The frequency dependence is more pronounced for the Empire State Building results, but less apparent in the Subway data.  Thus, while a system may function well at the lower end of the frequency spectrum in the above ground portions of a large building, the subway results demonstrate that subterranean structures can cause path-loss values greater than 200 dB across the 430 to 2400 MHz range.

NIST TN 1792 - Figure 21: 'Tall Building + System 4 Performance'

NIST TN 1792 – Figure 21: ‘Tall Building + System 4 Performance’. Click to enlarge.

The testing completed here focused on RF PASS system performance and RF propagation-channel measurements in a high-rise and subway station.  While a primary goal of the effort was to look at the correlation between the system performance and path-loss behaviour, a secondary goal was to gather path-loss data in two high-attenuation settings.  Thus, parameter values for log-normal distributions that will allow simulation of the measured path-loss conditions are included in this report.  The authors hope that the data presented here, along with future sets of data, can be used to develop a complete suite of test methods, not only for RF-based PASS systems, but also for other RF-based electronic safety equipment.  The path-loss values obtained here are general and could be used to develop standards for other equipment as the need arises for standards for these systems.

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In Ireland … 10 UHF Channels have been allocated to the Fire Services for use with hand portable radios …

Ireland: The Fire Services Council's Firefighter Handbook (2001) - Table 2.4.2

Ireland: The Fire Services Council’s Firefighter Handbook (2001) – Table 2.4.2. Click to enlarge.

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NIST WTC Recommendations 25-28 > Improved Practices

Previous Posts in This Series …

2011-10-25:  NIST’s Recommendations on the 9-11 WTC Building Collapses … GROUP 1. Increased Structural Integrity – Recommendations 1, 2 & 3 (out of 30)

2011-11-18:  NIST WTC Recommendations 4-7 > Structural Fire EnduranceGROUP 2.  Enhanced Fire Endurance of Structures – Recommendations 4, 5, 6 & 7

2011-11-24:  NIST WTC Recommendations 8-11 > New Design of StructuresGROUP 3.  New Methods for Fire Resisting Design of Structures – Recommendations 8, 9, 10 & 11

2011-11-25:  NIST WTC Recommendations 12-15 > Improved Active ProtectionGROUP 4.  Improved Active Fire Protection – Recommendations 12, 13, 14 & 15

2011-11-30:  NIST Recommendations 16-20 > Improved People EvacuationGROUP 5.  Improved Building Evacuation – Recommendations 16, 17, 18, 19 & 20

2011-12-04:  NIST WTC Recommendations 21-24 > Improved FirefightingGROUP 6.  Improved Emergency Response – Recommendations 21, 22, 23 & 24

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2011-12-07:  SOME PRELIMINARY COMMENTS …

  1.     Concerning Recommendation 25 below … yes, this Recommendation applies to the types of organizations identified in the text, but it should also be understood as applying to ALL Organizations … public or private, governmental or non-governmental or quasi-governmental, whatever, etc … ‘supported’ (see the text further down in Recommendation 25) with rigorous enforcement, in all cases, by publically appointed building control officials and/or by private, independent, competent technical control professionals.

Once more … and again and again (!) … confirmed by the sort of debacle seen at the Priory Hall Apartment Complex, in Dublin … Self-Certification / Self-Approval, i.e. ‘lite’ regulation, does not work.  For National Authorities Having Jurisdiction (AHJ’s), however, it is a cheap solution to a difficult, resource-devouring issue, i.e. protecting society and the consumer … in that order.

  2.     Concerning the Footnote to Recommendation 26 below … the choice should never be between either Fire Compartmentation or Sprinklers … or the other way around, whichever you prefer.  Neither is 100% reliable !

Fire Compartmentation

The division of a building into fire-tight compartments, by fire and smoke resisting elements of construction, in order …

  • to contain an outbreak of fire, and to facilitate effective firefighting ;
  • to prevent damage, within the building, to other adjoining compartments and/or spaces ;
  • to protect a compartment interior from external fire attack, e.g. fire spread across the building’s facade or from an adjacent building ;
  • to minimize adverse, or harmful, environmental impacts outside the building.

As developed as that definition is above, Fire Compartmentation should be regarded as just one Fire Safety Strategy / Fire Engineering Strategy … not the only strategy, and certainly not the main strategy.

Here are two reasons why not …

a)   The connection between compartment size and the ability to effectively fight a fire within a space of limited volume has been lost … so more and more, commercial pressure is being exerted on national authorities to expand the acceptable compartment sizes in buildings … which significantly increases the fire hazard ;

[ Remembering the difference between the limited Fire Safety Objectives of Building Codes/Regulations and the much broader Project-Specific Fire Engineering Objectives of Ethical Fire Engineering required to protect society and the full interests of our clients … it is easy to understand why national authorities feel that they can respond positively to such commercial pressures.]

b)   In a Sustainable Building … it is a very common design strategy to take advantage of the natural patterns of air movement in a building, for either cooling or heating purposes, depending on local climate conditions.  So there is simply no compartmentation, as understood in conventional fire engineering terms … and this throws up a fundamental conflict between the two.  To be discussed in another post !

  3.     Concerning the 2nd Footnote to Recommendation 28 below … in the very same New York City … at 09.40 hrs on a Saturday morning, 28 July 1945 … lost in fog, a B-25 Bomber slammed head-on into the 79th Floor of the Empire State Building … and caused enormous damage.  That building is still standing today … and surprise, surprise … there was aviation fuel in the B-25 !

In a similar vein … Fire-Induced Progressive Collapse was not observed for the first time, in New York, on 11 September 2001 !

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2005 NIST WTC RECOMMENDATIONS

GROUP 7.  Improved Procedures and Practices

The procedures and practices used in the design, construction, maintenance, and operation of buildings should be improved to include encouraging code compliance by non-governmental and quasi-governmental entities, adoption and application of egress and sprinkler requirements in codes for existing buildings, and retention and availability of building documents over the life of a building.

NIST WTC Recommendation 25.

Non-governmental and quasi-governmental entities that own or lease buildings and are not subject to building and fire safety code requirements of any governmental jurisdiction are nevertheless concerned about the safety of building occupants and responding emergency personnel.  NIST recommends that such entities be encouraged to provide a level of safety that equals or exceeds the level of safety that would be provided by strict compliance with the code requirements of an appropriate governmental jurisdiction.  NIST further recommends that as-designed and as-built safety be certified by a qualified third party, independent of the building owner(s).  The process should not use self-approval for code enforcement in areas including interpretation of code provisions, design approval, product acceptance, certification of the final construction, and post-occupancy inspections over the life of the buildings.*

[ * F-46  The long-standing stated policy of the Port Authority of New York & New Jersey (PANYNJ) was to meet and, where appropriate, exceed the requirements of local building and fire codes, and it entered into agreements with the New York City Department of Buildings and the Fire Department of the City of New York in accordance with that policy.  Although the PANYNJ sought review and concurrence from New York City in the areas listed in the Recommendation, the PANYNJ was not required to yield, and appears not to have yielded, approval authority to New York City.  The PANYNJ was created as an interstate entity, a ‘body corporate and politic’, under its charter, pursuant to Article 1, Section 10 of the United States Constitution permitting compacts between states.  Further, there are many other similar non-governmental and quasi-governmental entities in the U.S.  A comprehensive review of documents conducted as part of this Investigation suggests that the WTC towers generally were designed and maintained consistent with the requirements of the 1968 New York City Building Code.  Areas of concern included fireproofing of the WTC floor system, height of tenant separation walls, and egress requirements for the assembly use spaces of ‘Windows of the World’ in WTC Tower 1 and the ‘Top of the World’ Observation Deck in WTC Tower 2.  These areas of concern did not play a significant role in determining the outcomes related to the events on 11th September 2001.]

NIST WTC Recommendation 26.

NIST recommends that state and local jurisdictions adopt and aggressively enforce available provisions in building codes to ensure that egress and sprinkler requirements are met by existing buildings.*  Further, occupancy requirements should be modified where needed (such as when there are assembly use spaces within an office building) to meet the requirements in model building codes.  Provisions related to egress and sprinkler requirements in existing buildings are available in such codes as the International Existing Building Code (IEBC), International Fire Code, NFPA 1, NFPA 101, and ASME A 17.3.  For example, the IEBC defines three levels of building alteration (removal and replacement or covering of existing materials and equipment, reconfiguration of space or system or installation of new equipment, and extending the work area in excess of 50% of the aggregate area of the building).  At the lowest level, there are no upgrade implications for sprinklers and the egress system.  At the next level, sprinklers are required in work areas serving greater than 30 people if certain other conditions related to building height and use such as shared exits also are met.  There are numerous requirements for means of egress, including number of exits, specification of doorsets, dead-end corridors and travel distances, lighting, signage, and handrails.  At the highest level, the sprinkler and egress requirements are identical to the second level without the minimum 30-person restriction and the other conditions related to building height and use.  The Life Safety Code (NFPA 101) applies retroactively to all buildings, independent of whether any work is currently being done on the building, and ASME A 17.3 applies retroactively to all elevators as a minimum set of requirements.

[ * F-47  The WTC towers were unsprinklered when built.  It took nearly 28 years after passage of New York City Local Law 5 in 1973, which required either compartmentation or sprinklering, for the buildings to be fully sprinklered (the Port Authority chose not to use the compartmentation option in Local Law 5).  This was about 13 years more than the 15-year period for full compliance with Local Law 5 that was set by Local Law 84 of 1979.]

NIST WTC Recommendation 27.

NIST recommends that building codes incorporate a provision that requires building owners to retain documents, including supporting calculations and test data, related to building design, construction, maintenance, and modifications over the entire life of the building.*  Means should be developed for off-site storage and maintenance of the documents.  In addition, NIST recommends that relevant information be made available in suitably designed hard copy or electronic formats for use by emergency responders.  Such information should be easily accessible by responders during emergencies.  Model Building Codes:  Model building codes should incorporate this Recommendation.  State and local jurisdictions should adopt and enforce these requirements.

[ * F-48  The availability of inexpensive electronic storage media and tools for creating large searchable databases makes this feasible.]

NIST WTC Recommendation 28.

NIST recommends that the role of the ‘Design Professional in Responsible Charge’* be clarified to ensure that:  (1) all appropriate design professionals (including, e.g. the fire protection engineer) are part of the design team providing the highest standard of care when designing buildings employing innovative or unusual fire safety systems;**  and (2) all appropriate design professionals (including, e.g. the structural engineer and the fire protection engineer) are part of the design team providing the highest standard of care when designing the structure to resist fires, in buildings that employ innovative or unusual structural and fire safety systems.  Affected Standards:  AIA Practice Guidelines.  Model Building Codes:  The International Building Code (IBC), which already defines ‘Design Professional in Responsible Charge’, should be clarified to address this Recommendation.  NFPA 5000 should incorporate the ‘Design Professional in Responsible Charge’ concept, and address this Recommendation.

[ * F-49  In projects involving a design team, the ‘Design Professional in Responsible Charge’ – usually the lead architect – ensures that the team members use consistent design data and assumptions, co-ordinates overlapping specifications, and serves as the liaison between the enforcement and reviewing officials and the owner.  This term is defined in the International Building Code (IBC) and in the International Code Council’s Performance Code for Buildings and Facilities (where it is the Principal Design Professional).]

[ ** F-50  If the fire safety concepts in tall buildings had been sufficiently mature in the 1960’s, it is possible that the risks associated with jet-fuel ignited multi-floor fires might have been recognized and taken into account when the impact of a Boeing 707 aircraft was considered by the structural engineer during the design of the WTC towers.]

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