Published on: 18-May-2020, 02:41 PM     

Fire Safety Engineering &Prescriptive Codes Conflicting or Complemental?

By: Abhay D Purandare: M.Eng(FPE), FIFireE, FIFE, PMSFPE

1.0 Introduction

 

Currently, there are two basicapproaches to fire and life safety design of buildings – the traditional code based (or prescriptive) approach, and the relatively new fire engineering or FSE (Fire Safety Engineering)/ PBD (Performance Based Design) approach. The fact is that outside a handful of developed countries where it is accepted, FSE/PBD is mostly unheard of. Most of the world, including our country, is comfortable following a prescriptive code based approach to fire and life safety design. Feeble attempts have been made for introducing FSE/PBD alternatives to code based design, but have been unsuccessful. The reasons for this are varied, but primary among them is a strong feeling of insecurity amongst stakeholders, mainly the authorities and real estate sector, and a general feeling that the knowledge and competence to apply this design approach is not available presently. There is also a belief that the latter approach results in more expensive designs, while following code based designs is simpler, faster and cheaper.There is no doubt that while code based design can be applied to standard building designs, it is unable to provide design solutions for complex or unique buildings. While FSE/PBD approach is not allowed as per current building regulations / codes in the country, the door is not entirely shut on this option. This is because many jurisdictions (as is also stated in NBC Part 4) will accept engineering analysis/ performance based options for deviations in an otherwise code based design approach, typically to justify non-compliant egress designs, or for smoke control systems not adequately covered by codes.This implies that even in code based regimes, there is an acceptance, although limited in scope, of FSE. Whether these two approaches can work to support, and complement each other is the question to be explored. To do so, it would be appropriate, at this stage, to take a look at the background and development of these two approaches.

 

2.0 Prescriptive Codes

 

Prescriptive codes have a long history. Even ancient civilizations recognized the risks posed by fire to life and property and realized that this problem cannot be addressed by individuals but had to be tackled at a societal level. Like modern building codes, these rules and laws too were a reaction to devastating fire experiences and loss of lives and property. As an example, rules in ancient Rome required open space of five feet between all adjacent buildings, limiting height of buildings to 70 feet, and the use of stone instead of wood for buildings [1]. In ancient India (as early as 2nd century BCE), manuscripts such as Kautilya’sArthashastra had recommendations for the prevention of fire such as locating professions using fire at one place, roofs made of grass/mats to be removed, and collection of water jars at junctures. Interestingly, the manuscript also provides for punishments and fines for citizens not following fire prevention practices or indulging in arson [2].

 

2.1 Modern Building Fire Codes

Building fire codes are based on past experience and empirical data. Major fire accidents and their adverse effects result in appropriate changes and modificationsto codes.Modern building laws followed devastating fires such as the ‘Great Fire of London’ (1666), which required houses in London to be built from stone instead of wood, and wider road to allow more space between houses. In 1774, the Fire Prevention Act was implemented in UK which called for arrangements for safe escape of building occupants in a fire, thus addressing life safety issues for the first time. This was a precursor to later building fire legislation in the UK such as the London Building Act & Bye-Laws (ca. 1930), the Fire Precautions Act (1971), and later acts. In the USA, the first formal legislation resulted after the ‘Great Fire’ of Chicago (1871), which introduced spacing between buildings and requirements related to construction materials. Another importantincident which affected building rules was the Triangle Shirtwaist Factory fire (1911), whichresulted in the real development of the NFPA 101 (Life Safety Code), and recommended better fire proofing, sprinkler systems and improved exit arrangements for high-rises, [3].

Within the country, Calcutta Fire Brigade came under the Municipal Corporation by 1872, and fire regulations began to be framed for buildings. The enactment of the Bombay Municipal Corporation Act in 1888,formally brought the protection of life and property from fire under the ambit of the Municipal Corporation. The Planning commission appointed a panel of Experts in 1965 to study the problem of different building regulations throughout the country and an important recommendation of this study was that a National Building Code be prepared to standardize the building regulations for use by government departments, municipal bodies and other agencies. The first version of the code was published in 1970, which was first revised in 1983 and then in 2005. The latest revision of the code is the 2016 version, released in 2017.

 

3.0 Fire Safety Engineering

 

Fire Safety Engineering is defined by the British Standards Institute as ‘the application of scientific and engineering principles to the protection of people, property and the environment from fire’[4]. FSE has its roots in scientific principles and fire research, and as per Quintere[5]“Fire research activities may have begun as early as 1920 but these were insignificant to the large scope of the field. Early studies were focused on ensuring adequate fire resistance of building structural elements. In most probability, 1950 is the nominal starting date of the birth of modern fire science and research. The studies from this period began to address the dynamics of the fire and the movement of smoke. Damage to people and contents were now considered more important than just the building structure”.

 

In Japan, fire research was driven by the country’ vulnerability to earthquakes and subsequent fires, andKawogoe (BRI) was the most significant pioneering fire scientist here. In the UK, P. H. Thomas and David Rasbashled British fire research from the early 1950's, at the Fire Research Station. At about the same time, Prof. Howard Emmons (Harvard), encouraged by Prof. Hottel (MIT), began to advocate for basic research in the field of fire. Fire research in the USA got further impetus from the 1970sonwards after the ‘America Burning’ report was tabled. Though not very clearly documented, significant work also went on Soviet countries during this period, and they conducted pioneering studies in combustion[5].

3.1 Present Status of FSE

Since the 1970’s, there has been significant fire research all over, with significant contributions from Europe (Sweden, Belgium), UK, New Zealand, USA and Japan, to name a few. This has resulted in a wealth of information being assimilated and published with respect to fire research. The main areas of fire research which have seen significant work done are:

• Dynamics of fire plumes, smoke flow under ceilings, room fires flashover

This has provided an understanding of how fires grow within compartments, the feedback of heat from flames to fuel surfaces, the phenomenon of breakdown of fuel structure under heat, the formation of flames, products of combustion, size and flow of fire plume, its movement under ceilings and interaction with compartment surfaces. This knowledge, along with empirical equations, allowed scientists and engineers to calculate and predict fire growth in compartments. When used withthe transient, three-dimensional Navier-Stokes equations and related equations for species and energy conservation in fires using turbulence models for turbulent transport, it formed the basis of currently used CFD models for fire growth modeling.

• Dynamics of fire effects on simple structural elements

Using the knowledge gained above, it was possible to assess the heat generated in compartment fires and applying laws of physics, to predict the heat transfer and temperature rise in structural elements. Based on empirical data, and techniques such as such as finite element analysis, models have been developed to predict their behavior in fire. It is also possible to evaluate and assess the performance of different insulating (fire resistant) material applications on structural members. Due to the large variety of construction materials, a lot of research still continues on different structural elements to assess their load bearing, insulation and other properties when exposed to fire.

• Smoke movement in simple building geometries

Based on combustion dynamics and chemistry, it is possible to assess the amount of smoke and combustion gases generated based on the composition of fuel involved, and ventilation available (a large number of fuels have now been tested for their fire properties and a significant database is now available). Fire dynamics allows to predict smoke movement using factors such as buoyancy of fire gases, stack effect, building ambient temperatures, tightness, etc. This is very useful tool in the design of smoke control systems (and models based on this, are commonly employed currently for smoke control system design). This is also useful for predicting activation of devices such as sprinklers, heat/ smoke detectors, and for evaluating the tenability conditions in a given zone.

• Effects of fire and products of combustion on people

Substantial research has been carried out on in the UK and USA over the last 4 decades to assess the effects of fire gases on occupants. Expectedly, this has been done using surrogates (animals, by exposing them to combustion gases using different kinds of fuels and ventilation conditions). With some correction, it has been possible to extrapolate the same for humans. Empirical equations have been developed to evaluate the combined effects of different fire gases on the human body e.g. the Fractional Effective Dose (FED) and Fractional Irritant Concentration (FIC) equations (much work has been done in the UK by Dr. Purser). Obscuration effects of smoke and its effects on occupants, has been researched extensively in Japan (Tadahisa Jin).

• Movement & emergency evacuation of People

On the other hand, scientists have also attempted to studyoccupant movement and related factors, such as speed (in vertical and horizontal directions), effect of crowding, movement through egress components (doors, stairs), etc, and provided empirical equations which give consistent and realistic results. More complex and difficult to quantify, however, is the behavior of occupants when faced with a fire situation, though some data has been compiled in this regard as well. All this forms the background of evacuation models, which alongwith the effects of products of combustion of a fire, can be used to assess evacuation from a given space for a given population. This is being done quite commonly on projects which have large occupant populations such as airport terminals, metro stations, large theatre buildings, sports arenas and malls.

• Basic knowledge ofinteraction of suppression agents with fire

This is an area where more research is required and being encouraged. The fact is that while there is lot of testing going on in the private sector and substantial empirical data is available, it is still not possible to use first principles to describe interaction of fire suppression agents with fires. Scientists have developed basic equations for water based suppression (fire point equation) and gas based suppression (adiabatic flame temperature concept), however these need further research and refinement before they can be confidently applied to real world problems. Some attempts have also been made to use existing knowledge of water based suppression (flame cooling, inerting effects) by sprinklers/ water mist systems, in models like FDS to predict suppression, which have been validated with small scale experiments, but need further research and validation for large size fires before becoming useful.

4.0 Fire Safety Engineering Knowledge & Codes

 

At this stage, it is pertinent to look at how current fire safety research is impacting fire safety field and whether this knowledge has relevance to the prescriptive (code) based approach as well. In recognition of the substantial research carried out in this field and the knowledge/data gained, many countries now have accepted the field of fire engineering as a separate engineering branch. These include countries listed under 3.1, most of whom accept that‘this knowledge enables the results of recent research into fire and human response to be translated directly into the building design process’[4]. Codes such as NFPA 101 allow performance based design alternative, and has included a chapter to provide guidance on this approach. Similarly, in the UK, the Approved Documents (building codes) clearly state that ‘these are intended to provide guidance for some of themore common building situations, but there may well be alternative waysof achieving compliance with the requirements. Thus, there is no obligation toadopt any particular solution contained in an Approved Document if you prefer tomeet the relevant requirement in some other way. (Approved Document B)'. New Zealand has been a pioneer in FSE practice, where it was introduced over 3 decades ago, and Australia too accepts a Fire Safety Engineering approach to building design. Many European countries too accept the FSE approach as an alternatie, while a number of other countries, who otherwise follow a prescriptive (code based) approach will still accept performance based solutions to deviations/ non-compliances in designs, which cannot be addressed through codes. 

 

These countries recognize that the fire safety engineering knowledge gained through fire research,and principles developed have undeniable value in improving fire safety, and current FSE/ PBD practices are robust enough to allow it to be formalized into a proper engineering practice; onewhich can be applied into the building design process as an alternative to building codes. It is now over three decades since FSE/ PBD designs have been practiced; a long enough period for it to be gain acceptance as a sound engineering practice at best, or as an alternative worth considering, at worst. The fact that it is gaining acceptance in countries where it was not considered before, is proof of its increasing influence and recognition in enhancing fire safety. While codes are reviewed periodically in light of new developments and accidents, fire safety engineering taps directly into the now substantial body of knowledge and data acquired from fire research to provide new and viable solutions.A number of building fire code provisions related to fire resistance, egress provisions, fire detection and fire protection can be better understood, or reviewed, based on this new knowledge. Some examples given below:

4.1 Fire Resistance & Structural Behaviour

Fire research has provided sufficient knowledge about fire behavior of materials, effect of ventilation, building configuration and lining materials to confidently predict fire growth and its effects in compartments. For e.g. on a building project in the UK, while the fuel loading was high, the HRR of a resulting fire was calculated to be comparatively lower, due to the smaller opening (ventilation) size available; the authorities accepted lower fire resistance for structural members when presented with this finding. New research clearly shows that while fuel loading can be used as an indication of the fire hazard, it is not necessarily the only factor to be considered, as other factors will also have a bearing on fire growth in a building.

On the other hand, if sufficient ventilation is available, fires in modern homes are expected to be hotter and more intense (due to the kind of fuels available today), which  means that the building structure will be exposed to higher temperatures than earlier.  As real world fires are different from standard fire tests to which structural elements are subjected, structural behavior models allow accurate prediction of behavior in fires.

4.2 Egress Design & Occupant Behaviour

 

To believe that our homes and buildings and the fires that affect them have remained the same since the introduction of building codes would be naivety. Fire professionals are aware of how introduction of new materials and changes in design and construction techniques are posing new challenges for occupants and firefighters. For e.g. the type of furnishings and lining materials have a huge impact on fire growth and toxicity of fire gases, and travel distances and exit capacities may need to be reviewed in light of this knowledge. Large building spaces allow smoke filling, and would allow longer egress times as compared to smaller compartments.

Reactions of occupants to fire alarms and other cues are now better understood and documented, and should be considered when assessing code based egress designs for e.g. it is clear that voice evacuation messages or the presence of uniformed (and trained!) personnel greatly improves evacuation times. Reaction to loss of visibility has been found to be different for different countries and location of exit signs may have to be done accordingly. Many new behavior based evacuation models use this data to predict evacuation scenarios.

4.3 Fire Detection & Fire Protection Systems

Fire dynamics has greatly enhanced the knowledge of how fire detection and fire suppression systems interact with fires. Based on type of fuels available and other relevant factors, activation of detectors may vary greatly and hence this should be considered keeping in view life safety assessment. It is now clear that it is the ceiling fire plume which is responsible for activating smoke/heat detectors and/or sprinklers and not the radiated heat from the fire. Therefore location of these devices (especially sprinkler heads) needs to be properly planned (current practice of lowering sprinkler heads to obtain quicker activation should be clearly discouraged).

Interaction of water droplets (from sprinklers/ spray nozzles) with flames has been researched extensively, and with advent of water mist systems, this is still being further studied. Water application rates for handline nozzles (to be used with building hydrant systems), hose reels, etc, need to be evaluated in light of this knowledge. Similarly water spray application rates for radiant heat protection can be reviewed/validated.

4.4 Smoke Control Systems

Marked progress has been made in understanding smoke generation and behavior in fires. New building features such as atriums, internal stairs and the practice of having deeper and larger basements have provided impetus to these studies. It may be noted that current prescriptive requirements for smoke control systems also allow the option of an engineering analysis in NBC Part 4, which is an acknowledgement of the relevance of this knowledge and research. In fact, for many building applications, even the AHJs accept that a FSE/PBD approach may be the only realistic option.

Knowledge of building fuel loading, ventilation conditions and fire growth knowledge can help in accurate prediction of smoke generation and assess whether prescriptive requirements for smoke control would indeed be effective.

4.5 Validation of Code Provisions

Many code provisions have remain unchanged over time, without the actual intent behind such provisions either not clearly understood or appreciated. Similarly, new provisions may have been introduced without it’s actual effectiveness having been understood or demonstrated satisfactorily. FSE/PBD tools can be used for justification and/or contradiction of such provisions based on latest findings, research, and calculations.

 

5.0 Inputs/Knowledge From Codes

 

Building codes are based on experience, and new incidents continue to add to this experience and consequently, to codes. Major findings from incidents bring about changes/ modifications in codes. For e.g. the Station Nightclub incident of 2001 clearly highlighted how patrons prefer to use the same path to exit, from where they came in (consequently, main entry doors need to have width to accommodate 2/3rd of the occupant load. This was clearly a new aspect of occupant evacuation behavior which also provides useful inputs to FSE field.

 

In 2004, a large college building at Delft University, Netherlands, collapsed following a fire which started from a coffee machine; this was clearly a case of abnormal structural failure. A similar incident within the country, now known as the ChennaiSilks fire of 2017 resulted in sustained burning,inspite of gallant firefighting efforts, causing collapse of the building. Other abnormal incident findings related to effect of fire effluents on occupants, behavior of materials/ structural elements, response of active fire protection systems, etc, provide the FSE field with new findings and areas to research and develop.

 

Building codes are based on years (decades!) of experience and conventional wisdom, and just because FSE design alternatives are available, they need not be applied without first critically evaluating equivalent code provisions. Analysis of such provisions could provide interesting (and hitherto overlooked) information/knowledge to FSE practitioners.

 

6.0 The Way Forward

 

Fire services and engineering/design professionals are two key stakeholders in the building design process, and due to an established comfort level with a code based regime, there is an inherent resistance to acceptance of FSE as a practice. An article on this subject summarized that ‘that code provisions are considered biblical (without any need for justification), while FSE based solutions need to undergo a high level of scrutiny for consideration’ [7].  The Fire Service (being a disciplined, emergency response force), is understandably reluctant to accept new methods and solutions propagated by FSE practitioners, which arises due to the lack of knowledge and confidence on FSE concepts and practices. In many countries, however, including in Asia, FireServicesare recognizing the need for trained scientific personnel within their ranks.

 

While many countries do not have the depth of scientific knowledge, and the technical resources to accept FSE as an acceptable alternative to prescriptive codes, at the same time its relevance in a code based regime must be appreciated. ‘FSE knowledge and tenets also find application in a code based environment; it helps to understand and appreciate the underlying concepts behind many code provisions, some of which are not fully understood in third world’[6]. At the same time, rapid changes in construction techniques, unusual designs, and use of new materials are posing new challenges to code implementation; using the now substantial body of knowledge and data acquired from fire research, it is possible for FSE to provide solutions where codes fail to do so.As pointed out in a relevant article, there is a need for Fire Engineers ‘to understand what codes are saying effectively in engineering terms and to understand flaws that are not scientifically based’.

 

Wisdom lies in convincing proponents of a code based approach that FSE is not a threat to existing fire safety wisdom, but important complementary knowledge that can help better understand, support and improve their own fire safety codes. For it to find acceptance, FSE needs to be positioned not as an adversary, but as an important partner to ensuring safe building designs.

 

Bibliography

[1] Canter H.V, ‘Conflagrations in Ancient Rome, available at  http://penelope.uchicago.edu/Thayer/E/Journals/CJ/27/4/Conflagrations*.html accessed 22 July, 2019

[2] Bapat, Asawari, Disaster Management in KautilyaArthasastra, aWEshkar Vol. XVII Issue 1 March 2014 WeSchool

[3] http://www.dps.state.ia.us/fm/inspection/history/History_of_Fire_and_Fire_Codes.pdf accessed 23July, 2019

[4]  PD 7974-0:2002, Guide to design framework and fire safety engineering procedures, BSI, 2002

[5] Quintere James, Progress In Fire Science

[6] Purandare, A, FSE in the Third World, International Fire Professional, Nov 2018, Issue No 26

[7] Bullock, Monaghan “Code compliance or Fire Engineering for Life Safety Design – Have We moved On?” International Fire Professional, April 2014, Issue No. 8

 

 

 

About the Author

 

Abhay D. Purandare is a Fire & Life Safety Specialistt, based out of Ahmedabad, with an experience spanning 3 decades, in both industrial and infrastructure sectors. He is a Master in Fire Protection Engg from the University of Maryland a Fellow of the Institution of Fire Engrs (UK) & (India), and a Professional Member of the SFPE (USA). He has worked in India and the Middle East, in areas of fire & life safety design, firefighting equipment design & development, higher education in Fire engineering, and major project engineering consultancy. He has also published extensively with the sole objective of promoting the interest of fire safety.