By Peter Johnson, CP. Eng.
For many people, the world changed on 9/11.
Among the many new concerns brought about by that tragedy, fire safety has become a front-and-center issue for building owners and managers, local authorities, construction contractors, architects and fire protection engineers.
The latter group has been working particularly hard since Sept. 11th to debunk many prevalent myths about fire safety. These myths are perpetrated not only by lay persons, but by building design professionals (who, you would think, should know better).
Let's examine the seven most prominent fire safety myths, see where they spring from and decide whether they have any foundation in reality.
Myth 1: All Occupied Buildings Require Sprinklers
There's no doubt sprin-klers offer huge life safety and proper-ty protection benefits, with very few deaths occurring in sprinkler-protected buildings. But countries in the United Kingdom, for example, allow apartments and offices to be built to heights of as much as eight stories with-out sprinklers and their record on life safety is certainly no worse than that of other nations. (Even acute-care hospitals are built in the UK without sprinklers.) Moreover, countries such as Germany that rely less on sprinklers have no significantly greater loss of life in occupied buildings.
Myth 2: People Always Panic in a Fire
A second commonly maintained myth holds that people will panic in the event of fire. Even many fire protection engineers believe this to be the case. But research shows the contrary: most people make quite rational decisions in the face of adverse circumstances.
Researchers J.D. Sime and G. Proulx, in studies of a British subway station, refute this myth.1 They call for the provision of good information to maximize evacuation efficiency, believing that emergency procedures should be designed to recognize that people will start to move safely, if given proper instructions in the early stages of a fire.
Additional research by G. Ramachandran suggests that it is stress – often caused by lack of information – which may cause people to act inappropriately in a fire; but rarely do they panic and behave irrationally.2 What's clear is that we can improve the efficiency of evacuation and assist rational decision-making by occupants under fire conditions through measures such as:
- Architecture in which occupants have a clear "cognitive map" or feel for where they are in a building, to aid their movement towards exits;
- Provision of escape paths linked to normal building circulation paths; and
- Use of good signage and clear emergency instructions.
Myth 3: Sprinklers Destroy Property
Another myth prevailing throughout the building management community holds that, if one sprinkler operates in a fire, all sprinklers will "go off" and deliver vast quantities of water, inundating the building and destroying its contents. This notion is especially popular among managers of computer centers, telecommunications facilities, art galleries, museums, libraries and historic buildings.
Fortunately, recognition is increasing that some 90 percent of fires are extinguished by four or fewer sprinklers &endash; and 65 percent by a single sprinkler.
There's also growing acceptance by the arts and historic preservation communities of the notion "better wet than burned." While there's minimal chance of water damage to a building's contents from sprinklers, that risk is preferable to significant or total loss of the building or of a collection, as happened with Hampton Court Palace, Windsor Castle, the Los Angeles Library, the San Diego Space Museum and the Venice Opera House. The rebuilding of several of these buildings without sprinklers, however, suggests the myth about sprinklers is still alive and kicking.
Myth 4: Elevators are Hazardous
Another wide-spread myth maintains that elevators are an area of great fire hazard and should be avoided in fire emergen-cies. But the feasibility of using elevators in a fire has been exam-ined carefully by researchers, and there is even a British standard today specifically for the design of elevators for egress. Fortunately, there's an impulse to re-examine the supposed danger of elevators coming out of the movement to provide equity and better egress provisions for people with disabili-ties. Countries like Australia are examining the needs of citizens with disabilities, with documents such as the Building Access Outcomes Reports by the Australian Building Codes Board appearing in response to the Disability Discrimination Act.
Myth 5: Flashover is Inevitable
Some fire pro-fessionals believe that once a fire starts, it's inevitable it will grow to flashover, breaking all glazed open-ings. But, in fact, research by B.R. Cuzzillo and P.J. Pagni shows that glazed open-ings often do not break, particularly if double or triple glazed.3 This often has the effect of limiting fire growth through ventilation control well before flashover. The effect of glazing in limiting ven-tilation and fire growth was observed in both Australian and British experimental test programs on steel structures. It's also one of the bases of the management practice of removing patients and closing ward doors quickly in hospitals and aged care facilities, to limit fire size, smoke production and smoke spread.
A related myth holds that in large spaces, such as factories and warehouses, flashovers involving all combustibles at peak heat release rate will occur throughout the space. However, G.C. Clifton has demonstrated that flashover as recognized in small compartments does not occur, and that a zone or zones of peak intensity moves through the space over time as the material is consumed.4 The design implication: it is overly conservative to take a total compartment wall area in an industrial building as the radiator for separation distance calculations.
Myth 6: Alarms Sound Before a Fire
Another common myth is that smoke detectors sound an alarm "before the fire starts."
This notion has a magical air, somehow suggesting that certain detectors have intelligence or premonition. If only we could link this capability through "expert systems" to fire prevention programs! We'd save huge amounts of money spent on all the other fire protection systems.
The reality is that some detectors can detect fires in the incipient or smoldering phase, before flames break out. Important here is work by Y. Okayama, T. Ito and T. Sasaki in Japan on the use of neutral nets to detect very early fire signatures.5 Two particular points are worth noting. First, while fire detectors based on optical principles may detect smoldering fires at an earlier stage, other devices (such as ionization detectors) often outperform the optical detectors in flaming fires. Second, in either case, performance depends on fuel type and the particle size and color spectrum of the smoke produced.
Myth 7: Concrete is Invincible, Steel and Timber are Not
A final myth relates to the primary structural materials of steel, concrete and timber.
It's common to think of steel as losing its strength quickly when heat-ed. In fact, single steel elements retain approximately 50 percent of their ambient temperature strengths at 1000 F (550 C). Research shows that due to load redistribution, unprotected steel structural frames may withstand significantly higher temperatures than 1000 F (550 C) with only localized deformation.6 In fact, reinforced concrete loses significant strength above 1400 F (760 C), as illustrated in the SFPE Handbook of Fire Protection Engineering.
Another common notion is that concrete does not lose strength at all in fire – that it's "invincible." However, the loss of the concrete cover in the Channel Tunnel fire is a good example of the failure of concrete through spalling under high fire loads. Exposure of reinforcing due to spalling action can lead to the premature fail-ure of members.
Lastly, the myth persists that timber has no place in structural systems for fire-protected buildings. But, on the con-trary, while timber does burn, it also chars at a well-known rate, and plays a key part as a resilient structural materi-al, particularly in earthquake-prone buildings in New Zealand and Japan. In New Zealand, apartments designed with a "performance-based" approach have been built as high as eight stories with timber framing. Structural element section sizes are designed to char, but still retain sufficient strength to support the buildings after a complete burn-out, or through fire control by sprinklers.
Education is Key
Broad education remains the key to dispelling these and many other popular fire safety myths. The good news is that the number of training opportunities for building designers and the larger construction commu-nity increase every year.
In the post-September 11th era of building design and construction, a "myth-free" environment is sorely needed.
Footnotes
1. Sime, J.D. and Proulx, G., "To Prevent 'Panic' in an Underground Emergency: Why Not Tell People the Truth?," Proceedings of the Third International Symposium of Fire Safety Science, Elsevier, 1991.
2. Ramachandran, G., "Human Behavior in Fires: A Review of Research in the United Kingdom," Fire Technology, 46, 2, 149-155, May 1990.
3. Cuzzillo, B.R. and Pagni, P.J., "Thermal Breakage of Double-Pane Glazing by Fire," Journal of Fire Protection Engineering, 9 (1) , 1988, 1-11.
4. Clifton, G.C., "Fire Models for Large Fire Cells," HERA Report R4-83, New Zealand, March 1996.
5. Okayama, Y., Ito, T. and Sasaki, T., "Design of Neural Net to Detect Early Stage Fire and Evacuation by Using Real Sensors' Data," Proceedings of the Fourth International Symposium of Fire Safety Science, Ottawa, IAFSS, 1994.
6. Robinson, J., Newman G., "Cardington Fire Tests: First Results," New Steel Construction, June/July 1997, 23.
Peter Johnson, CP Eng., is with the global design and engineering firm Arup. Johnson is the leader of Arup's risk consulting business globally. He combines this with his role as the national manager of Arup's fire, risk and security practices in Australasia. He specializes in hazard analysis and quantitative risk assessment, and risk management strategies for project design. These services include strategic, commercial risk advice through to operational risk analysis using quantitative risk assessment (QRA) and reliability analysis techniques.