Fire Risks in High-Rise Buildings

By: Dr. Ankit Sharma, Case Western Reserve University (CWRU), USA.

Fire is essential in our daily life but can be disastrous when it becomes out of control. The reasons for the fire are either human-made or natural, and the result is a considerable loss in terms of life, property, and environment. As per the World Health Organization Report 2014, fire causes 5% of injury-related deaths worldwide while war causes 2%. Fires in structures and high-rise buildings constitute a significant portion of fire accidents. In the US during 2009-2013, there was an average of 14,500 structure fires per year in high-rise buildings causing numerous casualties and $154 million in loss of property per year.

In recent years, record high-rise buildings have been constructed (Fig. 1), and many more are in progress. These buildings are also called “vertical cities” as many occupants eat, sleep, live and work in them. In India, a building greater than 23m (generally 7 to 10 stories), is considered high-rise while in UK and USA, height criteria are greater than 30m and 22m, respectively. Until now, the tallest structure ever built is Burj Khalifa having an astonishing height of 828m. The pace with which the demand for these buildings is increasing and this record may be overridden soon. This outburst has urged engineers and researchers worldwide to devise fire safety measures.

The associated fire risks of the high-rise residential building usually include:

• Rapid external and internal spread of fire and smoke
• Difficult firefighting and rescue
• Difficult safe evacuation of the occupants
• Fire lasting for a longer time
• Stairwell filling with smoke

Previous fire incidences (Fig. 2) in high-rise buildings have shown that although the regulatory bodies have set norms and safety measures in the form of codes, their practical implementation and regular monitoring need improvement.

There is a need to revive the existing codes and regulations to meet the ever-increasing demand for modern urban infrastructures. Every building is unique in terms of fire load, usage, occupant characteristics, and requirements. Following similar building codes for all buildings may lead to over-safe or under-safe design and limit flexibility. This has led to the development of Performance Based Design (PBD). PBD approach designs the building considering different aspects ranging from energy consumption and reducing operating costs to occupant’s comfort and safety and decreasing environmental impact.

The excessive usage of combustible items in modern-day infrastructures like doors, windows and furniture combined with the lack of sprinklers and fire alarms, is also one of the major reasons for frequent fire accidents resulting in internal fires and smoke spreading inside the building including stair-well. Depending upon the ventilation and flashover conditions, these internal fires may come out from the compartment leading to external wall fires. The severity of these external fires increases manifolds if the exterior wall assembly is composed of flammable materials or has construction features like air cavities or sidewalls, which further escalate external fire spread (Fig. 3).

Therefore, it is necessary to understand the involved physics in fire and smoke spread in high-rise buildings. Undoubtedly, such fires cannot be reconstructed physically due to the large scale involved. Therefore, the only way to investigate these fires is by performing experiments at a lab scale with boundary conditions similar to the real scenarios or performing numerical simulations, using Computational Fluid Dynamics (CFD) codes.

RECENT RESEARCH

A recent experimental investigation by the author [Sharma and Mishra 2021] has studied the influence of the ‘chimneyeffect’ on the fire response of rainscreen façades (Figure 4). The novel experimental setup is developed to predict the burning behaviour of façade materials at the lab scale [Sharma and Mishra 2020, Indian Patent]. Results illustrated the significant role of the chimney effect in enhancing the vertical fire spread on the rainscreen façade system. A critical range of cavity width (13 to 50 mm) was established for the investigated configuration between which maximum fire spread and structure failures were observed. Further research is needed to find out the critical widths of the air cavity for different configurations. Numerical modelling of the developed experimental setup was also done that discussed the capability of numerical tools like Fire Dynamics Simulator (FDS) in predicting vertical fire spread and assessment of full-scale façade fire risks Fig. 4 [Sharma 2021].

Fire protection is of utmost importance in the built environment and should be integrated with the overall building design. To achieve the highest level of fire safety, both fire protection engineers and architects must work together using a prescriptive and performance-based design approach. Especially in high-rise buildings, façade and fenestration design must go hand in hand as both in conjunction are responsible for fire spread to other parts of the building via exterior combustible cladding.

Note: The views and opinions expressed in this article are those of the author and are not linked to any agency, organisation, employer, or company.

REFERENCES
1. Ankit Sharma, Kirti Bhushan Mishra, “Experimental investigations on the influence of ‘chimney-effect’ on fire response of rainscreen façades in high-rise buildings”, Journal of Building Engineering, Volume 44, 2021 https:// doi.org/10.1016/j.jobe.2021.103257

2. Ankit Sharma “Experimental and numerical investigations on external and internal fire spread in high-rise buildings” PhD Thesis, Indian Institute of Technology (IIT) Roorkee, 2021

3. Ankit Sharma, Kirti Bhushan Mishra, Indian Patent: Method and apparatus for testing fire behaviour of façade materials IN202011010546.