The potential for residential fire disasters (Figure 1) is of great concern in building design and a significant factor in architectural design of buildings in terms of construction material, configuration, openings and emergency exit strategy. One of the most critical aspects of a building is structural behavior of load-bearing and non-load bearing components under fire and high temperature loading conditions, which can lead to loss of load carrying capacity and thus instability. Providing suitable methods for protection of building components during fires has always been a challenging topic for engineers. Therefore, fire safety systems can play a key role in prevention control or relief of fire before serious damage is incurred to the main components of a building. Needless to say, without proper safety and protection measures, various damage ranges, high repair costs, and even injury or deaths may follow.

As many cities experience shortage of land for more residential and commercial construction due to population growth and migration in modern societies, in particular in metropolitan areas, it is inevitable that building with larger number of stories will be needed, but that will also lead to higher risk of fire hazard. The potential for fire incidents in multi-story apartment buildings remains a serious concern for local governments, municipalities, and building owners/tenants. Karter [1] studied fire losses in the US during 2012 and found that the Fire Departments across the country reported around 1,375,000 fire incidents during that particular year. The Fire Department reports indicate that fire incidents caused over $12 billion property damage, 16,500 injuries and 2855 deaths. Karter study [1] also shows that the risk of fire incidents in residential buildings is much more than other cases such that 83% of fire-related fatalities occurred in homes. As an example of such hazards in overpopulated societies, an official report of China Fire Services shows that about 40% of fire incidents occurred in residential buildings [2] [3] [4] [5] [6] . Because of the expected long life-span of existing buildings, the most reasonable strategy to minimize consequences of fire occurrences seems to be focusing on developing measures for

existing and older buildings in large cities. Moreover, in some cases because modern urban landscape would require long distance transportation of the workforce between home and workplace, some building use changes may be inevitable. These modifications may include the need to have commercial and residential buildings be physically closer and even there may be a need to change the use of buildings, e.g., change the use from commercial to residential or allow mixed use, etc.

These building use changes may trigger and involve required upgrades by building codes. One of the most critical aspects of these upgrades is fire safety, a key aspect of which in these buildings is to ensure that the building’s fire protection systems (if any) function properly. In particular, the traditional fire protection systems require special attention to meet performance standards and code compliance. Creating a comprehensive plan for inspection, testing, and maintenance of these systems can help reduce risk and improve chances of success of the system’s performance. Study of fire safety performance of older buildings in terms of fire spread may lead to selection of different fire safety strategy options [7] , and inspection and maintenance of fire protection devices [8] .

Buildings are usually designed and constructed based on building codes’ fire safety provisions. Such provisions generally provide some standards and the commentaries offer guidelines and concepts for fire alarm and safety such as smoke detector, fire alarm installations, sprinkler systems and fire extinguishers in new buildings. Although new buildings are generally constructed by using more advanced and modern structural and nonstructural systems per building code requirements and industry products, the building contents may not necessarily have been developed and manufactured with consideration of fire safety criteria. This means that because of ever increasing use of modern electronic devices, furniture and various combustible materials and components in buildings, the possibility of fire incidents likely increases [9] [10] [11] [12] [13] . The problem is likely more serious in older dwellings and homes that have amassed large volumes of vulnerable content. Therefore, one of the most significant current problems is fire safety of existing and older buildings since most of these buildings may not fully satisfy the fire safety requirements.

In recent years, engineers have employed some retrofitting methods to reduce the fire hazards. Most studies on fire safety of buildings have focused only on evaluation of new buildings based on fire safety provisions of building codes [14] [15] [16] [17] . With every change of use, change of occupancy, or change of story height, fire protection requirements need to be evaluated. Although retrofit projects have been carried out on fire safety of historical and old buildings [18] [19] , limited information on comparison, advantages and disadvantages of various fire retrofitting systems is available. To have a better understanding of various retrofitting methods, there is a need for a thorough review of literature related to fire hazards. Such a study can then lead to evaluation of various options and determining appropriateness of solutions for different situations.

One of the most significant current discussions in mitigation of fire hazards is retrofit of existing buildings. For instance, when changes are to be made in a building, usually upgrading or adding fire protection systems will also be part of the change. In this regard, to find the most suitable retrofitting method, learning from past fire incidents in similar buildings will be useful. This section reviews some example reported fire incidents to help better understanding of the common causes of fire spread in the existing buildings. Generally, any proposed method for retrofitting existing buildings should be based on a sound understanding of causes of fire incidents and its spread. For example, on May 22, 2010, a fire incident was reported to the US. Fire Administration office in Kansas [20] . An automatic fire alarm was received at 20:52 from the residence. The incident involved a 6000 square foot two-story single-family residence with a full-base- ment that was built in 1998. The lower level included a walk-out basement (Figure 2). The main floor consisted of a great room, dining room, kitchen, breakfast room, master bedroom and bath with make-up room, utility room, office and a two car garage. The top floor consisted of three bedrooms and two full bath-rooms. After the fire incident, the office of the State Fire Marshal reported that the building was not equipped with a proper fire sprinkler system. The firefighting time table in Figure 2 shows that despite a quick automatic fire alarm, lack of an adequate fire sprinkler system can lead to a significant damage to the whole building.

As a second example, one can cite the fire incident reported on March 8, 2015 when a Danville man escaped unharmed from a fire that destroyed his home in the evening [McGee 2015, News-Gazette 4/28/2015]. Firefighters were called to a house fire around 6 p.m. When they arrived, heavy fire and smoke was coming from the front of the small, one-story, wood-frame structure. The report shows that the house occupant was asleep on his couch when the fire broke out, but was awakened by the smell of smoke to see his kitchen was on fire. He was not injured and firefighters extinguished the fire in about 20 minutes. According to the firefighters, the fire caused the front of the house and roof to cave in, which caused an estimated $25,000 damage. This report indicates that there was no fire extinguisher and alarm system at the home, and the occupant was awakened by the smell of the smoke. Perhaps, if there was a smoke detector or fire alarm, the occupant could wake up sooner. Also, the existence of a fire extinguisher system such as fire blanket and sprinkler in the kitchen could help extinguishing the fire or to prevent its spread.

A fire incident was reported in a residential building in Peekskill-Cortland, NY that was extinguished by the assistance of Lake Mohegan Volunteer Fire Association [21] . The report shows that this building was not equipped with an adequate fire safety system. Despite key role of the fire alarm and fire sprinkler systems in fire incidents, the use of fireproof materials and components is always a reliable strategy to protect against or delay fast fire spread to other places in a building. The report indicates that unprotected openings in the building envelope

caused the fire to spread. In such an incident, the use of fireproofing curtains or paints [22] [23] could prevent or slow down the spread of fire to roof and other areas of the building. The report shows unprotected openings in the building envelope caused the fire to spread. In such an incident, the use of fireproofing curtains or paints [22] [23] could prevent or slow down the spread of fire to roof and other areas of the building. In another fire incident, it was reported that the building envelope was damaged during a fire. This building was equipped with fire alarm system, which alerted the residents in a timely fashion thus leading to safe evacuation of the building. The home did have working smoke detectors. The fire department’s quick response enabled firefighters to contain the fire just to the back of the structure and prevented further damage to the home. In this case, the use of fireproof paints [24] could have prevented or minimized further damage of building envelope.

One of the most significant current problems in fire safety of existing residential buildings is fire spread from openings (e.g., holes) and cracks in the walls. When a fire incident occurs, the generated flames tend to spread to other places where there is more oxygen. Therefore, the existing openings and cracks in the walls can encourage and help spread of the flames. Figure 3 shows a fire spread test on a wall with two different cover boxes for wall plug [25] . In this test, the left box was made of plastic and the right box was made of fireproof material. As Figure 3 shows, when the wall was exposed to fire, the left box melted and the flames could spread to the front side of the wall. On the other hand, the right box did not burn and blocked the fire spread.

Fire sprinklers systems using water are one of the most widely used fire extinguisher systems in residential buildings. The experience of residential fires has indicated that the fire sprinklers have acceptable performance to help life safety in such high temperature incidents [26] . Figure 4 shows a fire sprinkler head that is activated onfire. In this test, the sprinkler was indeed able to control the flames and to provide enough time for firefighters to arrive at the scene to extinguish the fire.

To further help better understanding of causes of typical fire incidents and their spread, a summary of several cases is included in Table 1, which shows an overview of five different reports about fire incidents in residential buildings. It is apparent from the table that most of the buildings reported have not been equipped with proper fire safety systems. The information in the table shows that the spread of fire and smoke from fire-source to other places is the main cause of increase in injury and damage in fire incidents. The most interesting point of the reports is that although using fire alarm device can play a vital role for safety of occupants, such devices need a complementary fire protection system.

Fire hazard has always been a significant concern for building safety in comparison with other disasters (e.g., natural hazards). Although earthquakes and hurricanes as examples of more frequent natural hazards can turn to disasters for buildings, their frequency of occurrence and intensity levels depend on the regions

where buildings are located. However, records of past fire incidents show that fire accidents may occur in any region and any building type, although more frequent in residential buildings [28] [29] . Therefore, if fire safety measures are not appropriately considered in design and maintenance of buildings, the result could be increased risk of building damage and tragedy. Performance of buildings has shown [30] [31] [32] that actual structural stiffness of buildings with structural steel framing members will be reduced due to fire, which will also affect load bearing capacity of heated members. The softening of structural members under heat can compromise the stability of whole building. Studies [33] - [39] have also found that during a fire, elevated temperature of members exposed to fire can induce large axial forces in restrained structural members due to thermal expansion. This phenomenon is thought to be the main cause of early building collapse during a fire.

For many years, the use of fire protection systems in buildings has been undervalued and largely misunderstood [16] . This was first realized when a number of real fires occurred in buildings. As one of the pioneers in fire research, John Carey designed a perforated pipe concept for fire protection systems in 1806 [40] . Three years later in 1809, William Cosgrove of London patented an improvement to the system that used 190˚F rated fusible link actuators, an outside control valve, and a fire department connection [40] . Before 1990, fire safety projects dealing with thermal resistance of buildings mainly focused on manual systems such as fire hose reels, fire buckets and manual foam fire extinguishers. In more recent years, there has been an increasing interest in designing practical protection systems against fire. Some of these design methods recommend traditional protection systems for materials and devices, which vary depending on safety, size and economic justification of projects. The protection methods are divided into three sub-categories: 1) protection by mechanical systems such as fire sprinklers, 2) chemical flame retardants such as coating or isolating members by the use of fire resistance coating material and 3) structural mass resistance such as increase in size of members’ sections or embedding members in concrete.

When an existing building is considered for (other than fire) upgrade changes, it is also advisable to consider possibility of adding new fire protection systems to satisfy new fire code requirements. Retrofit design of an existing building begins

with a primary evaluation of current fire protection system. After the evaluation process, review of various fire protection systems appropriate for the building and fire codes is carried out and some options identified. Finally, from the list of viable alternatives, one or combination of protection systems are selected based on the budget and level of fire hazard protection required for the project. Advantages of fire retrofitting of existing buildings with deficient fire-safety systems include: 1) building code compliance, 2) decrease in potential fire-related damage and losses, 3) flexibility for changes in building, 4) improved life safety and 5) reduced property insurance premiums. Figure 13 shows a flowchart identifying various stages of retrofitting an existing residential building against fire. As the flowchart indicates, each building needs to be inspected in terms of fire safety criteria. The primary inspection can be separately carried out on structural and non-structural components. For designing an adequate retrofitting plan in residential buildings, three stages should be considered. In the first step, the potential fire areas such as mechanical room and kitchen should be identified to inspect fire extinguisher systems. In the second stage, the existing cracks and holes on the walls, floor and roof should be marked and filled by a proper fireproof (firestop) material. The aim of this stage is to separate and protect important spaces against fire spread. Therefore, in some cases the use of fireproof elements such as fireproof curtains and doors may be necessary to separate escape routes from other areas. In the last stage, the potential smoke and fire areas should be identified for installation smoke detectors and fire alarms. Figure 14 shows various alternatives for fire extinguisher systems, fire alarms devices, and fire stop materials. By use of the proposed flowcharts in Figure 13 and Figure 14, we can find an adequate retrofitting design for existing residential buildings to equip them against any probable fire incidents.

A representative sample of relevant literature concerning fire incidents in buildings was reviewed to identify the main causes of fire spread in existing residential buildings. As older residential buildings constitute a considerable portion of existing residential building stock, and normally such buildings are more fire-safety deficient compared to newer buildings that have been constructed following more recent building codes, it is clear that a large number of such buildings need to be retrofitted to upgrade for an adequate fire safety system to satisfy the new fire codes. Review of the traditional and new retrofitting methods for fire safety of buildings in this report provides an overview of the technologies available. Information gathered from multiple sources and a variety of old and recent high-tech fire protection and retrofitting systems presented offer a state-of-the-art review of viable approaches that can be adopted for fire retrofit projects, including some of the advantages and disadvantages of fire protection devices and strategies.

Comparison of various features and attributes of different fire safety systems shows that each option has some strength and also some drawbacks. One can then conclude that the disadvantages of a solitary system for fire-retrofitting can be improved by using combination of several fire safety methods simultaneously. An important finding from this study is that proper inspection of fire alarm, fire extinguisher and fire spread control systems is a critical step in fire safety evaluation of an existing building that is considered for possible fire retrofitting.

Zahmatkesh, F. and Memari, A.M. (2017) Review of Conventional and Innovative Technologies for Fire Retrofitting of Existing Buildings. Open Journal of Civil Engineering, 7, 222-244. https://doi.org/10.4236/ojce.2017.72014