Study on the Development of Multi-Purpose Fire Engines through Vehicle Safety Factor Design

1.1 Background and purpose for development of multi-purpose ladder-fitted fire engines

Densely populated areas are increasing as vast numbers of people converge on city centers, with consequent limitations on residential space and industrial facilities. To resolve these problems, the construction of structures such as multi-family houses and high-rise apartment complexes has steadily increased to allow a greater number of people to reside in a limited space[1].

High-rise buildings[2,3] provide numerous convenient facilities, but fires at such structures can lead to large-scale accidents that cause devastating losses of life and property. As preventive measures, the criteria for firefighting facilities have been reinforced, and high-ladder fire engines to allow fire suppression on higher floors are purchased each year to prepare for accidents[4,5].

The preventive measures for high-rise buildings and newly built structures are reinforced each year. While numerous improvements have been made regarding firefighting facilities and devices supplied to fire stations, there is a general lack of fire-prevention measures for low to mid-rise residential complexes and industrial facilities constructed in the past. Despite numerous improvements in fire defense regulations, fire and disaster measure reinforcement, and advances in firefighting devices, the level of fire incidence in residential areas has not been reduced, as shown in Table 1.

Table 1

Current Status of Fire Incidence in Residential and Commercial Districts by Year

The steady level of fire incidence despite many efforts and high costs to ensure the safety of newly constructed or high-rise buildings is due to the fact that fires most frequently occur in old, decrepit buildings and multi-family houses with inadequate firefighting facilities and legal regulations.

The reasons for the high levels of fire incidence and loss of life in such densely populated areas as old buildings and multi-family houses[6] are as follows. First, the legal restrictions on construction at the time were inadequate, and second, the construction was not in accordance with planned roads. Hence, despite the advanced devices and fire engines that are presently available, fire suppression and lifesaving at these structures still pose numerous challenges.

It is critical that firefighters arrive at the scene of a fire or disaster that requires lifesaving efforts within the golden time to perform these duties. However, the biggest challenge upon arrival at a fire scene is actually narrow roads and illegally parked cars, rather than the fire itself. This is because the currently supplied ladder-fitted fire engines and articulating ladder vehicles with a high-rise ladder fitted to a large vehicle (≥10m in full length) demand a large space (5.2 m) for the outrigger to be extended for fire suppression and lifesaving[7,8]. In addition, the control of such devices is difficult and complex in the absence of a skilled engineer, while much time is required to arrive at the fire scene and perform these duties even if the operation is possible.

In December 2017, a fire occurred at a sports center in Jecheon[9]. This fire started on a floor below the sports center, and as a result of the characteristic piloti structure, the empty space on the first floor served as a passage that supplied oxygen, which allowed the fire to rapidly grow into a large-scale fire. Although pump engines and water tanks arrived at the scene and prepared for fire suppression, the ladder-fitted fire engine could not reach the scene because of cars parked illegally in a narrow alleyway. In the meantime, people in the upper part of the building could only wait for the ladder to arrive as they hung on the guardrails. Figure 1 shows the scene of the Jecheon fire.

Figure 1

CCTV footage at the time of the Jecheon fire.

The delay in the arrival of the ladder-fitted fire engine due to the cars parked at the entry made early fire suppression and lifesaving in the upper part of the building very difficult. A tower wagon from a private company called a Skycar [10] was able to rapidly rescue the people hanging onto the guardrails because of its small size and fast mobility. The Skycar could respond more swiftly than the ladder-fitted fire engine because its small size allowed it to easily enter through the alleyway, while the basket on the top part of the vehicle allowed the easy rescue of people even though the vehicle was being controlled by an ordinary citizen.

Ladder-fitted fire engines are currently stationed only at the main fire stations in the critical regions of each district. Because of its high cost, a ladder-fitted fire engine is one of the most difficult items for a fire station to purchase. Even if large purchases could be made through the establishment of an appropriate budget, the large vehicle size is likely to prevent rapid responses in situations like the Jecheon fire.

Providing each fire station with a small ladder-fitted vehicle with just a ladder function as a tower wagon would entail various problems such as the execution of a budget solely for the respective operation and the employment of engineers who can run such vehicles. In addition, there are bound to be complaints about wasted money because of the reduced operating efficiency if such vehicles only provide a simple ladder function. Thus, the R&D of multi-purpose fire engines with an additional ladder function based on the midsized pump engines that are commonly used at fire stations would efficiently reflect the demands in the field.

Midsized pump engines[11] are the most basic type of fire engine and the most commonly used vehicles at fire stations. If these engines could be given an additional ladder function, the resulting multi-purpose engines would substitute for conventional engines and prevent the need for more engineers or garages. In addition, because they would be the main dispatch vehicles, the efficiency would also be outstanding. The significantly reduced full length and operation width compared to conventional ladder-fitted fire engines would allow the same easy entry through alleyways next to multi-family houses as the pump engines. Thus, they could arrive at the fire scene within the golden time for simultaneously performing fire suppression and lifesaving operations.

1.2 Overview of the product to be developed

When a fire occurs in a densely populated area or industrial district, the method to minimize the loss of life and property is to ensure a rapid response within the golden time. Therefore, this study investigated the development of fire engines that would allow fire suppression and lifesaving in the given circumstances. A way to resolve the problems of conventional fire engines is also suggested, which would contribute to the development of new fire engines. Above all, the problems of the currently used large ladder-fitted fire engines can be summarized as follows. First, the fire suppression and lifesaving functions are separated and require separate vehicles. Second, it is difficult for large ladder-fitted fire engines to reach the common residential or commercial complexes. Third, a large space is required for a large ladder-fitted fire engine to allow its wide outriggers to extend. Fourth, it is difficult for all fire stations to purchase and maintain large ladder-fitted fire engines. Fifth, the control and operation of a ladder-fitted fire engine require an expert engineer or the operation is difficult. Thus, the following R&D directions for multipurpose fire engines were considered. First, the structure should be designed to allow fire suppression and lifesaving to be performed simultaneously. Second, the base should be a 5-ton chassis (i.e., a midsized pump engine). Third, the ladder should be designed to reach the full height of low to mid-rise buildings. Fourth, through simple operation, the system should allow a single operator to extend the ladder and release the water. Fifth, a waterproof canvas basket should be installed at the end of the ladder.

1.2.1 Relevant technological trends in South Korea and overseas

With the advancement of technology by professional manufacturers of fire engines both in South Korea and overseas, the main focus is on the maximum height of fire suppression by ladder-fitted fire engines. However, for old buildings with inadequate firefighting facilities, the suggested alternative measures remain incomplete. Thus, a fire inevitably causes a serious loss of life and property in a case where early suppression fails. This is not just a problem in South Korea. At the 2018 Firehouse Exposition in Tokyo, a company called Morita in Japan exhibited a vehicle with a boom structure similar to the one suggested in this study, as shown in Figure 2. In Japan, as an advanced country in relation to firefighting, cities have structures similar to those in South Korea, with a concentration of residential and commercial complexes. The fact that a Japanese manufacturer of fire engines has designed a vehicle with a form similar to that investigated in this study implies that the same problems exist in Japan.

Figure 2

Product exhibited at the 2018 firehouse exposition in Tokyo (Morita).

However, this newly developed Japanese vehicle had a very small water tank at a level equivalent to the small pump engines in South Korea. The addition of the ladder function to a conventional pump engine appears to have necessitated a reduction in the water tank volume as a result of loading space and related issues. The ladder height was only 13 m, preventing fire suppression and lifesaving above the 3^rd or 4^th floors, which was another drawback of the design.

Because efforts are being made in Japan toward the development of fire engines similar to the one investigated in this study, it is predicted that the completion of the R&D proposed in this study will advance the engine development in Japan with respect to its functions, performance, and economic feasibility, and thus lead the fire engine trend in Asia.

2.1 R&D goals

While the high-rise buildings being constructed at present should comply with the requirements for modernized firefighting facilities and fire engine accessibility based on the Building Act, low to mid-rise apartments, houses, and shops are being constructed with inadequate consideration given to firefighting requirements because of the relaxed regulations of the Building Act. Notably, these structures are widely distributed across residential areas, which shows the potential for serious damage in a fire incident. The conventional ladder-fitted fire engines at each fire station are specialized for high floors. However, it is difficult for them to reach a fire scene through narrow alleyways and complex road conditions. Then, even upon successful entry, a challenge remains because the outrigger extension demands a sufficiently wide space. Thus, it is very important to develop fire engines to resolve such problems, and preserve the lives and property of citizens.

The purpose of the R&D conducted in this study was the development of a multi-purpose fire engine that can serve as a pump engine and be rapidly dispatched to a scene involving low-floors (2^nd–6^th) for fire suppression or lifesaving. It was based on the 5-ton commercial chassis of a conventional midsized pump engine. Its novel design combines pump and ladder functions. Thus, a different approach was required compared to the widely distributed conventional ladder-fitted fire engines. At its completion after significant time and effort involving numerical calculations of the respective vehicle component designs, this novel multi-purpose fire engine will make a huge contribution to the protection of precious life and property in South Korea.

The outcome of the proposed R&D will also provide reliable basic data, because the design could be applied to other vehicle types. Fire engines broadly include pump engines, water tanks, chemical tanks, rescue vehicles, and ladder-fitted fire engines, and the successful combination of pump engines with a ladder function is thus likely to be applicable to other vehicle types in time.

2.2 R&D performance indicators

For the R&D in this study, eight performance indicators were set. The maximum load of the basket was set to ≥250 kg to withstand the combined weight of three or more adult men, with the load cell and safety devices fitted accordingly. A low maximum load for the basket would limit the lifesaving process, whereas if the value was too high, the chassis could exceed its limit when the ladder was elevated to the maximum height or moved horizontally. Hence, the maximum load was set to 250 kg. The control device was designed to allow easy access by anyone and programmed to allow both wired and wireless control. Conventional ladder trucks can only be controlled by the assigned engineer, who has to be in proximity to the ladder, which makes it difficult to understand the changing circumstances at the scene and can cause secondary accidents. In contrast, this novel design allows ladder movements to be controlled using a wireless joystick.

A load cell fitted to the basket allows the load on the basket to be monitored in real time, and because this presents the engineer with quantitative values rather than just an alarm, it enhances their judgments. In addition, alarm devices to detect the approach of an object are fitted to either side of the basket, and the basket movements are limited when one of these sensors perceives that an object is within 500 mm of the left or right side.

The operation scope of the ladder truck can vary according to the load on the basket. Hence, based on the design calculations, the movements of the fire engine should be limited when the load exceeds the permitted range, which enhances the safety. Basic tests on the boom operation speed, settlement, and overturning were performed in a fundamental evaluation for safety certification. Table 2 presents the evaluation criteria for the R&D in this study.

Table 2

Evaluation Criteria for the Project to Develop Multi-Purpose Fire Engines

3.1 Basic design and related principles

The safety factor is a design parameter used to prevent an imbalance across materials when a load higher than the load limit is applied, there is heterogeneity in the product quality during production, weakening occurs as a result of abrasion or corrosion during use, or there is uncertainty regarding the reliability of the data. It is obtained by dividing the level of safety a structure can maintain (i.e., the fracture strength) by the allowable capacity.

Figure 3 shows a design that reflects the safety factors of three booms and boom cylinders of a ladder-fitted fire engine to estimate the safety factor for the structure when unfolding the ladder.

Figure 3

Structure of multi-purpose fire engine with three booms and boom cylinders.

Here, the safety factor is S=σu(ultimate stress)σω(working stress), while the working stress is the stress that allows a structure to be used safely without a permanent change, and the ultimate stress is the maximum stress or tensile strength =maximum loadinitial area. The relationship between the two stress types is σw≤σa≤σuS. In other words, the relationship is as follows: working stress≤ultimate stresssafety facctor≤proportional limit≤yield stress≤ultimate stress.

Figure 4 shows a first-tier boom, and the process of estimating the tensile and compression safety factors is given in Table 3. It should be noted that, for the first-tier boom, the center of weight and cross-sectional secondary moment are Yt=∑(A×e)∑A=174 mm and Iy=b×h31296,389,595 mm4, respectively.

Figure 4

Size and length of the first tier boom (unit: mm).

Table 3

Estimation of Tensile Safety Factor and Compression Safety Factor for the First-Tier Boom

Figure 5 shows a second-tier boom, and the process of estimating the tensile and compression safety factors is given in Table 4. It should be noted that, for the second-tier boom, the center of weight and cross-sectional secondary moment are Yt=∑(A×e)∑A=152 mm and Iy=b×h31245,617,955.23 mm4, respectively.

Figure 5

Size and length of the second tier boom (unit: mm).

Table 4

Estimation of Tensile Safety Factor and Compression Safety Factor for the Second-Tier Boom

Figure 6 shows a third-tier boom, and the process of estimating the tensile and compression safety factors is given in Table 5. It should be noted that, for the third-tier boom, the center of weight and cross-sectional secondary moment are Yt=∑(A×e)∑A=131.3 mm and Iy=b×h3122,8887,201.35 mm4, respectively.

Figure 6

Size and length of the third tier boom (unit: mm).

Table 5

Estimation of Tensile Safety Factor and Compression Safety Factor for the Third-Tier Boom

In addition, the process of estimating the boom cylinder safety factor in consideration of the load, as illustrated in Figure 7, is described as follows. Table 6 lists the maximum load and buckling constant for each boom.

Figure 7

Size and length of boom cylinder (unit: mm).

Table 6

Load and Buckling Constant of the Boom Cylinder

Based on the following: F = load on the chain × (2) + W3 = (575 × 2) + 370 = 1520 kg, fixed distance at maximum pull L = 4,950 mm (closed length + stroke (4,800 mm)), D = 80 mm, road = (d1: 50 mm, d2: 30 mm), N = buckling constant, E = Young’s modulus (2.1 × 10⁶), I =(π×(5⁴–3⁴))÷ 64 =26.70 cm⁴-, buckling load (Pb) = (N × π² × 2100000 × 26.70 ÷ 495² = 9070.61 kgf, the safety factor (S) is Pb/F = 9070.61/1520 = 5.97.

As can be seen, each load factor for the ladder fitting to each midsized pump engine was calculated for the design to estimate the final result values for the product design. Table 7 lists the specifications for the final product.

Table 7

Specifications for the Multi-Purpose Ladder Truck

3.2 Multi-purpose fire engine: A 3D design

Based on the 5-ton fire engines most commonly applied in the R&D of multi-purpose fire engines, a ladder function could be added to a conventional fire engine, with a maximum ladder height of 20m for a design that would enable fire suppression and lifesaving operations. The end of the ladder is shaped like a basket to ensure the safe boarding of firefighters for fire suppression and lifesaving operations. The outrigger design allows a vertical descent to allow ladder work to be performed as long as vehicle entry is possible despite illegally parked cars.

This study developed a novel design for a multi-purpose fire engine that would be suitable for practical application in South Korea. The National Fire Agency, as well as relevant administrative bodies and private companies, have expressed interest in such fire engines. Thus, it is anticipated that newly purchased and alternative fire engines will be fitted with a pump and ladder. Figure 8 depicts the 3D design of the multi-purpose fire engine with a ladder to be developed based on this study.

Figure 8

3D design of multi-purpose fire engine.