1 Introduction

Passive fire protection (PFP) materials are used for the fire protection of steel structural members, and other assemblies such as equipment, vessels, pipe, valves, etc. In case of fire, they should restrict the temperature rise below the critical point where these units stop functioning [1]. Different types of passive fire protection materials in various forms are used for fire protection. The types of material used can be classified as cementitious, ceramic fibres, mineral wool, vermiculite, perlite, intumescent, sublimating, and ablative materials [2, 3]. These materials can be applied in form of boards, spray, coating, and encasing depending on the site requirements.

During their functional life, these passive fire protection materials may be exposed to different types of fire conditions depending on the location [4]. To achieve the desired fire performance, it is essential to design and provide the required thickness of material to restrict the temperature rise below the critical value and achieve desired fire-resisting rating [5]. The thickness requirement of passive fire protection depends on the type of fire, duration of fire exposure, critical temperature, and the ratio of exposed area to volume. Fire resistance tests are carried out to determine the fire resistance rating by exposing the specimen to a standard test [6]. The duration of fire exposure, where the specimen will withstand concerning performance criteria is called fire resistance ratings. For certain building elements, the performance requirements are to maintain structural integrity as in the case of columns while, for walls, floors, ceilings, and other assemblies they should also prevent transmission of heat/spread of fire [6, 7]. Fire resistance requirements, which are specified in different codes, are based on tests conducted with types of fire i.e., standard fire (ISO 834 [8], ASTM E119 [9]), hydrocarbon fire (ASTM E1529 [10], UL1709 [11]), RWS fire and jet fires (ISO 22899-1) [12].

Broadly the non-metallic PFP materials can be categorized as inorganic type and organic type.

The composition of organic formulation as a protective coating or barrier contains the functional ingredients such as binders, plasticizers, non-combustible inert fillers, carbonic agents, blowing agents, and sublimating agents. All organic materials, produce char after burning at a certain temperature. In modern days, organic material in polymeric form is widely used by polymer-based companies to produce specific products according to the need of customers [13]. Poly-composites and poly-alloy composites, can fight fire scenarios ranging from a regular fire to a jet fire scenario [14]. The basic reason behind such a wide variety of characteristics is that poly-composite can be formulated to incorporate, intumescent, ablative, and sublimation properties. Reinforcement containing steel fiber, carbon fiber, glass fiber, ceramic fiber, etc., makes the polymeric PFP products useful for even semi load-bearing utility structures. By using such a wide range of materials the high fire-rated components can be manufactured for the domestic building industry as well as utility structural components of industrial, marine, ships and submarines and other critical closed vessels. Inherent polymeric material properties like low thermal conductivity, or a wide range of flexibility, and compatibility with various material is definitely useful to complement the disadvantage of basic structural load-bearing properties as compared to steel and Reinforced Cement Concrete (RCC).

Inorganic materials are offered as pre-formed boards, sprays, and coatings. Non-combustible inorganic fillers of natural mine origin are utilized to include fillers' built-in fire-resistant qualities [15]. Binders made of silicon are frequently used to provide strength. Additionally, they might be reinforced with mineral fibers or without reinforcement (inorganic polymeric materials). From this perspective, inorganic polymeric materials seem promising. They are non-combustible and offer superior mechanical, thermal, chemical, and physical characteristics along with low production costs and significant environmental advantages.

The objective of this study was to investigate the behavior of organic and inorganic passive fire protection materials in different types of fire exposure when used for the fire protection of steel structures. Experiments were carried out to study the behavior of the same material under standard, hydrocarbon, and jet fire exposure conditions. The performance of protection material is assessed concerning the mode of heating, heating rate, peak temperature, and erosive effect. The results have been reported and analyzed in terms of changes in physical properties and thermal performance. The necessity of this study is to give ideas/direction to the manufacturers/researchers/designers who are developing/implementing the various PFP material on critical installations, where these scenarios should be considered to achieve desired fire performance.

2 Properties of Passive Fire Protection Material

Two types of materials one organic with inorganic filler and the other inorganic were selected for carrying out the experimental work. The detailed properties of both organic and inorganic materials are given in Table 1.

Table 1 Properties of Passive Fire Protection Materials Used for the Protection of Steel
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3 Specimen Preparation

3.1 Specimen for Standard and Hydrocarbon Fire Exposure

To study the behavior of organic and inorganic fire protection material, specimens were prepared by protecting the steel substrate with a predetermined thickness of the material. For standard and hydrocarbon fire exposure conditions rolled steel I sections of dimension 125 mm width and 200 mm depth were taken, refer to Figure 1a. Before the application of protection material, for both steel specimens, I-sections surface preparation was carried out as per SSPC SA 2 ½ [28] to remove the undesired materials from the steel surface. The thermocouples were fixed to the surface of the steel to measure the temperature on the steel surface, as illustrated in Figures. 1b, c. Furthermore, these I sections were protected by applying organic and inorganic materials. However, for both cases, a thickness of 22 mm was applied to the steel surface. The details of the specimens are shown in Figure 1a. The entire built-up thickness of the protection coating was achieved by applying the material in layers. The thickness of each layer was kept at approximately 7–8 mm. After the application of each layer, it was allowed to dry for 8–12 h before the application of the next layer of protection material. The specimens were prepared in a covered shed in ambient atmospheric conditions. The variation in temperature in the shed during the period of preparation of the specimen was 24°C to 30°C and the humidity varied from 76% to 80%.

Figure 1
figure 1

Details of Specimen for Standard Fire and Hydrocarbon Fire Exposure (a) Position of thermocouple and sectional dimensions of I-Section (b) I-Section with organic Coating. (c) I-Section with inorganic Coating.

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3.2 Specimen for Jet Fire Exposure (ISO 22899-1)

A plate, 1620 mm wide and 1570 mm height formed the rear wall of the test specimen and provided 60 mm wide flanges around the three sides of the specimen. Thirteen holes of 18 mm diameter were drilled in the flanges at the centerline at different spacing as illustrated in Figure 2. Three lifting lugs were connected to the top of the plate for ease of handling of the specimen. The rear wall of the test specimen was made of 10 mm thick steel. The web comprises two steel plates of 10 mm thickness, which were slotted before being welded together, to have thermocouples inserted and fixed. Holes were drilled in the rear wall of the specimen to match the slot positions. Details of the construction of the web are given in Figure 2c. The central web of the specimen was made by welding together two plates that were 1500 mm high, 250 mm wide, and 10 mm thick. Five grooves were cut into one plate so that the K-Type (6 mm Diameter- Chromel/Alumel) could be put between two steel plate. The grooves were made 187.5 mm, 375 mm, 562.5 mm, 750 mm, and 1125 mm from the bottom of the test specimen. Ball nose cutters were used to cut the slots in the plate.

Figure 2
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Details of Specimen for Jet Fire Exposure (a) Steel specimen coated with inorganic material (b) Steel specimen coated with organic material. (c) Sectional dimensions for the central web and thermocouple location in the web.

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The PFP material i.e., organic and inorganic material was applied on all the inside surfaces of the specimen with 22 mm of thickness. The built-up thickness for the material and specimen installed in the re-circulation and protective chamber is depicted in Figure 2a, b.

4 Experimental Set-Up

A set of experiments were carried out under standard fire, hydrocarbon fire, and jet fire exposure conditions.

4.1 Standard Fire and Hydrocarbon Fire

For standard fire and hydrocarbon fire exposure vertical fire resistance test furnace as shown in Figure 3a, b is used. The design specification of this furnace is given below in Table 2:

Figure 3
figure 3

(a) Actual photograph of Vertical Resistant Furnace Test (VFRT) furnace. (b) 3-dimensional model of Vertical Resistant Furnace Test (VFRT).

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Table 2 Design Specification of the Vertical Fire Resistance Test (VFRT) Furnace
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All the readings were recorded with programmable logic controller (PLC) and supervisory control and data acquisition (SCADA) system. These systems can control all furnace functions, data log, and all instrumentation readings and display real-time information on the test duration (in minutes), the temperature of burners (°C), mean furnace temperature (with upper and lower limit), real-time furnace pressure (Pa), real-time values of the percentage deviation and areas under the time–temperature heating curve (°C) and individual reading of specimen temperature

The furnace body is mainly made of mild steel plates and steel channel sections. All the furnace walls i.e., side, top and bottom walls are composited with a combination of insulating fire bricks, alumina fireboards, and calcium silicate boards. To record the temperature inside the furnace during the test, total number of 16 K-type thermocouples were inserted from the rear wall of the furnace with an 8 mm steel pipe casing. A total of 16 burners are evenly spaced on the rear wall of the test furnace with an automatic combustion air blower to achieve the desired heating conditions. In addition to this, two differential pressure transmitters with 1 Pascal least count and range of − 50 Pascal to + 50 Pascal are mounted to the right side wall of the furnace to maintain the pressure condition during the test.

4.2 Jet Fire (ISO 22899-1)

To study the thermal performance of organic and inorganic coating material in jet fire exposure a test facility is developed as per ISO 22899-1 [12] and ISO 22899-2 [33]. This test setup aims to simulate the thermal and erosive loads imparting on the passive fire protection systems resulting from the high-pressure release of flammable jet flame i.e., liquefied petroleum gas (LPG), natural gas, etc. In comparison with the standard and hydrocarbon fire curves the jet fire imparts high heat fluxes on the product in the form of convective, and radiative heat fluxes as well as high erosive forces. To produce this level of heat fluxes, a 0.3 kg/sec sonic release of gas with 2.3 bar pressure was aimed at the steel specimen with coating. This jet was aimed directly at the center from distance of 1 m apart on the open-fronted re-circulation chamber to produce a fireball. A standard nozzle manufactured with stainless steel (SS 316L) [34] is used to release the natural gas with pressure.

The open-fronted box consists of a flame recirculation chamber and a protective chamber made with a mild steel plate of 10 mm thickness. The size of the re-circulation chamber is 1500 mm × 1500 mm × 500 mm and the protection chamber is of size 1500 mm × 1500 mm × 100 mm The entire set-up is constructed according to ISO 22899-1 [12]. The 3D model and the actual test setup at the site are shown in Figure 4a, b, respectively.

Figure 4
figure 4

(a) 3-dimensional model of Jet Fire test (ISO 22899-1 [12]) (b) Actual photograph of Jet Fire test (ISO 22899-1 [12]).

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During the test of jet fire, two different coating materials were applied on steel specimens in layers with a total thickness of 22 mm. The detailed procedure for the preparation of the steel specimen and chamber is given in Sect. 3.2. During the fire exposure, at a distance of 250 mm from the face of the specimen, the temperature inside the recirculation chamber was measured on the left and right sides of the web at different locations. A total of 6 K-type thermocouples namely R1, R2, and R3 on the right side and L1, L2, and L3 on the left side of the web inside the recirculation chamber are fixed at a height of 375 mm, 750 mm, and 1125 mm respectively from the base of the chamber. The 6 mm diameter k-type thermocouples R1, R2, and R3 were inserted through the plate on the right side of the chamber at a distance of 375 mm, 700 mm, and 375 mm respectively, 8 mm stainless steel tube encasing used to protect against the continuous thrust of jet fire. Similarly, L1, L2, and L3 were inserted from the left side plate of the chamber but at distinct locations of 100 mm, 200 mm, and 300 mm, respectively. These locations for thermocouples were kept the same as illustrated in Fig. 5 during both tests for organic and inorganic coating.

Figure 5
figure 5

Thermocouple location on re-circulation chamber for organic & inorganic material coating.

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In the case of the inorganic coating jet fire test, a total of 9 k-type thermocouples were fixed on the rear wall of the steel specimen (unexposed side of the specimen) as per the procedure given in the Annexure of ISO 22899-1 [12] to measure the temperature values on unexposed face of the specimen. The series of thermocouples is generally divided into four parts for easier and better analysis. The thermocouples on the right side were indicated by nomenclature as RK7, RK9, and RK1, and on the left side of the specimen they were LK3, LK4, and LK15. The thermocouples fixed on the centerline were numbered CK2, CK8, and CK14, and a group of five thermocouples WK6, WK10, WK12, WK13, and WK16 were inserted into the central web from the rear side of the specimen. The detailed procedure for inserting these thermocouples is given in Sect. 3.2 and the schematic diagram for the thermocouple location is shown in Figure 5. Out of all thermocouples, only CK2 malfunctioned during the test duration. However, in the case of organic coating similar procedures were followed but the nomenclature for thermocouples was different. On the right side, RK3, RK1, and RK5 were connected out of which RK5 malfunctioned. On the other hand, LK9, LK11, and LK7 were connected from which LK7 showed false readings during testing. CK4, CK14, and CK8 were connected at the centerline of the steel plate, and five central web thermocouples were inserted with identical nomenclatures for inorganic coating. Figure 5 clearly illustrates the location of these thermocouples.

5 Experimental Work

5.1 Fire Curves

In this work, experiments were conducted to examine how passive fire protection materials behave under various types of fire exposure conditions. The thermal performance and efficacy of two end products, one organic and the other inorganic, used to protect steel are studied by subjecting them to various time–temperature exposure conditions. Experiments using three distinct time vs temperature curves, namely standard fire (ISO 834 [8]), hydrocarbon fire (UL 1709 [31]), and jet fire (ISO 22899-1 [12]) were conducted and the impact of heating conditions on the fire performance of passive fire prevention was studied.

5.2 Thermal Analysis

Thermogravimetric Analysis (TGA) and Differential Thermogravimetric Analysis (DTGA) were used to examine the thermal behavior of both organic and inorganic passive fire prevention materials [35]. Thermogravimetric analysis (TGA) is a type of thermal analysis in which the mass of a sample is measured over time as the temperature varies. This measurement reveals physical events such as phase transitions, absorption, adsorption, and desorption [35] and DTGA describes at which rate the mass is losing with increase in temperature. The thermal analysis was carried out using the universal TGA instrument. TGA and DTGA were performed using a 20 °C /min ramp technique in a nitrogen atmosphere. The detailed procedure as per ASTM E 1131 [36] was followed. The results of TGA and DTGA for both organic and inorganic materials are depicted in Figure 6, respectively.

Figure 6
figure 6

Thermogravimetric analysis results for organic and inorganic material.

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Organic compounds lost just 3% of their weight up to a temperature exposure of 165°C. After that, there was a 2.3% weight loss from 165°C to 240°C and a 5.3% weight loss from 240°C to 340°C. Weight loss was quick at 71% above a temperature of 340°C and up to 550°C. Our findings reveal that as a protective material throughout the early heating phase, i.e., up to 165°C, it performs admirably. The fast weight loss predicted by the coating's disintegration and decreasing thickness forecasts rapid heat transmission through the protective layer at temperatures over 340°C. For better performance the only exception is puffing; puffing enhances the layer of protection, and the puffed char protects the substrate. In contrast, the weight loss of inorganic material up to a temperature of around 100°C is insignificant. After that, or from 100°C to 240°C, there is a 14% weight loss. Additionally, between 240°C and 340°C, there is an average of 3.0% weight loss. Beyond that, it was around 3.5% between 340°C and 550°C, and 1.5% between 550°C and 860°C.

An interpretation in terms of the fire protection performance of this inorganic coating is done as the initial weight loss due to free and bound moisture water content. This amount of water content act as a shield and prevent the transmission of heat to a large extent, and depending on the thickness, it can give good fire protection to the substrate.

6 Results and Discussions

6.1 Fire Exposure Conditions

The fire exposure of specimens protected with passive fire protection materials i.e., organic and inorganic for standard and hydrocarbon tests was carried out with a vertical fire-resistant test furnace. The furnace temperature variation with time during the fire exposure was recorded at 16 different locations in the furnace. The average of all temperature values for all thermocouples is compiled and plotted in Figure 7. It is observed that, the temperature was well within the permissible limits as specified in standards of UL 1709 [11] and BS 476-20 [29] for hydrocarbon and standard fire exposure conditions respectively.

Figure 7
figure 7

Time–Temperature curve for standard fire (ISO 834 [8]) and Hydrocarbon fire (UL1709 [11]).

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In the case of jet fire tests temperatures were measured on the exposed side i.e., inside the re-circulation chamber at six different locations. Three thermocouples were on the right side (R1, R2 and R3) and three on left (L1, L2 and L3) in front of nozzle as illustrated in Figure 5a for organic and inorganic coating, respectively. The detailed temperature profiles of the exposed side of the jet fire test with inorganic coating are shown in Figure 8a. In addition to this, the average of the temperatures on the left and right side of the re-circulation chamber are plotted in Figure 8b. Similarly, the temperature variation recorded in the re-circulation chamber plotted for organic material is depicted in Figure 9a, and the average temperature profile is in Figure 9b. The duration of jet fire exposure for inorganic coating was recorded at 90 min and for organic coating it was recorded at 27 min.

Figure 8
figure 8

(a) Temperature profile of the flame re-circulation chamber for inorganic coating (b) Average temperature profile for the right and left side of the re-circulation chamber for inorganic Coating.

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Figure 9
figure 9

(a) Temperature profile of flame re-circulation chamber for organic coating. (b) Average temperature profile for the right and left side of the re-circulation chamber for organic coating.

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Since, the jet fire test was carried out in an outside environment, a temperature variation was observed on the left and right sides of the web due to wind effects and air velocity, even with the use of windshields.

6.2 Visual Observation

In each case, visual observations were taken after the fire exposure as per standard, hydrocarbon, and jet fire heading conditions to analyse the impact of the fire exposure on the behaviour of organic and inorganic fire protective material, with respect to the bonding with the steel surface, cracking, and material’s strength degradation.

6.2.1 Standard Fire Exposure (ISO 834)

Specimens protected with inorganic and organic passive fire protection material were exposed to the standard heating condition. Before taking the specimen out of the furnace, the actual condition of the specimen was photographed as shown in Figure 10a, b. As depicted in Figure 10a, the remains of inorganic material showed little swelling and the formation of a hard crust. The material was found intact and adhered to the steel surface without any crack. Whereas, in the case of organic fire protection material Figure 10b, the fire exposure resulted in the foaming of material and the formation of black char. De-bonding of coating with the surface of steel was observed but almost the entire I section was covered with protective material.

Figure 10
figure 10

(a) Condition of inorganic protective coating before and after exposure to standard, a hydrocarbon fire condition. (b) Condition of organic protective coating before and after exposure to standard, a hydrocarbon fire condition. (c) Condition of inorganic protective coating before and after exposure to a jet fire condition. (d) Condition of organic protective coating before and after exposure to a jet fire condition.

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6.2.2 Hydrocarbon Fire Exposure (UL 1709)

In the case of inorganic PFP material, a portion of material flowed down vertically leaving with thin protection layer on the upper half portion of the steel I section as shown in Figure 10a. Furthermore, on the lower half portion of the protected I section, an increase in the thickness of.the material was observed. This was due to the accumulation of material that flowed downward and hardened during cooling. The organic coating showed puffing and de-bonding with the steel surface after hydrocarbon fire exposure similar to standard fire exposure conditions as shown in Figure 10b. However, as compared to standard heating conditions, at some places coating was not present and the bare steel surface was visible after hydrocarbon fire exposure.

6.2.3 Jet Fire Exposure (ISO 22899-1)

It was found that for organic passive fire protection material, the material begins puffing and blowing out in the environment from the surface of the steel with the turbulence of jet fire during the early stages of jet fire exposure. At the end of the test, i.e., 27 min, it was observed that the effective thickness of the protection material on the steel surface was negligible as shown in Figure 10d. The inorganic coating, on the other hand, begins to swell when exposed to jet fire. Subsequently, it begins to collapse in layers exposing the next layer of protective material. After 90 min of jet fire exposure, the protection material was present on the steel surface, and in a few locations bare steel surface was visible. This may be due to the erosive action of the jet on the tested specimen as shown in Figure 10c.

6.3 Fire Performance of the Protective Coating

The fire performance of protective materials of 22 mm thickness was analyzed with the help of variation in temperature recorded on the surface of protected steel specimen after exposure to the three different types of fire conditions of standard heating, hydrocarbon heating, and jet fire. Visual observations were taken after fire exposure and subsequent cooling. All the compiled results are shown in Figure 11.

Figure 11
figure 11

Thermal performance of steel specimen coated with passive fire protection material in standard, hydrocarbon, and jet fire conditions.

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The relative fire performance of PFP materials in various types of fires is discussed based on the temperature limit of 648 0C which is specified in ASTM E119 [9] as the critical temperature that should not rise on any point of protected steel surface. It is observed that in the case of standard heating conditions for organic PFP material, it took 115 min to reach the critical temperature, while for hydrocarbon and jet fire conditions it took 68 min and 9 min respectively, as depicted in Figure 11. The time taken to attain the maximum temperature of 648 0C was less in hydrocarbon time–temperature fire exposure (UL1709 [11]) as compared to standard heating conditions (BS 476 [29]). The difference in time was 47 min. This variation in performance is caused by a change in the behavior of protection material with respect to the fast rate of heating, and higher elevated temperature in hydrocarbon fire exposure in comparison with standard fire exposure. Figures 12a–d depicts the temperature fluctuation recorded on the protected steel surface at various places during jet fire exposure for organic PFP protection material with a protection thickness of 22 mm. It is observed that the temperature on the unexposed face of the steel surface was higher on the right-hand side thermocouples (RK3 and RK1) as compared to the left side (LK9 and LK11) and centerline thermocouples (CK4 and CK14). It is justified since the exposed face temperature on the right-hand side were higher owing to flame deflection due to wind direction. Furthermore, the web temperatures (WK6, WK7, WK12, WK13, and WK16) were the highest. This is because these thermocouples are exposed from all sides and surrounded by protection material. Figure 12e depicts a comparison of the average temperature on the right side (RK3 and RK1), left side (LK9 and LK11) center line (CK4, CK14), and web (WK6, WK7, WK12, WK13, and WK16). Temperature variation observed on the web at different locations showed almost identical behavior. In 9 min, the maximum temperature limit of 648°C at any point was attained. However, for the same thickness of protection for standard and hydrocarbon fire, it was 115 min and 68 min, respectively. In the event of a hydrocarbon fire, the exposed side temperature of about 1095°C was obtained in about 10 min and was maintained throughout fire exposure. In the instance of a jet fire, a temperature of around 1200°C was attained in less than 5 min and maintained for the duration of fire exposure. The little change in the intensity of fire exposure between jet fire and hydrocarbon fire, a significant difference in the fire performance of the organic type of passive fire protection material is accomplished. This is due to the tremendous impact of jet fire and associated turbulence as well as the erodable effect. In this situation, the organic PFP material intumesces at high temperature and the char generated is not strong enough to bear the jet fire turbulence. Therefore, when the protected surface was exposed to jet fire, the intumescent organic PFP material transformed into char and flew away due to the strong impact of jet fire, leaving the steel surface exposed to fire.

Figure 12
figure 12figure 12

Temperature variation profile for the unexposed side of the specimen with organic material (a) Right Side of specimen (b) left side of specimen (c) web thermocouples (center line) (d) center line on specimen (e) Average temperature of all thermocouple.

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As a result, adequate analysis of the predicted fire scenario to which PFP material might be exposed over its functional life is essential. Therefore, before selecting and installing these materials, the fire resistance rating should be evaluated under site representative conditions. A similar series of experiments were also carried out for inorganic coating. Figure 11 depicts temperature fluctuation on the protected steel surface with a 22 mm thickness of inorganic passive fire protection material when exposed to standard, hydrocarbon, and jet fire conditions. In the case of inorganic material, it took 138 and 87 min to reach a critical temperature of 648°C, on the surface of protected steel when exposed to standard fire and hydrocarbon fire conditions respectively.

As subjected to standard heating conditions, it took 48 min longer to achieve critical temperature of 6480C on the surface of protected steel when compared to hydrocarbon heating conditions. In case of jet fire exposure, the temperature variation at different locations on the left side (LK2, LK4, and LK15), right side (RK7, RK9, and RK11), the centre line of the plate (CK8, Ck9) and web (WK6, WK10, WK12 and WK13, WK16) were recorded and plotted in Figure 13a–d. Temperatures on the left side (LK2, LK4, and LK15) were found to be lower than those on the right-hand side (RK7, RK9, and RK11) and middle line of the plate (CK8, Ck9) thermocouples. It was caused by the wind effect and the flame tilted to the right side of the recirculation chamber. The temperature measured by the thermocouple put in the web (WK6, WK10, WK12, and WK13and WK16) was higher than all other thermocouples on the unexposed side. The highest temperature recorded on the web was caused by material spalling, leaving a bare steel surface exposed to fire and direct thrust of jet fire impingement. In the case of jet fire exposure, the critical temperature of 648 0C was reached after 67 min. The added impact of turbulence, jet thrust, and erosion influenced the final performance. In all three cases of fire exposure, the behaviour of protection material was the same throughout the first 28 min of exposure. However, it was the same for both standard fire and hydrocarbon fire up to roughly 40 min.

Figure 13
figure 13figure 13

Temperature variation profile for the unexposed side of the specimen with inorganic material (a) Right Side of specimen (b) left side of specimen c web thermocouples (center line) (d) center line on specimen (e) Average temperature of all thermocouple

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In all three tested fire scenarios, the surface temperature of steel was less than 100°C for up to 28 min of fire exposure. When the inorganic coating is exposed to high temperatures, it begins to swell and forms an exterior surface hard crust. In all three cases, the damage to the coating was limited only to the upper layer during the first 28-min fire exposure. However, after 40 min of exposure to hydrogen fire, the protection layer sustained more damage. The surface temperature of protected steel increased more in hydrocarbon fire exposure than in standard fire exposure. The reason is due to the intensity of the fire and the corresponding thermal behaviour of inorganic passive fire protection material. In jet fire exposure, localized damage in the protective layer occurred after 28 min owing to the jet fire turbulence, resulting in a faster rate of temperature rises on the protected steel surface compared to hydrocarbon and standard fire exposure. Nevertheless, the maximum temperature, 648°C, was obtained simultaneously in both hydrocarbon and jet fire exposures. However, the inorganic passive fire protection material behaved differently in all three fire scenarios while having the same thickness of the coating.

It is worth highlighting the relative performance of an organic and inorganic coating in the jet fire exposure condition, with the expectation that the PFP materials, in which intumescent and soft char was formed, are extremely vulnerable in the jet fires exposure conditions, in contrast to other materials that don’t lose strength at elevated temperature of that order. Additionally, this study can extend to look more into the protection of concrete surfaces with a coating of organic and inorganic material, because in fire concrete degrades its material property [36, 37]. With the help of developed material, it can be protected in applications like blast walls on oil and gas platforms.

7 Conclusion

The findings derived from the experiment results and the examination of material behavior are given below:

  • Thermal analysis revealed that at lower temperatures of less than 350 0C, organic protection material outperforms inorganic protection material with a total weight loss of 12.75% compared to 20%. At temperatures over 350°C, organic coatings reduce significantly in weight compared to inorganic ones. The organic coating had 18.4% residual weight at 550 0C, whereas the inorganic coating had 79.5%.

  • Based on experimental studies, it can be inferred that a combination of inorganic and organic protective material, with inorganic material directly confronting the fire and organic on the inner side, would provide superior fire performance.

  • All samples protected with the organic and inorganic PFP material and subjected to various fire exposure conditions, such as standard fire, hydrocarbon fire, and jet fire, exhibited varied temperature rises on the protected steel surface, according to the experimental findings. The temperature increase on the surface of protected steel in each case was minimal in standard fire exposure and maximal in jet fire exposure.

  • The fundamental explanation for this is found in the variations in the rate of heating and maximum temperature obtained in various fire exposure situations, which caused the varied physical condition of the organic and inorganic PFP material as seen by visual inspection after fire exposure in each instance.

  • Before determining the application of any fire protection material, particularly in key installations, its fire performance must be evaluated in a large-scale test imitating a more realistic fire situation.