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Article

Experimental Study on the Melt Dripping Behavior of Flexible Polyurethane Foam in an Oscillating Ship Cabin

by
Wenfeng Shen
1,2,3,
Zhenyu Wang
1,3,
Dimeng Lai
1,2,3,
Yujin Huang
1,
Huanghuang Zhuang
1,3,
Zhongqin Liu
1,2 and
Hongzhou He
1,2,3,4,*
1
Key Laboratory of Clean Energy Utilization and Development in Fujian Province, Jimei University, Xiamen 361021, China
2
Fujian Province Clean Combustion and Energy Efficient Utilization Engineering Technology Research Center, Jimei University, Xiamen 361021, China
3
College of Marine Equipment and Mechanical Engineering, Jimei University, Xiamen 361021, China
4
Zhangzhou Institute of Technology, Zhangzhou 363000, China
*
Author to whom correspondence should be addressed.
Fire 2025, 8(11), 446; https://doi.org/10.3390/fire8110446 (registering DOI)
Submission received: 15 September 2025 / Revised: 31 October 2025 / Accepted: 12 November 2025 / Published: 17 November 2025
Browse Figures
Versions Notes

Abstract

Flexible polyurethane foam (FPUF) is widely used in ship cabins yet poses significant fire hazards due to its flammability and tendency to melt and drip during combustion. While previous studies have primarily focused on dripping behavior under static conditions, the effect of oscillatory motion, typical in maritime environments, remains poorly understood. This study investigated the dripping behavior of FPUF under both static and oscillating conditions using a custom-made experimental platform simulating ship motions. The results reveal that under static conditions, side ignition leads to a higher dripping frequency than central ignition. Under oscillation, central ignition produces a greater number of drips and higher dripping frequency compared to static conditions. Although oscillation promotes the formation of smaller droplets and reduces the proportion of large-size flaming drips, the absolute number of such flaming drips increases, elevating fire spread risk. Furthermore, while oscillation frequency and amplitude have limited effects on dripping frequency, they significantly expand the dripping spread range, which increased by over 300% at 30° and 0.1 Hz compared to static conditions. These findings provide insights for improving fire risk assessment and safety design of polymeric materials in dynamic operational environments such as ships.

1. Introduction

Flexible polyurethane foam (FPUF) and other polymer materials are widely used in ship cabins as furniture fillers and for other purposes. However, these materials are highly flammable and pose considerable fire risks. In particular, thermoplastic and thermosetting materials will undergo melting, flowing, and dripping during combustion [1,2,3,4]. Existing studies have shown that dripping may remove combustibles and heat, thereby retarding the combustion of the material itself or even leading to self extinguishment [5,6]. However, it is more common that molten drips carrying flames fall and ignite pool fires or act as “secondary ignition sources” for the underlying combustibles, expanding the fire spread [7,8,9,10]. Moreover, melt flow and dripping can alter the flame propagation path and form new fire spread patterns. Therefore, studying dripping behavior is essential for understanding the polymer combustion mechanism, improving flame retardancy, and optimizing the fire dynamic models.
The melting and dripping behavior of thermoplastic polymers has been relatively systematically studied, covering the formation mechanism of molten drips, influencing factors and their effects on fire dynamics. Kandola et al. [11] noted that dripping results from the combined action of physical melting, chemical decomposition, and pyrolysis reduces the viscosity of the melt [12]. Zhang et al. [13] reported that the extent of melting is closely related to the glass transition temperature and melting point of the material. The lower the glass transition temperature or melting point, the more significant the melting. Wang et al. [5,14,15] systematically studied the dripping behavior of vertically oriented strip samples under burning or heating conditions using a modified UL-94 setup. They found that dripping frequency is negatively correlated with the droplet size and closely associated with the material’s decomposition mechanism. When random-chain scission dominates, the molecular weight decreases rapidly, leading to small droplets and high dripping frequency. When decomposition is dominated by depolymerization, cross-linking or cyclization, the molecular weight decreases slowly or even increases, resulting in large droplets and a long dripping time. Melt viscosity is a key factor affecting dripping. Bulter [16], combining experimental measurements and the particle finite element method (PFEM) [17] simulations, found that pyrolysis of thermoplastic material’s melts can effectively reduce viscosity and promote flow. Xie et al. [8,18,19] indicated that the melt dripping rate is inversely proportional to the melt viscosity. Some flame retardants (such as phosphorus-based flame retardants) reduce or suppress dripping by increasing melt viscosity [4,20]. In addition to the material pyrolysis mechanism and melt rheological properties, other factors influencing the dripping behavior of thermoplastic materials include ambient oxygen concentration [6,21,22], pressure [21,22,23,24], and heat transfer conditions [25,26]. Dripping will also change the fire spread mode. Xie et al. [8,18,19] observed that dripping droplets of polypropylene (PP) and polyethylene (PE) undergo intense burning during the falling process, accelerating the spread of pool fire. Luo et al. [9,27] studied downward burning of extruded polystyrene (XPS) foam and found that flame spread accelerated abruptly once the accumulated melt dripped. Huang et al. [28] first proposed the concept of critical drip size, suggesting that droplets with a diameter of D0 > 0.7 mm can carry flame to the ground. Sun et al. [29] further proposed that the ignition of paper by flaming droplets is mainly influenced by droplet mass and dripping frequency.
In contrast, research on the dripping behavior of thermosetting materials, such as FPUF, started later, and its mechanism is more complex. The melt from FPUF is not melted polymer itself but rather its pyrolysis product [30,31], and the relevant pyrolysis mechanism has been relatively well studied [32,33,34]. Pau et al. [35] investigated the combustion, melting, and dripping behavior of FPUF under vertical fire exposure, and found that the dripping behavior mainly depends on the density and char-forming property of the material. The high-density, char-forming foam has higher dripping frequency, higher melt viscosity, and a greater proportion of drips, while the low-density, non-char-forming foam tends to gasify more with a lower proportion of drips. Using a top-center ignition setup, Liu et al. [36] and McKeen et al. [31] observed that the FPUF melt primarily forms in the center area of the material’s upper surface. As combustion proceeds, the melt flows to the boundary and drips vertically due to foam contraction, potentially igniting pool fire. Chen et al. [30,37] further studied the vertical dripping behavior of the melt from the boundary of FPUF and found that it is significantly affected by the drip size, dripping height, and ambient humidity. Droplets smaller than 0.7 mm typically burn out in the air, while those larger than the critical drip diameter may carry flames and pose a risk of igniting underlying combustibles. In addition, critical drip diameter increases linearly with the dripping height. In a high-humidity marine environment, increased humidity significantly reduces the number of drips and the probability of flame carrying. Jiang et al. [38] constructed a green halogen-free coating and effectively suppressed the dripping of FPUF during combustion through a synergistic mechanism of promoting char formation and building a barrier.
The above studies provide a crucial foundation for understanding the dripping behavior of FPUF and clarify the influence of environmental factors (e.g., humidity) and material properties (e.g., density, flame retardant addition) on dripping. However, most studies focus on the combustion behavior under static conditions. In practical applications such as ships and rail transit, polymer materials are often subjected to dynamic mechanical environments like oscillation and vibration [39]. Oscillation not only changes the stress state of melt, but also may affect its flow path, thus affecting key parameters such as droplet mass and dripping frequency. At present, the effect of dynamic conditions on the combustion and dripping behavior of thermosetting materials such as FPUF is not clear, and there is a significant gap in relevant research.
Therefore, this study focuses on the dripping behavior of burning melt of FPUF under oscillation conditions. The effects of oscillation parameters (such as oscillation frequency and amplitude) on the combustion characteristics and melt dripping behavior of FPUF are investigated by constructing an oscillating experiment setup, providing theoretical support for fire risk assessment and material safety design in dynamic scenarios such as ships.

2. Materials and Methods

2.1. Materials

The FPUF used in this study was manufactured by Hangmei Sponge Co. (Hangzhou, China), with a density of 23.5 kg/m3 and an average heat value of approximately 24 kJ/g. Elemental analysis of the FPUF, conducted using a PerkinElmer 2400 analyzer (Elementar Analysensysteme GmbH, Langenselbold, Germany), is summarized in Table 1. The ignition characteristics of the FPUF were measured using a cone calorimeter. As shown in Figure 1, the ignition time decreased significantly as the external heat flux increased from 20 to 50 kW/m2, which confirmed the high flammability of the FPUF. To further explore how fuel size affects melt dripping behavior, four different sample dimensions were selected: ① 100 × 100 × 50 mm; ② 100 × 100 × 25 mm; ③ 200 × 200 × 50 mm; and ④ 200 × 200 × 25 mm (length × width × height).

2.2. Experimental Setup and Procedure

The experiments were performed on a custom-made apparatus capable of investigating the burning and melt dripping of FPUF under oscillating conditions, as illustrated in Figure 2. The system mainly consists of a combustion platform, an upper platform, a lower platform, and a drive mechanism. The FPUF sample is placed at the center of the combustion platform, with droplets collected on the upper platform. The droplet spread range is determined by measuring the maximum distance between the landing positions of any two droplets. The upper and lower platforms are supported by a transmission module, support rods, and a retractable guidance mechanism. By adjusting the motor speed and stroke, the oscillation frequency of the upper platform can be controlled within the range of 0.01–0.2 Hz, with an oscillating amplitude of up to ±35°. The distance between the combustion platform and the upper platform is 50 cm. An external frame is used to mount an exhaust hood directly above the combustion platform, allowing for the removal of smoke generated during combustion. The lower platform serves to hold counterweights and maintain the stability of the experimental apparatus during testing. To facilitate the observation of combustion and melt dripping behavior, the experiments were recorded using a Canon EOS-M50 camera (24.1 million pixels, 60 fps max video frame rate). The camera distance from the setup was adjusted as needed for optimal observation.
Prior to each test, the platform was leveled, and control parameters were set according to the target amplitude and frequency. The exhaust fan was activated, and the sample was placed at the center of the wire-mesh combustion platform with its four corners fixed using iron wires. Ignition was achieved using a flame igniter, simultaneously with the activation of the oscillation mechanism. As shown in Figure 3a, center ignition was performed at the center of the FPUF sample’s upper surface, while side ignition was performed at the midpoint along one edge of the FPUF sample. During oscillation, the combustion platform and the upper platform tilt around the central support rod, with the motion illustrated in Figure 3b.
The experiments adopted the controlled-variable method, and all FPUF samples were consistent in specification. For comparing dripping behavior under static and oscillating conditions, the amplitude was set to ±25° with a period of 10 s. To examine the effect of oscillation frequency, central ignition was applied with a fixed amplitude of ±30° and a dripping height of 50 cm. The selected frequencies were 0.125 Hz, 0.1 Hz, 0.083 Hz, 0.0714 Hz, and 0.0625 Hz, corresponding to periods of 8 s to 16 s. For studying the influence of oscillation amplitudes, the frequency was fixed at 0.1 Hz with a dripping height of 50 cm, and the amplitudes were set to 15°, 20°, 25°, and 30°. These parameter ranges were chosen based on typical ship motion conditions [39]. Each test condition was repeated at least three times, and the standard deviation of the measured data was calculated, providing a quantitative assessment of the experimental scatter.

3. Results

3.1. Effects of Sample Size and Ignition Location on Dripping Behavior Under Static Conditions

Chen et al. [30,37] investigated the combustion and dripping behavior of 50 mm thick FPUF under central ignition in static conditions. This study expands on their work by examining the effects of sample size and ignition location. Figure 4 illustrates the combustion behavior of samples with different thicknesses under central ignition in a static state. For thicker samples ① and ③ (50 mm), the flame initially spreads rapidly across the upper surface, then propagates laterally, and eventually reaches the bottom. During combustion, a char-like molten residue forms on the surface within the burning zone, leading to structural collapse. The molten material gradually coalesces into droplets that drip from the edges. The porous structure of FPUF softens and contracts upon heating, and the rupture of pore walls leads to overall structural collapse, which promotes the formation and flow of molten material [30,31,32,33,36]. In contrast, thinner samples ② and ④ (25 mm) collapse more readily and undergo rapid burning due to their reduced thickness. As shown in Figure 4b, for larger surface area samples such as ④, a ring-like structure forms in the later stages of combustion due to central collapse and complete consumption, with dripping occurring both at the edges and the center. Under side-ignition conditions, the combustion process of FPUF begins with flame propagation across the upper surface of the FPUF sample. After a period of time, the foam structure at the ignition site becomes compromised, forming an outward-sloping collapse surface from which molten material starts to drip. As combustion continues, the flame further spreads to cover the entire sample. As shown in Figure 5, this stage is characterized by increased molten material generation, resulting in noticeably larger droplet sizes. The intense combustion process persists until the FPUF is completely consumed. As shown in Figure 5b, for thinner FPUF samples, the material near the ignition side burns out more completely.
Table 2 presents melt dripping data of four FPUF sample sizes under both center- and side-ignition conditions, where the average dripping frequency = average number of drips/average burning time. As indicated in Table 2, the size of the FPUF sample influences the average dripping frequency of molten material. For both center and side ignition, larger samples correspond to higher average dripping frequencies. A larger sample size entails a greater fuel load, which prolongs the burning time and significantly increases the total amount of molten material and the number of drips.
Furthermore, Table 2 shows that the ignition location significantly affects the dripping behavior of FPUF. The average dripping frequency under side ignition is considerably higher than under center ignition. In terms of the dripping process, center ignition leads to symmetric flame spread, and collapse occurs primarily at the center. Pyrolyzed polyol forms small bead-like droplets at the central upper surface, which then flow laterally, coalesce, grow in size, and eventually drip from the bottom [30]. Under side ignition, both flame spread and structural collapse exhibit noticeable asymmetry. An outward-sloping collapse surface forms earlier on the ignition side, along which molten material slides under gravity. As the flame propagates, unburned material continues to supplement the fuel near the flame, resulting in a more continuous generation and dripping of molten material and consequently a higher number of drips compared to center ignition.
Although the flame spread rate under center ignition is faster than under side ignition [40], the increased number of drips under side ignition leads to more rapid mass loss. Thus, for the same sample size, the total burning time remains similar under both ignition modes. However, due to the higher number of drips, the dripping frequency under side ignition is significantly greater.

3.2. Dripping Behavior Under Static and Oscillating Conditions with Different Ignition Locations

Figure 6 and Figure 7 show the combustion and melt dripping behavior of a 50 mm thick FPUF under central ignition in static and oscillating conditions, respectively. The flame morphology differs between the two states, and the flame is relatively symmetric under static conditions, which may alter the distribution of pyrolysis products on the sample surface. In static condition, molten material drips vertically, landing within an area roughly corresponding to the surface of the FPUF sample. Under oscillation, molten droplets follow parabolic trajectories, indicating that they acquire horizontal initial velocity prior to dripping. This results in a significantly larger dripping spread range, increasing by over 500% at an amplitude of 30° and a frequency of 0.1 Hz.
Table 3 compares the melt dripping behavior of a 50 mm thick FPUF under static and oscillating conditions for different ignition locations. Under central ignition, the burning time is similar in static and oscillating conditions, but the number of drips and the dripping frequency are higher under oscillation. Dripping begins in the middle phase of the total burning time and occurs more rapidly under oscillation. The oscillatory motion imposes periodic inertial forces on the molten material, accelerating its coalescence and separation, thereby increasing the dripping frequency. The increase in dripping frequency under side ignition is less pronounced than under central ignition, which can be attributed to differences in the mechanisms of melt formation and accumulation between the two ignition modes. As described in Section 3.1, under static conditions, side ignition already facilitates efficient dripping via an outward-sloping collapse surface along which molten material flows under gravity. Although inertial forces from oscillation can further promote dripping, the marginal benefit is reduced. Additionally, the limited size of the FPUF samples used in this study may restrict the total amount of molten material formed after ignition, leading to a smaller increase.
Figure 8 and Figure 9 show the dripping patterns of different-sized droplets under central ignition in static conditions. Small-size drips, referred to as “fire-free drips,” extinguish before landing on the lower platform. Large-size drips, termed “flaming drips,” remain flaming upon impact and pose a risk of igniting underlying combustibles, potentially leading to fire spread. Under central ignition, the proportion of flaming drips under oscillation is about 43%, lower than that under static conditions (approximately 50%). This suggests that shear forces induced by oscillation promote the breakup of molten material into smaller droplets. However, due to the higher total number of drips under oscillation, the absolute number of flaming drips is greater, indicating a higher risk of fire spread under oscillation and highlighting the dual effect of oscillatory motion on the dripping behavior.

3.3. Effects of Oscillation Frequency and Amplitude on Dripping Behavior

Table 4 summarizes the dripping behavior at different oscillation frequencies. The number of drips and the dripping frequency show no significant variation across frequencies, indicating that oscillation frequency has minimal influence on the dripping frequency of molten material during FPUF combustion. However, as shown in Figure 10, the dripping spread range expands with increasing oscillation frequency. At a dripping height of 50 cm, the dripping range increases from 71 cm to 79 cm as the oscillation period shortens from 16 s to 8 s. When the amplitude is constant, higher oscillation frequencies increase the angular velocity, imparting greater initial velocity to the drips and propelling them further, thereby enlarging the dripping spread range and increasing fire spread risk. Moreover, as indicated in Table 4, lower oscillation frequencies favor the formation of larger droplets, consistent with the findings in Section 3.2.
Table 5 summarizes the dripping behavior at different oscillation amplitudes. The average number of drips and the average dripping frequency are not significantly affected by amplitude. However, as shown in Figure 11, under central ignition, the dripping spread range of molten materials increases linearly with amplitude. When the frequency is constant, a greater amplitude raises the angular velocity and the tangential velocity at which droplets are ejected, resulting in a wider dripping spread range.
Although oscillation generally increases the dripping frequency of FPUF combustion droplets, the specific frequency and amplitude have a limited influence. A potential explanation is that the system reaches a relative dynamic equilibrium during oscillation: as frequency or amplitude increases, dripping from the downward-inclined side is promoted, while dripping from the upward-inclined side is suppressed, thereby maintaining the total number of drips. This mechanism dampens the effect of oscillation parameters on the overall dripping frequency but significantly alters the spatial distribution characteristics of the drips, namely, expanding the dripping spread range.

4. Discussion

This study has experimentally revealed the influence of ship oscillation motions on the combustion dripping behavior of FPUF.
First, regarding dripping frequency and proportion of flaming drips, under center-ignition mode, oscillation significantly increased the dripping frequency from 0.117 Hz under static conditions to 0.401 Hz. The underlying mechanism is that the periodic oscillation of the platform imposes additional inertial forces on the molten material accumulated on the FPUF surface. This dynamic shear action promotes the coalescence and separation processes of molten droplets, thereby accelerating dripping. However, a seemingly contradictory yet crucial finding is that while oscillation increases the total dripping frequency, it reduces the proportion of large flaming droplets from 50% (static) to 43% (oscillation). This is likely because the shear forces induced by oscillation tend to break large molten masses into smaller droplets. According to the critical diameter theory established by Chen et al. [30,37], smaller droplets are more prone to extinguish during falling due to insufficient mass or cooling effects. Nevertheless, due to the increase in the total number of drips (from 17 to 61), the absolute number of flaming droplets actually increased from approximately 9 to 26. This quantitative relationship clearly reveals the dual effect of oscillation: on one hand, it reduces the ignition potential of individual droplets through fragmentation; on the other hand, it ultimately leads to a higher number of potential ignition sources by increasing the total number of drips, thereby significantly elevating the macroscopic risk of fire spread.
Second, regarding the dripping range, this study observed that under oscillatory conditions of 30° and 0.1 Hz frequency, the dripping spread range expanded by over 300% compared to static conditions. The extension of the dripping range primarily stems from two components: (1) displacement caused by the initial horizontal velocity imparted to droplets by platform oscillation; and (2) geometric displacement resulting from the maximum tilt angle of the platform itself. Ship oscillation not only simply alters dripping points through tilting but, more importantly, by imparting initial horizontal velocity to droplets, changes their motion trajectory from near-vertical falling under static conditions to parabolic paths. This effectively “throws” burning molten material to areas far from the fire source below, significantly increasing the probability of igniting surrounding combustible materials.
In summary, ship oscillation increases both the dripping frequency and the absolute number of flaming droplets through inertial shear mechanisms and substantially expands the dripping spread range through the combined action of imparting initial velocity and altering geometric angles. These two mechanisms work together to significantly enhance the fire risk induced by molten dripping during FPUF combustion in dynamic ship environments.
The literature reveals that the influence of environmental factors on melt dripping behavior of FPUF involves complex coupling relationships. Research by Chen et al. [37] indicates that high-humidity environments (RH ≥ 90%) can suppress the flaming probability of drips. In actual ship cabins, oscillation and high-humidity environments coexist. Future research should focus on the coupling effects of these two factors. Furthermore, there are certain differences between the oscillation mode in this study and actual ship motion, which more closely resembles simple harmonic motion.

5. Conclusions

This study provides the first systematic experimental investigation into the burning and dripping behavior of flexible polyurethane foam (FPUF) under dynamic oscillatory conditions that simulate a ship cabin environment using a custom-made experimental apparatus, moving beyond the traditional focus on static scenarios. The influence of oscillation frequency and amplitude on the dripping behavior of molten material was also analyzed. The main conclusions are as follows:
(1)
Under static conditions, noticeable differences were observed in the burning and dripping behavior of FPUF samples of different sizes. Under side ignition, the dripping frequency of FPUF samples of the same specification was significantly higher than under central ignition. Under central ignition, molten material from thicker samples (50 mm) dripped primarily from the edges, whereas thinner samples (25 mm) exhibited dripping from both the center and the edges.
(2)
Under central ignition, the total amount and frequency of molten dripping from FPUF samples of the same specification were markedly higher under oscillation than under static conditions. Oscillation-induced shear facilitates the breakup of molten material, leading to the formation of smaller droplets. The proportion of large-size flaming drips under oscillation was approximately 43%, lower than that under static conditions (50%). However, due to the increased total number of drips, the absolute number of large-size flaming drips was greater under oscillation, indicating a higher risk of fire spread.
(3)
Oscillation frequency and amplitude had minimal impact on the dripping frequency of molten material, but significantly influenced the dripping spread range. Under a constant dripping height of 50 cm, the dripping spread range expanded with increasing oscillation frequency or amplitude. At an oscillation amplitude of 30° and a frequency of 0.1 Hz, the dripping spread range increased by over 300% compared to the static condition, demonstrating that oscillatory motion greatly enhances the dispersal distance of molten material and the associated potential fire risk.

Author Contributions

Conceptualization, H.H.; methodology, Z.W. and Z.L.; validation, Z.W. and D.L.; formal analysis, Z.W.; investigation, Z.W. and Y.H.; resources, H.H.; data curation, Z.W. and H.Z.; writing—original draft preparation, Z.W. and W.S.; writing—review and editing, W.S. and H.H.; visualization, Z.W.; supervision, H.H.; project administration, H.H.; funding acquisition, H.H., W.S., and D.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Funding Project of Central Government Supporting the Development of Science and Technology of Fujian Province (Grant No. 2022L3013), the Natural Science Foundation of Fujian Province (Grant No. 2025J01873 and 2023J05159) and the Scientific Research Foundation of Jimei University (Grant No. ZQ2020013).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article or are available upon request.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Ignition time of FPUF as a function of external heat flux.
Figure 1. Ignition time of FPUF as a function of external heat flux.
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Figure 2. Schematic diagram of the custom-made apparatus capable of investigating FPUF melt dripping behavior under oscillating conditions.
Figure 2. Schematic diagram of the custom-made apparatus capable of investigating FPUF melt dripping behavior under oscillating conditions.
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Figure 3. Schematic diagram of ignition locations and apparatus oscillation.
Figure 3. Schematic diagram of ignition locations and apparatus oscillation.
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Figure 4. Combustion of (a) 50 mm thick and (b) 25 mm thick FPUF under central ignition in static state.
Figure 4. Combustion of (a) 50 mm thick and (b) 25 mm thick FPUF under central ignition in static state.
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Figure 5. Combustion of (a) 50 mm thick and (b) 25 mm thick FPUF under side ignition in static state.
Figure 5. Combustion of (a) 50 mm thick and (b) 25 mm thick FPUF under side ignition in static state.
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Figure 6. Flame morphology and melt dripping of the FPUF sample ③ under center ignition in static condition.
Figure 6. Flame morphology and melt dripping of the FPUF sample ③ under center ignition in static condition.
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Figure 7. Flame morphology and melt dripping of the FPUF sample ③ under central ignition in oscillating condition.
Figure 7. Flame morphology and melt dripping of the FPUF sample ③ under central ignition in oscillating condition.
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Figure 8. Small-size (fire-free) drips formed during FPUF combustion under center ignition in static state.
Figure 8. Small-size (fire-free) drips formed during FPUF combustion under center ignition in static state.
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Figure 9. Large-size (flaming) drips formed during FPUF combustion under center ignition in static state.
Figure 9. Large-size (flaming) drips formed during FPUF combustion under center ignition in static state.
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Figure 10. Melt dripping spread range of FPUF samples under oscillating conditions with different oscillating frequency.
Figure 10. Melt dripping spread range of FPUF samples under oscillating conditions with different oscillating frequency.
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Figure 11. Melt dripping spread range of FPUF sample under oscillating conditions with different oscillating amplitude.
Figure 11. Melt dripping spread range of FPUF sample under oscillating conditions with different oscillating amplitude.
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Table 1. Elemental composition of the selected FPUF.
Table 1. Elemental composition of the selected FPUF.
ElementsProportion (%)
C56.8 ± 0.17
H9.5 ± 0.03
O17.6 ± 0.08
N6.2 ± 0.13
S0.4 ± 0.17
other9.5 ± 0.03
Table 2. Melt dripping data of FPUF samples with different sizes under center- and side-ignition conditions.
Table 2. Melt dripping data of FPUF samples with different sizes under center- and side-ignition conditions.
Ignition
Position		SampleSize
(mm × mm × mm)		Average Burning Time
(s)		Average Drip Number
(Drops)		Average Drip Frequency
(Drops per Second)
Center①100 × 100 × 50145170.117
Center②100 × 100 × 259690.094
Center③200 × 200 × 50171350.205
Center④200 × 200 × 25128150.117
Side①100 × 100 × 501401060.757
Side②100 × 100 × 2588560.636
Side③200 × 200 × 501752371.354
Side④200 × 200 × 251221441.180
Table 3. Melt dripping data of FPUF samples under different ignition locations under static and oscillating conditions.
Table 3. Melt dripping data of FPUF samples under different ignition locations under static and oscillating conditions.
Ignition
Position		Platform
State		Average Burning Time
(s)		Average Drip Number
(Drops)		Average Drip Frequency
(Drops per Second)
CenterStatic145170.117
CenterOscillating152610.401
SideStatic1401060.757
SideOscillating1381531.109
Table 4. Melt dripping data of FPUF samples under oscillating conditions with different oscillating frequency.
Table 4. Melt dripping data of FPUF samples under oscillating conditions with different oscillating frequency.
Oscillating
Frequency
(Hz)		Average Burning Time
(s)		Average Drip Number
(Drops)		Average Drip
Frequency
(Drops per Second)		Proportion of Large-Size Drips
(%)
0.125146610.41842.6
0.1143600.41943.3
0.0833145590.40744.0
0.0714144630.43847.6
0.0625150580.38748.3
Table 5. Melt dripping data of FPUF samples under oscillating conditions with different oscillating amplitude.
Table 5. Melt dripping data of FPUF samples under oscillating conditions with different oscillating amplitude.
Oscillating
Amplitude		Average Burning Time
(s)		Average Drip Number
(Drops)		Average Drip Frequency
(Drops per Second)		Proportion of Large-Size Drips
(%)
15°128580.45344.8%
20°127600.47245.0%
25°124590.47644.0%
30°125610.48844.2%
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MDPI and ACS Style

Shen, W.; Wang, Z.; Lai, D.; Huang, Y.; Zhuang, H.; Liu, Z.; He, H. Experimental Study on the Melt Dripping Behavior of Flexible Polyurethane Foam in an Oscillating Ship Cabin. Fire 2025, 8, 446. https://doi.org/10.3390/fire8110446

AMA Style

Shen W, Wang Z, Lai D, Huang Y, Zhuang H, Liu Z, He H. Experimental Study on the Melt Dripping Behavior of Flexible Polyurethane Foam in an Oscillating Ship Cabin. Fire. 2025; 8(11):446. https://doi.org/10.3390/fire8110446

Chicago/Turabian Style

Shen, Wenfeng, Zhenyu Wang, Dimeng Lai, Yujin Huang, Huanghuang Zhuang, Zhongqin Liu, and Hongzhou He. 2025. "Experimental Study on the Melt Dripping Behavior of Flexible Polyurethane Foam in an Oscillating Ship Cabin" Fire 8, no. 11: 446. https://doi.org/10.3390/fire8110446

APA Style

Shen, W., Wang, Z., Lai, D., Huang, Y., Zhuang, H., Liu, Z., & He, H. (2025). Experimental Study on the Melt Dripping Behavior of Flexible Polyurethane Foam in an Oscillating Ship Cabin. Fire, 8(11), 446. https://doi.org/10.3390/fire8110446

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