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Accident causation models mainly answer the following two questions: (ⅰ) why does an accident occur, and (ⅱ) how does it occur? These models are the most important theoretical basis for safety science, and provide an important method for accident analysis and prevention. To understand accident causation models systematically and comprehensively, this work clarifies the development history of these models over the past 100 years. The work conducted in this study is summarised as follows: (i) The role and origin of accident causation models are introduced. (ii) A new method for classifying accident causation models is proposed. The method divides the accident causal models into linear and nonlinear accident causation models, and the latter are further divided into human-based, statistics-based, energy-based, and system-based accident models. (iii) A review of 29 representative accident causation models proposed in the past 100 years is conducted. The theoretical basis, application flow, and application status of these models are highlighted. (iv) A detailed introduction to the 24Model, an accident causation model with theoretical innovation and more modern safety management, is presented. (v) A comparative analysis of various accident causation models and their development trends are discussed. (vi) This safety also summarises the application status of the accident causal model and prospects for future applications. The research findings of this study are as follows: (i) The newly proposed classification method of accident causation models clarifies the classification of accident causes. (ii) Each type of accident causation model has its own characteristics and application scope. In an accident analysis, an accident model that meets its industry characteristics should be selected. (iii) ‘Organisational factors’ will be replaced by more modern ‘safety management systems’, and people will pay more attention to the role of ‘safety culture’ in accident prevention. Accident causation models will develop in a linear and systematic way. (iv) The current accident causation models consist mainly of qualitative analysis and quantitative analysis, and will develop in the direction of dynamic analysis, accident prediction, and intelligent comprehensive analysis in the future.

Coal is an important energy resource internationally. However, accidents have severely restricted the clean and safe production of coal resources. Among such accidents, coal and gas outburst accidents are a kind of coalmine disaster with high destructive power. Previous research on coal and gas outburst accidents mainly focused on gas factors but ignored the role of human factors. This paper analyses the coal and gas outburst accidents in China from 2008 to 2018 and studies its macroscopic laws. To better understand the causes of coal and gas outbursts, this paper uses the 24modelel to analyse coal and gas accidents and suggest measures for accident prevention from the two aspects ‘gas’ (risk control) and ‘humans’ (behavioural safety). Macroscopic law research found the following: (1) March, May, July, and August are the predominant months for accidents. (2) The second to fourth hours of the working hours and the first hour before the end of work are the peak periods for accidents. (3) Guizhou, Hunan, Henan, Sichuan, Yunnan, and Chongqing are the provinces with the most coal and gas outburst accidents. (4) An overall 75.82 % of accidents occurred in the driving face, and 81.08 % of accidents occurred in coal and gas outburst mines. (5) Blasting, drilling, driving, and coal falling are the main inducing factors. Case analysis of accidents found the following: (1) Human error is the leading cause of accidents. Among the errors, the lack of strict enforcement of outburst prevention measures, illegal command, and the illegal operation of miners are the main unsafe acts. (2) Safety knowledge and awareness of miners is not generally high, and serious habitual violations and unsafe psychologies exist. (3) The gas comprehensive prevention system and supervision system in the coal mine safety management system (SMS) can be easily operated improperly, and the safety training system and emergency management system can be absent. (4) Coalmine enterprises seriously lack safety culture.

Accident prevention depends on accident analysis. In order to improve the reliability of accident analysis and find the common problems related to reliability in accident analysis, two groups of four papers of master’s and doctor’s theses which applied 24Model to analysis coal mine gas explosion accident were selected as samples. The unsafe act results obtained from the analysis are compared. The results show a low consistency level, which reflects that the reliability of the output needs to be improved. Through analysis, the inconsistency of details in causes description, the difficulty in the cause description and the omission of unsafe acts are the main reasons leading to the above situation. In order to standardize the description of cause items, the components of unsafe acts were defined as “premise + action”, and seven types of premises were summarized to judge unsafe acts. In order to improve the efficiency and reliability of accident analysis, it is suggested that the current data should be taken as reference, and the taxonomy based on consequences should be established to unify unsafe act detail description level, and the corresponding computer software should be developed to assist accident analysis.

We propose and demonstrate a high repetition-rate passively mode-locking Tm-doped fiber laser. Mode-locking operation is achieved by using a conventional nonlinear polarization rotation (NPR) structure. Fundamental frequency soliton laser is obtained with the repetition-rate of 5.05 MHz and the pulse width of 54.7 ps. 3-dB bandwidth and signal and noise ratio (SNR) are 3.1 nm and 53.03 dB, respectively. In order to improve repetition-rate of the mode-locking pulse, a narrow band filter is adopted. In this case, maximum repetition-rate of the output pulse can be up to 7.75 GHz (1534 orders). Pulse width and 3-dB bandwidth of mode-locking laser are compressed to 67.2 ps and 0.2 nm, respectively, and SNR is 19.71 dB. In addition, the laser center wavelength can be tuned from 1882 nm to 1925 nm by adjusting the filter.

2- μ m fiber lasers are of wide potential applications in the fields of radar, sensing, and free-space communications. We introduced a simple approach to generate passively mode-locked pulse in thulium-doped fiber lasers based on nonlinear polarization rotation (NPR) in our previous work. The high repetition rate of 1.78 GHz is obtained by both NPR and semiconductor saturable absorption mirror. By using a polarization-maintaining fiber in the experiment, a birefringence Lyot filter as a fiber comb filter can be constructed, and then the tuning range of 94 nm can be obtained for the mode-locked laser. In this paper, we also demonstrated our recent research work, a square-wave mode-locked fiber laser at 2- μ m band based on nonlinear amplifying loop mirror. The square-wave noiselike pulse (NLP) at longer wavelength of 2- μ m band can be observed. With the increase of the pump power, pulse width can be increased from 0.75 to 1.3 ns. The polarization vector characteristics of the square-wave NLP were analyzed experimentally. In addition, with the increase of the pump power, a kind of square-wave mode-locked pulse with low-intensity multipulse bunches can be observed, and these multipulse bunches can be operated at the multipulse mode-locked state. The side-mode suppression ratio decreased from 50 to 30 dB.

In the present study, the Eastern Star ferry accident was analyzed via 24Model. 24Model, as an accident causation model based on system thinking, holds that all causations of the accident are hazards and all hazards in the system need to be identified and comprehensively controlled in accident prevention. The result showed that five factors were the main causes of the accident. First, the direct causes: bad weather, the bad condition of the hull and the unsafe acts of the captain. Second, the indirect cause: the lack of safety awareness and safety knowledge of both the captain and the company’s senior management. Third, there were loopholes in safety management system, including the training, supervision and execution of the company. Forth, the root cause: the company didn’t establish a good safety culture. Last, the external causes: the severe market pressure, excessive regulatory authorities with puzzled relations and responsibilities-seriously hindered effective supervision. In order to prevent this kind of accident and to secure shipping system, the shipping companies and the relevant regulatory units should draw lessons from the five factors mentioned above, and take measures to identify and control those hazards.

In this paper, we propose and experimentally study a simple linear cavity multiwavelength Brillouin-Raman fiber laser (MBRFL). The fiber feedback loop which consists of an optical circulator is placed at the end of the dispersion compensating fiber (DCF) to enhance the reflectivity of the Brillouin Stokes waves. As a result, 245 Brillouin Stokes lines with 0.072 nm channel-spacing are generated across the wavelength range of 18.6 nm from 1544.98 to 1563.58 nm when Brillouin pump (BP) is fixed to 1545 nm/−2.94 dBm and a single Raman pump (RP) laser power is set to 718 mW. The output spectrum is reshaped based on Rayleigh scattering by adding 45 km single mode fiber (SMF) in the cavity. The average optical signal to noise ratio (OSNR) about 18 dB has been measured in this structure. A tunable multiwavelength range of 20 nm from 1545 to 1565 nm is obtained. We also demonstrate the influence of BP wavelength and power on MBRFL.

We study a passively mode-locked square-wave pulse (SWP) fiber laser with a nonlinear amplifying loop mirror in the cavity. The net dispersion of the cavity is about 0.68 ps2 and the SWP mode-locked fiber laser can be realized. The peak power of the SWP hardly varies and the pulse duration gets expanded with the increasing pump power. SWPs breaking in the low nonlinear cavity can be observed and the stable dual SWP can be achieved in the experiment. When the total pump power stays at 800 mW, the interval of dual pulses is 41 ns. The widths of dual SWPs are both 1.5 ns. The output power rises linearly with the increasing of the pump power, while the interval of dual SWPs is almost constant. Then, the physical mechanism of the SWP breaking and vector nature of the pulse are analyzed.

A novel approach to generating 40 GHz narrow linewidth frequency-switched microwave signals is proposed and demonstrated. In this scheme, a single-longitudinal-mode (SLM) double-Brillouin-frequency spaced Brillouin fiber laser with dual-ring configuration and unpumped erbium-doped fiber (EDF) is used to generate dual-wavelength lasers, and a fiber Bragg grating is used to select the laser for different Brillouin frequency spacings. Dual-ring configuration and unpumped EDF are designed to select the mode for the SLM laser. Dual-wavelength lasers are inserted into a photodetector, and microwave signals at 10.66, 21.39, 32.12, or 42.85 GHz can be obtained. The linewidth of the generated microwave signals is less than 69 kHz. The frequency drift at each frequency is less than 0.83 MHz. The frequency noise and linewidth of Stokes signals are measured, and the linewidth broadening effect of microwave signals is analyzed.

We demonstrate a tunable multi-wavelength thulium-doped fiber laser (TDFL). A Sagnac fiber period filter is employed to achieve the tunable multi-wavelength fiber laser and consists of a 3-dB coupler, a segment of 4 m long polarization maintained thulium-doped fiber (PM-TDF) and a polarization controller (PC). Multi-wavelength laser are observed in the wavelength region of 1.9 μm, and the side-mode suppression ratio (SMSR) of the multi-wavelength fiber laser is over 55 dB with 1 W pump power at 1.56 μm. By adjusting PC, tunable range of output laser spectrum from 1955 to 1962 nm can be obtained with single-wavelength laser. In addition, the linewidth of the laser is narrower due to the use of a fiber loop for suppressing multimode oscillation. This fiber laser around 1.9 μm wavelength are useful mid-infrared laser generation, free space laser communications, medicine and biomedical, coherent laser radar for remote atmospheric sensing, pump for nonlinear frequency conversion based on soliton self-frequency shift and second-harmonic generation.

In this paper, a pulse width compression scheme for optical time division multiplexing (OTDM) system based on supercontinuum (SC) is proposed. After injecting a high power narrow line-width pulse width laser into high nonlinear fiber (HNLF), the pulse width has been obviously narrowed. This demonstration suggests that the pulse width compression effect of SC could be used in free-space OTDM system.

In this paper, a free-space optical (FSO) communication system with supercontinuum source generated by dispersion shift fiber (DSF) from pulsed light modulated by optical switches is designed and constructed. In addition, the experimental results of free-space optical communication between broadband and narrowband light source are compared. Verifying the feasibility of broad-spectrum FSO communication link through atmospheric turbulence can be achieved by reducing the inter-symbol interference caused by excessive noise with addition of adaptive equalizer. The experimental results show that the super continuum can be used as the optical signal carrier, and the signal can be wirelessly transmitted under the space atmospheric channel condition.

We propose and experimentally demonstrate a widely tunable mode-locked thulium-doped fiber laser. The laser can operate at both continuous-wave and mode-locked states at different pump power levels. A classic nonlinear polarization rotation structure is employed to obtain the passive mode-locked laser. A birefringence Lyot filter as a fiber comb filter is used to expand the tuning range. Thanks to the filtering component, the tuning range of the continuous-wave laser can reach 127 nm (1823–1950 nm). The tuning ranges of the single-wavelength and dual-wavelength mode-locked lasers are 94 nm (1835–1929 nm) and 87 nm (1831–1918 nm), respectively, with a 3.085 MHz repetition rate and 75 ps pulse width.

The square-wave pulses in passive mode-locked fiber laser present noise-like feature at both normal square-wave state and step-like square-wave state with nanosecond level. Both the two pulses can stably operate at single-pulse and dual-pulse state.

We propose and experimentally demonstrate a multi-wavelength thulium-doped fiber (TDF) laser based on all-fiber Mach-Zehnder interferometer (MZI) at 1.9 mm. Here a segment of 4 m single-mode TDF is pumped by 1568 nm fiber laser for 2 mm band optical gain. The MZI includes two cascaded 3 dB coupler. A segment of 3.5 m long un-pumped polarization-maintaining TDF and polarization controller (PC) are joined in the ring cavity to suppress the mode competition. Multi-wavelength lasers at 1.9 mm with wavelength number from one to four are obtained by adjusting the PC and the stability of output power of multi-wavelength fiber laser is analyzed.

A temperature sensing system based on a multi-wavelength Brillouin fiber laser (MBFL) is proposed and demonstrated. Two beams of Stokes light are generated in a temperature sensitive fiber and a reference fiber, respectively. Stokes light from temperature sensitive fiber can generate frequency shift with temperature changing, and two beams can produce a microwave signal by beat frequency. Therefore, change of temperature can be accurately measured according to variation of the central frequency of the beat frequency microwave signals. A 3.2 km long dispersion shifted fiber (DSF) is used as temperature sensitive fiber pumped by a Brillouin pump with power of 1.5 W, then more than 20 Stokes light wavelengths can be observed. By using the 18th order Stokes light pair, temperature sensitivity can be 19.93 MHz∕°C. The uncertainty of the temperature measurement is ± 0.125°C.

We demonstrate a square-wave soliton pulse passively mode-locked fiber laser. The mode-locked pulses are achieved by using a nonlinear amplifying loop mirror. Single-pulse operation at a fundamental repetition rate of 3.2 MHz is obtained. The optical spectrum presents the soliton feature of several sidebands. The pulse duration expands with increasing pump power, but the amplitude hardly varies. Pulse breaking occurs and a stable dual-pulse is obtained with a fixed interval of 48 ns. Harmonic mode-locked states can be achieved when the total pump power is higher than 740 mW. The harmonic pulses can also operate in both single-pulse and dual-pulse states.

We experimentally studied a passive mode-locked square-wave fiber laser with net-normal dispersion by using a nonlinear amplifying loop mirror. The output pulse width of the square-wave pulse (SWP) can be extended with the increasing of the pump power as well as single pulse energy. The SWP can be amplified without shape distortion when the mode-locked laser is injected into an erbium-ytterbium codoped fiber amplifier. Then, by inputting the amplified SWPs into a single mode fiber (SMF), a supercontinuum (SC) can be observed with the spectral range of about 1550 to 1850 nm. Broader and flatter SC with the 20-dB spectral range of about 1550 to 1950 nm can also be generated using a segment of dispersion-shifted fiber instead of SMF.

A tunable multi-wavelength Brillouin fiber laser with double Brillouin frequency spacing based on a four-port circulator is experimentally demonstrated. The fiber laser configuration formed by four-port circulator isolates the odd-order Brillouin stokes signal to circulate within the cavity only. In addition, it also allows propagation of the incoming Brillouin pump and even-order Stokes signals from four-port circulator to output coupler .A L-band erbiumdoped fiber (EDF) with 1480nm pump is used to amplify Stokes signals and to get more output channels. At the Brillouin pump power of 8dBm and the 1480 nm pump power of 200mw, 5 output channels with double Brillouin frequency spacing and tuning range of 20 nm from 1568nm to 1588nm are achieved.

In this paper, a segment of thulium-doped fiber is pumped by a 976nm laser diode.Broadband gain at centerwavelength of 1953nm is achieved. The maximum amplified spontaneous emission bandwidth is 8nm. Simultaneously, self- oscillation of wavelength spacing 0.073nm is observed. The output power and self- oscillation modes increase with pump power increasing and wavelength spacing of self-oscillation is unchanged.The relation between fiber length and output power at pump power 400mW is analyzed. Higher output power can be abtained by selecting a appropriate fiber length when pump power is unchanged. Through the experiment, a weak absorption band of thulium-doped fiber near 976nm is verified. The structure can be used as narrow linewidth broadband source near 1950nm with the characteristic of low cost, simple structure and good stability.

A dual-wavelength linear cavity erbium-doped fiber (EDF) laser based on a fiber grating pair is demonstrated experimentally. A circulator, a 980nm/1550nm wavelength division multiplexing (WDM) coupler, a 1×2 coupler, a polarization controller, a 6m long erbium-doped fiber and a fiber grating pair for wavelength interval of 0.3nm are included in the structure. A circulator connected at two ports as reflecting mirror structure. A 980nm pump source pump an erbium-doped fiber with a length of 6m consist of an erbium doped fiber amplifier. Through adjusting the state of the polarization controller, the transmission characteristic of cavity is changed. In both polarization and wavelength, the feedback from the fiber grating pair results in the laser operating on two longitudinal modes that are separated. The birefringence induced by the fiber grating pair is beneficial to diversify the polarization states of different wavelength in the erbium-doped fiber. So it is enhanced the polarization hole burning effect. This polarization hole burning effect greatly reduced the wavelength competition. Then, it was possible to achieve stable dual-wavelength. It turns out the structure generated the stable dual-wavelength with the 0.3nm wavelength interval and the output power is 0.13dBm in the end. The whole system have a simple and compact structure, it can work stably and laid a foundation for microwave/millimeter wave generator. It has a good application performance in the future for scientific research and daily life.

A Brillouin-Erbium multi-wavelength tunable fiber laser at C-band is demostrated. A 10 km long singlemode fiber(SMF), a 6 m long Erbium-doped fiber, two couplers, a wavelength division multiplexer, a isolator, an optical circulator, a 980nm pump laser and a narrow linewidth tunable laser are included in the structure. A segment of 10 km-long single-mode fiber (SMF) between the two ports of a 1×2 coupler is used as Brillouin gain. Ebiumdoped fiber amplifier（EDFA） consists of a segment of 6m er-doped fiber pumped by 980nm laser dioder . A narrow linewidth tunable laser from 1527 to 1607 nm as Brillouin bump, At the Brillouin pump power of 8mW and the 980 nm pump power of 400 mw, 16 output channels with 0.08 nm spacing and tuning range of 40 nm from 1527 nm to 1567 nm are achieved. We realize the tunable output of wavelength by adjusting the 980 nm pump power and the Brillouin pump wavelength. Stability of the multiwavelength fiber laser is also observed.

We propose and experimentally investigate a multiwavelength Brillouin fiber laser (MBFL) with triple frequency spacing by employing a modular structure. In this scheme, we obtain nine channels optimized with frequency spacing of 0.259 nm. The single, double, and triple Brillouin frequency spacing for the MBFL can be easily realized by utilizing this modular structure. The impact of Brillouin pump (BP) power, BP wavelength, and erbium-ytterbium-doped fiber amplifier (EYDFA) output power on the performance of the MBFL is investigated, respectively. We also study the generation of beating frequency microwave signals based on single, double, and triple frequency spacing MBFL. 10.5 GHz, 21.48 GHz, and 31.77 GHz microwave signals with 3 dB linewidth of 16.4 MHz, 15.2 MHz, and 12.8 MHz are generated, respectively.

A simple approach to generate passively harmonic mode-locked pulse trains in thulium-doped fiber laser based on nonlinear polarization rotation is proposed and demonstrated. Three different ways of mode-locked techniques have been employed in our structure to generate passively high-order harmonic mode-locked pulse trains; 128th-order passively harmonic mode-locked pulse train is achieved in the experiment and the repetition rate is 406.8 MHz. With the increase of the pump power, multiwavelength output can be tuned. A segment of dispersion compensation fiber is used to compensate the dispersion in the cavity; thus, the single pulse width is compressed from 617 to 48 ps.

An ultra-narrow linewidth multiwavelength Brillouin fiber laser is demonstrated. Erbium-doped fiber amplifier with linear gain is not used in the structure to avoid the signal broaden. Multiwavelength output with identical interval and ultra-narrow linewidth will be obtained through the experiment. Because the whole system works with a simple structure, it can work stably and has a good application performance in the future. A one-way feedback multiwavelength Brillouin fiber laser structure has been designed. A 2x2 3dB coupler, a 8 km-long single-mode fiber (SMF), a distributed feedback(DFB) semiconductor laser and two optical circulators are included in the structure. A segment of 8 km-long single-mode fiber (SMF) between the two ports of a 2x2 3 dB coupler is used as Brillouin gain loop. A distributed feedback semiconductor laser works as the Brillouin pump (BP). Laser output and feedback are realized by two optical circulators. We adopt the Brillouin pump power at 80 mW. Seven Stokes signals can be observed excluding BP. The Brillouin frequency shift is 0.088 nm compares with the wavelength of BP. We have measured multiwavelength Brillouin fiber laser spectrum ten times in 50 minutes. The experiment result shows that the multiwavelength output of Brillouin fiber laser is very stable. The 3 dB linewidth of the output laser is 5 kHz measured by the frequency spectrum analyzer.

We demonstrate a multi-wavelength fiber laser with Brillouin cavity loop. Brillouin-Erbium fiber laser (BEFL) integrates Brillouin and Erbium gains in the resonate cavity to produce high power multi-wavelength fiber laser. The Brillouin gain loop connects with main ring cavity by port2 of the circulator1. A coil of SMF with a length of 10 km is employed by 3-dB fiber coupler as Brillouin gain medium, and pumped by Brillouin pump (BP), a tunable laser with a maximum output power of 15 dBm to generate Stokes light. The measured results were extracted from the laser system by using 90/10 coupler where 10% power is used for monitoring and measurement purpose while the 90% power is feedback into the laser cavity. A 1550 nm tunable laser diode (LD) provided the BP that can be tuned from 1470 nm to 1580 nm (110 nm tuning range). Two fiber circulators are used as the fiber reflection loops at both ends of the linear cavity. The effect of the erbium-doped fiber amplifier (EDFA) locating at different locations in the cavity BEFL on Stokes wave is experimentally studied. In the experiment, with EDFA in position A, the tunable range and the output power of the multi-wavelength laser were limited by gain saturation of the signals and the self-lasing cavity modes. The self-lasing cavity modes were suppressed without EDFA, but the tunable wavelength range was narrower because of the low gain. By using EDFA at the total reflective side of the linear cavity, more Stokes waves and wider tunable range was observed because the more powerful Stokes feedback light was amplified twice by the EDFA. The peak power of -1.8dBm and the tuning range of 60 nm were obtained. It has many important applications, such as dense wavelength division multiplexing (DWDM) systems, distributed fiber sensing, slow light, and microwave photonics, etc.

We demonstrate a distributed feedback (DFB) random fiber laser based on Rayleigh scattering. Amplified spontaneous emission is produced by using a segment of erbium doped fiber (EDF) pumped by 980 nm laser diode (LD). An 50km-long single-mode fiber (SMF) and a fiber bragg grate (FBG) are used as random resonate cavity and wavelength output at 1550 nm is observed which can be amplified through the erbium-doped fiber amplifier. Evaluations on the spectral evolution and power development are also performed from the results obtained.

A simple photonic approach to generate microwave frequency switched microwave signal is proposed and experimentally demonstrated. In this scheme, a Brillouin fiber laser with double-Brillouin-frequency spacing is used. The Brillouin ring configuration suppresses incoming Brillouin pump and even-order Stokes signals in the cavity. In addition, it also allows propagation of the odd-order Brillouin Stokes signals from configuration to output coupler. A dual-wavelength optical signal is heterodyned at the high-speed photodetector to produce a microwave signal. Frequency switched microwave signals, at 10.75 and 21.39 GHz, respectively, can be obtained through adjusting the polarization controller (PC) and loss of the variable optical attenuator (VOA).