Noise evaluation in oil and gas fields and associated risk assessment

This work investigates the noise levels in oil and gas fields and their impact on the health of operators, visitors, and trainees in these workplaces, as well as possible methods of maintaining that noise within acceptable levels. A risk assessment was performed to identify the noise hazards associated with particular activities or tasks in oil and gas fields. A case study focusing on sulfur recovery units (SRUs) at a gas processing complex consisting of three production plants was carried out. Many master points in these plants where workers present were selected at random. In order to accurately measure the noise level at each point, it was measured at different times during the period 2014–2017 and compared with the maximum safe noise level defined by OSHA (85 dB). Results show that most of the noise levels encountered in the field are above the maximum level. An Ishikawa diagram was created to analyze the causes and effects of excessive noise in the field. Causes included rotating machines, maintenance activities, steam leakages, fluid flows, and gas flares. Finally, the results of the risk assessment indicated that oil and gas fields can present high noise risk scores, implying that workers in those fields could be harmed by the noise.


Introduction
Noise is defined as unwanted sound (Wright and Atmoko 2001). Noise pollution is one of the important forms of pollution encountered in workplaces, and can be one of the most harmful to workers (Arefian et al. 2008). In particular, noise pollution can result in damage to the auditory sensory mechanism, potentially leading to a premature and permanent loss of hearing (Aluclu et al. 2008).
The general effect of noise on the hearing of workers has been a topic of debate among scientists for a number of years (Jansen 1992). Various regulations limiting the exposure of industrial workers to noise have been instituted. For example, OSHA (the Occupational Safety and Health Administration) has published occupational noise exposure regulations which state that industrial employers must limit the noise exposure of their employees to 85 dB (decibels) (USEPA 1973), as exposure to continuous and extensive noise at levels higher than this may lead to hearing loss. The likelihood of continuous hearing loss differs depending on the worker exposed, the noise level, the frequency of the noise, and duration of the noise (USEPA 1974). For instance, much of the equipment used in the lawn care industry produce noise levels louder than the recommended 85 dB: the noise level of a lawn mower is 101 dB; that of a leaf blower is 110 dB; and that of a chainsaw is 120 dB (Center for Hearing and Communication 2013).
The damage to the inner ear caused by noise or vibrations encountered during certain types of occupations or entertainment is known as occupational hearing loss (Zieve 2010). Negative effects of noise on human beings are generally physiological and/or psychological in nature. Hearing loss is the most common physiological effect. It is possible to classify the effects of noise on the ears into three groups: acoustic trauma, temporary hearing loss, and permanent hearing loss (Melamed et al. 2001). Increased blood pressure, accelerated heart beat, and specific muscle reflexes have also been observed as a result of noise exposure. The vast majority of industrial workers are exposed to noise (Cheung 2004 In this study, the levels of noise exposure of workers in oil and gas fields were investigated and compared with the maximum safe noise level defined by OSHA. In this context, measurement of noise is done at different period of time called discrete field data. The sources of potentially harmful noise were analyzed using an Ishikawa diagram (which presents the causes and effects of a particular event). Moreover, a risk assessment was performed to determine the level of risk presented by the noise to workers.

Study area
This work focused on noise levels in the Western Libyan Gas Project, a joint venture between the Libyan National Oil Cooperation and the gas company Eni. In 2005, The Libyan Ministry of Energy reported that this project was Libya's most ambitious nonassociated gas project, and that it expected the first flow generated by this project in 2005 to mark a significant change in the Mediterranean Sea, as the $6.4 billion that was invested in the project would lead to the generation of about 2 billion barrels of oil. The Bouri Oil Field has held pride of place since the 1980s as the premier oil field off the coast of Libya. The Western Libyan Gas Project extracts from two offshore fields, Bahr Essalam and the Sabratha Platform, and from two onshore fields, the Wafa Field and the Mellitah Complex (Fig. 1). These fields produce approximately 30 million Sm 3 /day of gas, 60,000 barrels/day (b/d) of oil/condensate, 15,000 b/d of liquid propane and butane, and 500 tons/day (t/d) of sulfur. Three gas plants are located in the Mellitah Complex; these plants are connected to three sulfur recovery units (SRUs) via a common acid gas header. The main function of these SRUs is to treat the sour gas from the gas plants, which contains CO 2 , H 2 S, water, and traces of hydrocarbons (HCs) (Mellitah Oil and Gas B.V. 2006). The sour gas is fed to a H 2 S enrichment unit to increase the H 2 S concentration, and the resulting amine acid gas (AAG) is fed to a Claus unit, where the H 2 S is converted into sulfur.

Field work
Sound is measured in decibels (dB) using sound level meters. These meters measure the pressure of the sound waves. The noise-measuring meter used in this survey was a RION NL 52 sound level meter that has a range of 30-130 dB and is compliant with the Occupational Safety and Health Act of 1970 (OSHA). The OSHA noise standard used in this survey is summarized in Table 1. Table 2 shows the likelihood that a noise event of a particular sound level will occur according to the field data measured in this study. This likehood ranged from "very likely" to   Table 3 shows how the severity of the effect of noise on a human depends on the sound level of the noise. The impact rating used in this study was based on this effect severity of the noise, and was divided into five categories ranging from "very low" to "extreme," which corresponded to impact ratings of 1 and 5, respectively.

Risk assessment
Applying these likelihood and severity methods to the results of the field studies yielded a risk matrix. The relative risk was calculated as the product of the probability rating and the impact rating. The recommended action linked to each risk score is shown in Table 4. The higher the score obtained by multiplying the likelihood and severity ratings, the higher the risk level.

Results and discussion
Based on the field data collected for three sulfur recovery units (Plant1, Plant2, and Plant3), a gas processing plant (Plant4), and a steam turbine (Plant5), noise surveys were performed for those plants. Figure 2 shows the noise levels at various master points around one of the sulfur recovery units, Plant1. It is clear from the figure that the noise levels at all the master points in the plant often exceeded the level (85 dB) that is capable of damaging hearing; OSHA standards recommend that workers should not be exposed for long periods to noise exceeding this level.
Similarly, Figs 3, 4, 5, and 6 show that the noise levels at different master points around Plant2, Plant3, Plant4, and Plant 5 tend to be above the maximum level recommended by OSHA (85 dB). A risk assessment of the field data on noise levels indicated that the high probability of excessive noise generation by gas processing operations and the impact of such noise may present health risks to workers. As a result of risk assessment, risk register is showing the risk rating of noise levels in the area. Table 5 isillustrated the risk rating, in which the risk was high at 85-100 decibel and over than 100 decibel, medium in 50-85decibel and low for lower noise level (less than 50 decible). Figure 7 presents the Cause and effect analysis which was used to analyze the sources and effects of the excessive noise in the areas considered. An Ishikawa diagram was created and used as an analytical tool. As shown in the diagram, the excessive noise in the plants is generated by fluid flows, rotating machines, maintenance activities, steam leakages, and gas flares.

Conclusion and recommendations
The noise surveys performed in this work showed that sulfur recovery units are associated with high levels of noise that tend to exceed the OSHA-recommended maximum noise level of 85 dB. An Ishikawa diagram indicated that the main sources of excessive noise in the sulfur recovery plants are   2 Noise levels at the master points around Plant1 (a sulfur recovery unit); the OSHA-recommended safe limit for noise is also plotted Fig. 3 Noise levels at the master points around Plant2 (a sulfur recovery unit); the OSHA-recommended safe limit for noise is also plotted Fig. 4 Noise levels at the master points around Plant3 (a sulfur recovery unit); the OSHA-recommended safe limit for noise is also plotted steam leakages, pressure safety valves, vibrations of fluid flows, flares, and rotating machinery such as compressors, pumps, and fan coolers. Loud noise can also be generated during maintenance activities such as hammering and welding. These excessive noise levels can exceed the pain threshold of workers at oil and gas facilities, and can rupture their eardrums and cause hearing damage. Finally, the excessive noise generated by oil and gas facilities is also a health risk because it can increase the likelihood of accidents. Therefore, Its highly recommended to mitigate the potential health effects of excessive noise by reducing the exposure times of workers, using PPE (personal protective equipment), modifing processes, re-engineering practices, and reducing noise levels.

Fig. 5
Noise levels at the master points around Plant4 (a gas processing plant); the OSHA-recommended safe limit for noise is also plotted Fig. 6 Noise levels at the master points around Plant5 (a steam turbine); the OSHA-recommended safe limit for noise is also plotted