Author(s): Zhao Yun*, Bao Jinling, Guo Jian, Tang Haiqi, Song Hui, Wei Yan, Chen Zhijun, and Xu Yiping
The purpose of this study is to investigate the hazard status of benzene and hydrogen sulfide in a crude oil depot and evaluate the occupational health risk level, so as to provide counter measures for risk control. In this study, the comprehensive index method was used to evaluate the occupational health risk level of exposure to benzene and hydrogen sulfide in the pump room, valve group, control room and tank metering port. The results show that the metrology workers are exposed to benzene and hydrogen sulfide in the process of operation of pump room, valve group, control room and tank metering port. Sanitary engineering protection measures are mainly closed operation, and set up ventilation fan in the pump room, personal protective equipment is mainly anti-static work clothes, oil-resistant gloves, respiratory protective equipment is gas masks, but they are not weared daily. The occupational health management system is complete. The working time of each shift is 12h, with a maximum of four shifts per week for 48h and a maximum of 12h per shift for exposure to chemical hazardous agents. Benzene and hydrogen sulfide were tested for 11 samples each, and the detected exposure concentration was not exceeding the standard. The hazard levels of benzene and hydrogen sulfide were grade 5 and grade 4, respectively, and the exposure level was 1.62. The risk index of exposure to benzene and hydrogen sulfide was 3, and the risk level was medium. The protective measures for the crude oil depot are effective, but the on-site monitoring of benzene and hydrogen sulfide concentration should be strengthened to prevent acute poisoning accidents and reduce occupational health risks.
Crude oil depot is an important place for the storage and turnover of crude oil. The trace evaporation of crude oil in the daily storage process may cause a certain degree of occupational health hazard to workers. Crude oil contains benzene, hydrogen sulfide and other chemical hazardous agents. Benzene belongs to grade one carcinogen [1]. Long-term inhalation of benzene will affect the nervous system of the victim. Hydrogen sulfide is an acute poison that can be fatal in a short time if inhaled in small amounts and in high concentrations. Low concentrations of hydrogen sulfide affect the eyes, respiratory system and central nervous system. In view of the high harm of benzene and hydrogen sulfide and the large stock of crude oil depot, it is necessary to evaluate the occupational health risk of benzene and hydrogen sulfide in crude oil depot. Occupational health risk assessment is a process of qualitative or quantitative assessment of occupational health risk level through comprehensive and systematic identification and analysis of workplace risk factors and protective measures, so as to adopt corresponding risk control countermeasures [2,3]. In order to understand the occupational health risk status of the crude oil depot staff’s exposure to benzene and hydrogen sulfide, this study intends to use the comprehensive index method to carry out a semi-quantitative assessment of the occupational health risk of an crude oil depot, so as to provide a basis for the corresponding risk control measures.
Research objects and methods Research objects & Crude Oil Depot
Methods
Occupational health survey
Occupational hygiene survey was carried out on the crude oil
depot, including the working position, working shift system,
exposure to benzene and hydrogen sulfide, protective facilities
for sanitary engineering, personal protective equipment and
occupational health management measures.
Detection of chemical hazardous agents
Time weighted average concentration (C TWA ) of benzene in the
air of crude oil depot was measured by sampling according to the
requirements of GBZ159-2004 “Sampling Standard for Monitoring
Hazardous Substances in Workplace Air” and GBZ/T 160.33-2004
“Determination of Sulfide in Workplace Air Toxic Substances”.
In accordance with the requirements of GBZ/T 300.66-2017
“Determination of Toxic Substances in Workplace Air - Part 66:
Benzene, Toluene, Xylene and Ethylbenzene”, samples were
taken to determine the maximum concentration (CM
) of hydrogen
sulfide in the air of the crude oil depot. According to GBZ 2.1-
2019 “Occupational exposure limits for hazardous factors in the
workplace - part 2: chemical hazardous factors”, the permissible
concentration-time weighted average of benzene (Occupational
exposure limit (OEL)) is 6.00mg/m3
, and the maximum allowable
concentration of hydrogen sulfide (Occupational exposure limits)
is 10.00mg/m3
1.2.3 Semi-quantitative risk assessment by comprehensive index method [4]. The Exposure index (EI) was determined by considering the hazard characteristics, hazard control measures, Exposure time and Exposure level of benzene and hydrogen sulfide. The Exposure risk (ER) was calculated according to formula (1), and the risk level (risk, R) was calculated according to formula (2) [GBZ/ t298-2017]. In this study, when R value is 1, 2, 3, 4, and 5, R is negligible risk, low risk, medium risk, high risk, and very high risk , respectively.
(1) Where: ER - exposure level; EI - exposure index is divided into 5 levels according to the increase of exposure dose; n - number of exposure factors (2) Where: R - risk level; HR -- hazard level; ER - level of exposure.
The results of the study
Basic situation
The crude oil depot is mainly engaged in loading, unloading
and storage of crude oil. The metrology work mainly includes
starting and stopping of pump and inspecting operation, inspecting
operation of valve group and pipeline, monitoring operation
of control room and inspecting operation of storage tank. The
working time of each shift is 12h, with a maximum of four
shifts per week and a maximum of 48h. The time of exposure
to chemical hazardous agents in each shift is 12h. Workers
are exposed to benzene and hydrogen sulfide mainly through
respiratory exposure, with occasional skin exposure. The crude
oil is transported in closed pipelines and stored in closed tanks.
The pump room is equipped with a ventilator for ventilation and
normal operation; Personal protective equipment is mainly anti-
static work clothes, oil-resistant gloves, respiratory protective
equipment is a gas mask, but do not wear daily; The occupational
health management system is complete.
Hazard identification
The main chemical hazardous agents of volatile components of
crude oil are benzene and hydrogen sulfide. Crude oil volatilizes
slowly in the valve and pump room of the pipeline. When the tank
metering port of the storage tank is opened, the crude oil vapor
in the storage tank volatilizes into the air along the tank metering
port. This can lead to exposure of site operators to benzene and
hydrogen sulfide hazards.
Hazard characteristic assessment
According to the toxicity of the chemicals, the harm of benzene
and hydrogen sulfide was classified, and the hazard levels were
rated as grade 5 and grade 4 respectively.
Exposure assessment
Detection results
The concentrations of benzene and hydrogen sulfide were detected
in four places: pump room, valve group, control room and tank
metering port. A total of 11 samples were tested for benzene, with
the detection range of detected exposure concentration ranging
from 0.03 to 1.6mg/m3
, and the CTWA of the pump room, valve
group, control room and tank metering port were 0.67, 0.03,
0.03 and 1.05mg/m3
, respectively, with no places exceeding the
standard. Hydrogen sulfide was detected in 11 samples, with
the range of detected exposure concentration ranging from 0.53
to 1.81mg/m3
, and the detected exposure concentration (C M ) of
hydrogen sulfide in the metrometer was 0.74, 0.53, 0.53 and
1.32mg/m3, respectively. The detection results of meterobenzene
and hydrogen sulfide is shown in table 1.
Table 1: detection results of benzene and hydrogen sulfide in a crude oil depot workplace
| chemical hazardous agents | Sample numbers | detected exposure concentration (mg/m3) | Number of exceeded samples | ||
|---|---|---|---|---|---|
| range | CTWA | C M | |||
| benzene | |||||
| pump room | 3 | 0.6~0.7 | 0.67 | - | 0 |
| valve group | 3 | 0.03 | 0.03 | - | 0 |
| control room | 3 | 0.03 | 0.03 | - | 0 |
| tank metering port | 2 | 0.5~1.6 | 1.05 | - | 0 |
| hydrogen sulfide | |||||
| pump room | 3 | 0.53~0.92 | - | 0.74 | 0 |
| valve group | 3 | 0.53 | - | 0.53 | 0 |
| control room | 3 | 0.53 | - | 0.53 | 0 |
| tank metering port | 2 | 0.83~1.81 | - | 1.32 | 0 |
Exposure ratio
The exposure concentration (E) was estimated according to the exposure time of 48h per week, and E was compared with the
corresponding Occupational exposure limit (OEL, the permissible concentration-time weighted average of benzene, and the maximum
allowable concentration of hydrogen sulfide). The exposure ratio of benzene and hydrogen sulfide (E/OEL) was calculated respectively.
The results of the exposure ratio calculation are shown in table 2.
Table 2: contact ratio of exposure to benzene and hydrogen sulfide of metrology workers
| chemical hazardous agents | Weeklyexposurefrequency(d/w) | Time perexposure(h/d) | detectedexposureconcentration(mg/m3 ) | Weeklyworkinghours(/w) | E(mg/m 3 ) | OEL | E/OEL |
|---|---|---|---|---|---|---|---|
| benzene | |||||||
| pump room | 4 | 3 | 0.67 | 48 0.28 4.69 0.06 | |||
| valve group | 4 | 2 | 0.03 | ||||
| control room | 4 | 6.5 | 0.03 | ||||
| tank metering port | 4 | 0.5 | 1.05 | ||||
| hydrogen sulfide | |||||||
| pump room | 4 | 3 | 0.74 | 48 8 0.73 10 0.07 | |||
| valve group | 4 | 2 | 0.53 | ||||
| control room | 4 | 6.5 | 0.53 | ||||
| tank metering port | 4 | 0.5 | 1.17 | ||||
Note 1: The personnel in the pump room, valve group, control room and tank metering port are all metrology workers. The weekly exposure concentration of metrology workers is the sum of the weekly exposure concentration of the four sites;
2. The occupational exposure limit of benzene is a permissible concentration-time weighted average , which is multiplied by a reduction factor
Exposure index classification
The exposure index is mainly determined by the vapor pressure of the chemical hazardous agents, the exposure ratio (E /OEL), the
occupational-disease-inductive measures, the amount used and the exposure time. See table 3.
Table 3: exposure index classification of exposure to benzene and hydrogen sulfide
| chemical hazardous agents | vapor pressure | E/OEL | Hazard control measures | weekly amount | weekly exposure time | ER | ||||
|---|---|---|---|---|---|---|---|---|---|---|
| sanitary engineering protection |
emergency rescue facility |
personal protective equipment |
Emergency rescue measures |
management system | ||||||
| benzene | 1 | 1 | 1 | 1 | 5 | 1 | 1 | 3 | 5 | 1.62 |
| hydrogen sulfide | 1 | 1 | 1 | 1 | 5 | 1 | 1 | 3 | 5 | 1.62 |
Description of risk characteristics
According to the hazard level and exposure level of benzene and hydrogen sulfide, the risk index was calculated and the risk level
was determined. The decision results are shown in table 4.
Table 4: occupational health risk levels of metrologers in a crude oil depot
| chemical hazardous agents | HR | ER | risk index | risk level |
|---|---|---|---|---|
| benzene | 5 | 1.62 | 3 | medium risk |
| hydrogen sulfide | 4 | 1.62 | 3 | medium risk |
Discussion
In this study, the occupational health risk assessment of benzene
and hydrogen sulfide in crude oil depot was conducted by
comprehensive index method. The personnel exposed to benzene
and hydrogen sulfide hazards in the pump room, valve group,
control room and inspection port are all metrologists, so the
occupational health risks of the above four positions were assessed
in combination.
The results show that the concentrations of benzene and hydrogen sulfide are not exceeding the standard. The reason may be that the pipelines and storage tanks in the crude oil depot are well sealed, and the evaporation amount of benzene and hydrogen sulfide in the crude oil component is also low. The detected exposure concentration of the pump room and the inspection port is relatively high, because the pump room is an indoor environment, and the oil pump is less dense than the oil pipeline, and the crude oil evaporation is relatively large. The metering port leads to the tank, and the crude oil vapor above the original oil level in the tank has a high concentration. When the measuring port is opened, the crude oil vapor diffuses outward, resulting in a high detection concentration of benzene and hydrogen sulfide. Although none of the test results in this study exceed the standard, it is not excluded that the airtight degree of oil pumps, pipelines, valves and other facilities is reduced during use, resulting in higher exposure concentration, and under special circumstances, the crude oil vapor in the storage tank rapidly diffuses through the metering port, resulting in benzene or hydrogen sulfide concentration exceeding the standard.
In recent years, more and more risk assessment techniques have been applied to risk control and management in the workplace [5-7]. Risk assessment includes the analysis and assessment of inherent risk factors and risk offsetting factors [8]. The hazard of benzene and hydrogen sulfide mainly depends on its toxicity, exposure route, and so on. This is the inherent risk factor of chemical harmful factor, cannot eliminate commonly. However, the risks can be eliminated or reduced by means of sanitary engineering protection, occupational-disease-prevention articles, emergency rescue measures and occupational health management. The operation process of the crude oil depot has a high degree of sealing, good protection of health engineering, and a sound emergency rescue plan and occupational health management system are formulated, which can eliminate or reduce occupational health risks to a certain extent. This study result shows that the measurement of workers exposure to benzene and hydrogen sulfide occupational health risk level is moderate, but due to lack of personal respiratory protective equipment, under the condition of the engineering protection failure, may cause the heavier occupational health risks, especially hydrogen sulfide can also cause acute poisoning accident. Since there is a certain risk management weaknesses, it is suggested metrologers should carry gas mask and portable hydrogen sulfide concentration detector, in order to avoid acute poisoning accident and reduce occupational health risks.
References
