Semi-quantitative
risk assessment of health exposure to hazardous chemical agents in a
petrochemical plant
Beheshti MH, MSc1, Firoozi chahak A, MSc2*, Alinaghi Langari AA, MSc3, Rostami S, BSc4
1- Faculty Member, Dept.
of Occupational Health, Faculty of Health, Gonabad University of Medical
Sciences, Gonabad, Iran.
2- Faculty Member, Dept. of Occupational Health, Faculty of Health, Gonabad University of Medical
Sciences, Gonabad, Iran. 3-
Faculty Member, Dept. of Occupational Health,
Faculty of Health, Bam University of Medical Sciences, Bam, Iran. 4- BSc of
Student, Dept.
of Occupational Health, Faculty of Health, Bam University of Medical
Sciences, Bam, Iran.
Abstract
Received:
December 2015,
Accepted: February 2016
|
Background: Chemical
contaminants present in the work environments include gases, vapors, and
solid and liquid suspended particles. The
number of factories producing chemicals has increased significantly. Each
year, new products are introduced into the market. Consequently, the number
of employees at risk of exposure to these materials is increased. Hazardous
chemicals are used in the petrochemical industry that is one of the major
industries in the country's economic development. Therefore, the aim of this
study was a semi-quantitative risk assessment of health exposure to
hazardous chemical agents in a petrochemical plant. Materials
and Methods: This was a descriptive analytical study for assessing
the sanitary risks of hazardous chemical factors in the work
environment through a risk assessment method provided by the Occupational
Health Department of Singapore. Thus, initially, occupational tasks and
processes were determined. Subsequently, all hazardous chemical factors were
detected, and then, the degree of risk, the degree of exposure, and risk
rating were determined. Results: In total,
24 tasks were examined and risk assessment was performed for 19 hazardous
chemical substances in this study. Among these materials, benzene and xylene
had the highest risks and were used in various occupations. In this study,
mean and standard deviation of age and experience of participants were 30.28
± 7.87 and 5.98 ± 5.66, respectively. Moreover, 25.3% of participants in this
study were single and 74.7% were married. Conclusions:
It can be concluded that 81% of chemicals used in this industry are rated
at moderate and high risk. In order to control the identified risks, this
study recommended programs and control measures based on the hierarchy of
elimination, substitution, engineering controls, administrative controls, and
use of personal protective equipment. |
Keywords: Risk Assessment,
Chemicals, Petrochemicals,
Hazardous Chemical
Introduction
Chemicals have many benefits in the present day society
and our contemporary life is completely dependent on them (1). Today, thousands of chemicals are used all over the world (2). Workplace chemical
contaminants include gases, vapors, and solid or liquid suspended particles. Each of these
materials has specific risks, and the effects caused by these materials differ
depending on the type of chemical, route of entry, duration, and density.
Excessive exposure to these materials at work can cause poisoning and a variety
of diseases (3, 4). Some consequences of exposure to chemicals are
instantaneous, but since many of the chemicals are used in low concentrations or the rate of exposure is low,
the effects of exposure are cumulative and will appear in the body over *a
long period of time. Therefore, certain systemic symptoms may not occur in the
short term and symptoms are observed in the long term and they have
consequences such as illness, motion or physical injury, and even death (5).
The number of factories producing chemicals has increased significantly and new
products are introduced into the market each year. Consequently, the number of
employees at risk of exposure to these materials has also increased. Some of
these chemicals are new compounds and mixtures and their toxicological
properties have not been studied previously and they may be dangerous to humans
(6). The World Health Organization (WHO) statistics indicate that 4 million
people worldwide are engaged in the chemical industry, and 1 million people die or are disabled annually
as a result of unsafe exposure to chemicals (7).
The petrochemical industry is one of the important industries that have a
major effect on the country's economic growth. Petroleum products and raw
material required for numerous processes in many other industries are produced
in this industry. Therefore, workers are exposed to various contaminants. The
need for a comprehensive plan to determine hazardous chemicals that effect the
health of individuals exposed to these materials and also hazardous tasks and
processes can be felt today more than ever (6, 8). This can be achieved through
chemical risk assessment. Chemical risk assessment can assist in the
prioritization of hazardous contaminants, and the selection of appropriate
control measures (9). In other words, the risk assessment of chemicals can be a
comprehensive assessment of workers’ exposure to health risk factors and
decisions about anticipated control measures, training of employees,
monitoring, and health care to protect employees against exposure to hazardous
chemicals in the workplace (10). There are several methods for risk assessment,
but methods that are able to assess sanitary risks caused by exposure to
chemicals are rarely considered.
In quantitative methods, epidemiological data is used for
assessing sanitary risks. An example of this is the study of Jafari et al. in
which the relative risk of leukemia due to benzene exposure was calculated. In
qualitative methods, employees’ rate of exposure to occupational hazardous
factors is estimated through determining the degree of risk and exposure using
a risk assessment matrix (8, 11). Due to the lack of national epidemiological
data and the long duration of quantitative methods, a specific and functional
method for risk assessment of occupational exposure to harmful chemical agents
was introduced in this study. Furthermore, we used this method in the
petrochemical industry to determine the exposure level to chemicals and
prioritize control measures to reduce risks to an acceptable level.
Material and Methods
This study was conducted in the operation unit of an Iranian petrochemical company that has the most
variety of pollutants and its workers are exposed to high levels of pollutants.
In total, 24
tasks were examined in this study and ultimately risk assessment was performed
for 19 hazardous chemical substances.
This study was conducted through census method; thus, there was no need to
determine the sample size.
The method of sanitary risk assessment of hazardous chemical agents in the
work environment provided by the Department of Occupational Health in Singapore
was used in this study (12). This approach was implemented in the following
steps:
1.
Formation of working groups:
The members of this working group consist of the supervisor of the operations
unit, an employee representative, an employer representative, and an
occupational health or safety specialist.
2.
Analysis of the process of
operations into smaller tasks: At this stage, operations unit workers were
grouped according to their occupational tasks, and then, the tasks of each
occupation was analyzed.
Table 1: Determination of the degree of risk through the
toxic or harmful effects of chemicals
|
Risk degree |
Description of the effects of chemicals in the division
of chemical hazards |
Example |
|
1 |
Substances that do not have any known health effects and
have not been classified as toxic or harmful Substances that have been categorized as group A5 (not
suspected as a human carcinogen) by the ACGIH |
Sodium
chloride, calcium carbonate |
|
2 |
Materials that have reversible effects on the eyes,
skin, and mucous membranes, but their effects are not severe enough to cause
serious damage to human beings Substances that the ACGIH has categorized as group A4
(not classifiable as a human carcinogen) |
Acetone,
butane, acetic acid |
|
3 |
Substances that are possibly carcinogenic or mutagenic
to humans or animals, but there is not enough information about
cancer-causing substances that the ACGIH has categorized as group A3 (confirmed animal carcinogen with unknown relevance to
humans). |
Toluene,
xylene, ammonia |
|
4 |
Substances that may be carcinogenic, mutagenic, and
teratogenic according to studies carried out on animals The number of these substance are more than the previous
category Substances that the ACGIH has categorized as group A2 (suspected human carcinogen). |
Formaldehyde,
cadmium, methylene chloride |
|
5 |
Substances known for their carcinogenic, mutagenic, and
teratogenic effects substances that have been categorized by the ACGIH as
group A1 (confirmed human carcinogen) |
Benzene, lead,
arsenic |
ACGIH: American Conference of
Governmental Industrial Hygienists
3.
Identification of chemicals: At
this stage, all chemicals (including general, intermediates, products, and
by-products) that were produced or consumed during the process were identified.
All materials in the form of solid, liquid, gas, vapor, mist and fume dust were
examined. In this study, basic instructions, process flow diagrams, and process and instrument diagram (P&ID)
were used to identify chemicals.
4.
Determination of the degree of
risk: Tables 1 (determination of chemical safety) and 2 were used to determine
the toxicity of materials.
Table 2: Determination of the degree of risk using the acute
toxicity of chemicals
|
LD50 absorbed orally (mg/kg
body weight of rats) |
LD50 absorbed through the skin
(mg/kg body weight of rats) |
LD50 absorbed through inhalation in rats (mg/l gases and vapors in 4
hours) |
LD50 absorbed through inhalation in rats (mg/l, aerosols and
particulate matter in 4 hours) |
Degree of risk |
|
LD50 > 2000 |
LD50 > 2000 |
LC50 > 20 |
LC50 > 5 |
2 |
|
200 < LD50 < 2000 |
400 < LD50 < 2000 |
2 < LC50 < 20 |
1 < LC50 < 5 |
3 |
|
25 < LD50 < 200 |
50 < LD50 < 400 |
0.5 < LC50 < 2 |
0.25 < LC50 < 1 |
4 |
|
LD50 < 25 |
LD50 < 50 |
LC50 < 0.5 |
LC50 < 0.25 |
5 |
5.
Determination
of the degree of exposure (ER) with the exposure index (EI:( In this study, considering that air monitoring results
(measurement results of exposure) were not available, the degree of exposure
was calculated with theEI according to the following formula:
where n is the number of used exposure factors.
The EI was obtained based on a numerical scale (1 to 5; 1
= very low, 3 = medium, and 5 = very high) using table 3.
Table 3: Determination of exposure index
|
5 |
4 |
3 |
2 |
1 |
Exposure index |
Exposure factor |
|
More than 100 mmHg, Powder, dry
and fine particles Less than 10 micrometers |
10-100
mmHg Fine and dry materials Between
10 and 100 micrometers |
0.1-10
mmHg Fine
and dry particles More than 100 micrometer |
0.1-1 mmHg Fine and dry particles |
less than 0.1 mmHg Coarse particles and wet
material |
Vapor pressure or particle size in terms of
aerodynamic diameter |
|
|
2 < |
1-2 |
0.5-0.99 |
0.1-0.49 |
<
0.1 |
Ratio of olfactory threshold to permissible exposure
limit |
|
|
Without any control (very high
level of dust) |
Inadequate control (much dust) |
Adequate control and
maintenance (dust average) |
Adequate control with regular
maintenance |
Adequate control with regular maintenance |
Control measures |
|
|
- High usage rate - Workers have not been trained to work with
chemicals - More than 1000 kilograms or liters |
High usage rate - Workers have been trained to work with chemicals - 10-1000 kilograms or liter |
Average amount of use - Workers have been trained in the transportation of
chemicals - 1-100
kilograms or liters |
low amount of use - 1-10 kilograms or liters |
Negligible amount of use -
Less than 1 kilogram or liter |
Amount of material used per week |
|
|
32-42 hours |
32-42
hours |
16-24
hours |
8-16 hours |
Less than 8 hours |
Working time per week |
|
In the above
table, when the chemical is in liquid form at room temperature, the risk of
exposure to it depends on its vapor pressure, which can be obtained from the
material safety data sheets (MSDS).
In the case
of one solid chemical substance, the risk of respiratory exposure depends on
the size of the solid particles. The particle size can be obtained by
calculating the aerodynamic diameter of particles using the following equation:
where Dp is the particle diameter, Da is the
aerodynamic diameter and s.g the density.
Moreover, the level of exposure to a chemical substance in the fourth and
fifth rows of the above tables depends on the amount and duration of exposure. In this study, 1 week work period (usually
40 hours) is considered as the basis for determining the exposure factor.
1.
Risk assessment: At this stage,
according to the hazard rate (HR) and exposure rate (ER) of chemicals, the risk
was obtained using the following equation. It should be noted that in this study,
when the level of calculated risk was not a whole number, it was rounded up to
the nearest whole number.
2.
Rating of risk: The risk of
occupational exposure to chemicals in each task was ranked using the risk level
and the ranking of risks were as follows:
·
Risk level 1: Small–negligible
·
Risk level 2: Low
·
Risk level 3: Medium
·
Risk level 4: High
·
Risk level 5: Very high
The
following matrix used to determine the level and rank of risk (Table 4).
Table 4: Matrix
ranking risk
|
ER HR |
1 |
2 |
3 |
4 |
5 |
|
1 |
1 |
1.4 |
1.7 |
2 |
2.2 |
|
2 |
1.4 |
2 |
2.4 |
2.8 |
3.2 |
|
3 |
1.7 |
2.4 |
3 |
3.5 |
3.9 |
|
4 |
2 |
2.8 |
3.5 |
4 |
4.5 |
|
5 |
2.3 |
3.2 |
3.9 |
4.5 |
5 |
|
Guideline |
|
|
Small-negligible |
|
|
Low |
|
|
Medium |
|
|
High |
|
|
Very high |
|
Results
This study was performed on 95 employees working in the operation unit of a petrochemical
company. In this study, the mean and standard deviation of age of participants
was 30.28 ± 7.87. The mean and standard deviation of their work experience was
5.98 ± 5.66. Moreover, 25.3% of the participants were
single and 74.7% married. As can be seen in table 7, there were significant
differences between the mean age and job tenure of individuals at low and high
risk.
Table 5 is presents the ranking of risk in Job tasks of the PX (P-xylene) process
in unit 400. As can be seen in table 5, the highest risk was related to work
with benzene with risk level 4. Other tasks were exposed to chemicals with risk
level 3.
Table 5: Ranking of
risk in Job tasks of PX (P-xylene) process
in unit 400
|
Risk level |
Exposure rate |
Hazard rate |
Chemical |
Task |
Row |
|
3 |
3.1 |
3 |
Xylene |
Washing of
unit equipment |
1 |
|
3 |
2.2 |
3 |
Xylene |
Sampling of
products as an example |
2 |
|
3 |
2.2 |
3 |
Toluene |
||
|
4 |
2.2 |
5 |
Benzene |
||
|
3 |
2.2 |
3 |
Xylene |
Routine
replacement of pumps for lower equipment depreciation |
3 |
|
3 |
2.2 |
3 |
Xylene |
Opening and
shutting of valves |
4 |
|
3 |
2.2 |
3 |
CO |
Inspection of
the furnace in service |
5 |
|
3 |
2.2 |
3 |
H2S |
||
|
4 |
2.2 |
5 |
Benzene |
Substitution
of KLAY DRAM |
6 |
|
4 |
4.4 |
3 |
Xylene |
Table
6 presents the risk ranking in Job tasks of the PX process in unit 700-800. As listed in table 6, the tasks include
replacing of ammonia cylinders, Inspection of the state of the PDEB (Para
diethylbenzene), cleaning of equipment, inspection and replacement of nitrogen
cylinders in the absorption tower (tower 8801 and related reflux drum),
inspection of the operation of compressors turbine, sampling of products as an
example, inspection of fans, routine replacement of pumps for lower equipment
depreciation, purification of PDEB solvent in T-7005 towers, and inspection of
the state of the furnace in service.
In this unit, all tasks had a level 3 risk, except the
inspection of fans and replacement of pumps that had a level 2 risk.
Table 7 presents the tasks of the PX process in unit 950; the lowest risk
level was 2 and the highest was 3. The amount of risk level is illustrated in
figure 1. In this study, 72%, 19%, and 9% of risk was at a medium, low, and
high level.
Table
6: Risk ranking in Job tasks of PX (P-xylene)
process in unit 700-800
|
Risk level |
Exposure rate |
Hazard rate |
Chemical |
Task |
Row |
|
3 |
3.4 |
3 |
Ammonia |
Replacement
of ammonia cylinders in unit 800 |
1 |
|
3 |
3 |
3 |
Para diethylbenzene |
Inspection of the state of the PDEB (Para diethylbenzene) |
2 |
|
3 |
2.6 |
3 |
Xylene |
Cleaning
of equipment |
3 |
|
2 |
1.7 |
1 |
Nitrogen |
Inspection
and replacement of nitrogen cylinders in the absorption tower |
4 |
|
3 |
2.1 |
3 |
H2S |
Inspection of Tower 8801 and related reflux drum |
5 |
|
3 |
2.1 |
3 |
H2S |
Inspection
of the operation of the turbine compressors |
6 |
|
3 |
2.5 |
3 |
H2S |
Sampling
of products as an example |
7 |
|
2 |
2.1 |
1 |
CH4 |
Inspection
of fans |
8 |
|
2 |
2.6 |
1 |
C1-C4 |
Routine
replacement of pumps for lower equipment depreciation |
9 |
|
3 |
2.6 |
3 |
CO |
||
|
3 |
3 |
3 |
Para diethylbenzene |
Purification
of PDEB solvent in T-7005 towers |
10 |
|
3 |
2.5 |
3 |
H2S |
Inspection
of the state of the furnace in service |
11 |
Table
7: Risk ranking in tasks of the PX process in unit 950
|
Risk level |
Exposure rate |
Hazard rate |
Chemical |
Task |
Row |
|
3 |
2.1 |
3 |
H2S |
Deaeration
of pumps |
1 |
|
2 |
2.1 |
1 |
CH4 |
||
|
3 |
3.4 |
2 |
Chemical 1044 |
Cleaning
of equipment |
2 |
|
3 |
2.5 |
3 |
H2S |
Inspection
of the operation of the turbine compressors |
3 |
|
2 |
2.2 |
1 |
C1-C5 |
Sampling
of products as an example |
4 |
|
2 |
1.5 |
2 |
Grace |
Inspection
of fans |
5 |
|
3 |
2.4 |
2 |
Oil |
Routine replacement of pumps for lower
equipment depreciation |
6 |
|
3 |
2.2 |
3 |
H2S |
Inspection
of the state of the furnace in service |
7 |
|
3 |
2.2 |
3 |
CO |
Discussion
In this study, workers were exposed to 19 chemicals during the performance
of their duties. Among these materials, benzene and xylene had the highest
risk. These two chemicals were present
in the tasks of sampling of products as an example, cleaning of the unit
equipment, replacement of pumps, opening and shutting of valves, and inspection
of drum reflux. This study showed that Xylene have higher risk level in job task
of PLAY DRAM replacement compared to other tasks. Das it have priority to reduce
through modification of task and use of appropriate protective equipment.
Benzene with is a high-risk (number 5) chemical and has toxic effects.
However, given the low exposure levels (2), a control measure was established
based on the reduction of exposure to this material to reduce the degree of
exposure to rating 1.
In the study by Malakooti et al., no significant relationship was found
between risk of chemicals in laboratory workers and marital status (13).
Nevertheless, in the study by Ghods et al. conducted to investigate the
epidemiology of occupational accidents in Semnan, it was found that 63% of accidents
occur among married employees. As mentioned above, the results of this study
showed a significant relationship between risk and marital status (P <
0.015) (14).
The results showed that experience and age affected the risk level. Several studies have reported
the prevalence of accidents in individuals with low experience (15-18). Thus,
we can conclude that occupational history and experience is effective in
reducing exposure to chemicals. In this study, no relationship was observed
between the level of education and risk level. This was also observed in the
study by Kingdom et al. on risk assessment of chemicals in the laboratory (13).
This study had
some limitations, including that some of the chemicals that existed in the
investigated industry were not listed on the MSDS, so it was not possible to
assess them. Another limitation of this study was that micromaterials and
nanomaterials that are not identifiable through the available methods and tools
may be present in companies. Since there is no regular program in the country
to assess and prioritize chemicals in industries, the use of this method is
proposed as a systematic assessment method for evaluating chemicals and
prioritizing strategies to control chemicals.
Conclusion
It can be concluded from this study that 81% of chemicals used in the
studied industry were rated as moderate and high risk. In order to control the
identified risks, programs and control measures are recommended based on the
hierarchy of elimination, substitution, engineering control, administrative
control, and use of personal protective equipment.
Acknowledgments
The authors are grateful to the faculty members of the Department of
Occupational Health and all managers and staff of the studied petrochemical
plant for their cooperation in this project.
Conflict of interests: None declared.
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* Corresponding author: Ali Firoozi chahak, Dept. of Occupational Health, Faculty
of Health, Gonabad University of Medical Sciences, Gonabad, Iran.
Email: ali_firoozi66@yahoo.com