Assessment of health risks of exposure to hazardous chemicals by semi-quantitative method in a gas refinery complex
Samimi K, MSc1, Asiliyan H, PhD2*, Khasedar K, MSc3, Khavanin A, PhD2
1- MSc of Occupational Health Engineering, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran.2- Associate Prof, Dept. of Occupational Health Engineering, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran. 3- Head of Industrial Health Unit, Gas Refinery, Birjand, Iran.
Abstract Received: December 2016, Accepted: February 2017
Background: Gas refining is a process in which workers are exposed to different chemicals. This study aimed to assess the health risks caused by exposure to these substances in order to determine hazardous jobs and to present controlling methods. Materials and Methods: This cross-sectional study was performed on the workers at gas refinery in 2015. The sample included all the staff in operational parts and the selection was by census. To determine the risk of exposure to chemical pollutants, the method proposed by the Department of Occupational Safety and Health of Malaysia was used. Following this procedure, first the materials and processes were identified. Afterwards, risk and exposure rates were calculated. Using these two rates and risk rate formulas for individual chemicals, the exposure was calculated. Results: The results showed that employees were exposed to 103 different types of chemicals that collectively were causing 162 types of exposure in different jobs. Of the total exposures, 5 percent were evaluated as “inconsiderable risk rate”, 51 percent as low, 30 percent average, 13 percent high, and 1.2 percent as “very high risk rate”. Conclusions: The highest risk rate of exposure to chemicals in the refinery was related to benzene in stabilizer and topping area shift works (RR = 5) as well as the shift works in feller area and evaporation pools with risk rate of 5, ranking their risk as very high, indicating that corrective actions should start on this hazardous and carcinogenic chemical as soon as possible. |
Keywords: Risk Assessment, Hazardous Chemicals, Occupational Exposure
Introduction
Chemical pollutants in the workplace include gases, vapors, and solid and liquid particles. Excessive exposure to these substances in the workplace can cause poisoning and various diseases (1, 2). In the last fifty years, the number of factories producing chemicals has risen sharply, and new products are introduced into market each year. In 1942, the number of chemicals identified was about 600,000. In 1947, the number reached some 4 million and is currently 78 million (3, 4). Also, there are a lot of chemicals that were previously considered as safe or low-risk for humans but were later regarded as carcinogens such as asbestos or thalidomide which causes genital disorder (5). Hazard refers to situations that have the potential of causing harm to people. Risk refers to the possibility of whether a hazard can harm a person or group at a certain point of time. Both hazards and risks can be expressed in words or numbers or any other meaningful way. What is obvious, at any rate, is that if there is no an exposure to hazards, there will not be any risk (6).
A main pillar of Health, Safety and Environmental (HSE) Management System is risk assessment where the goal is to identify, evaluate and control risk factors that influence the health and safety of staff in industry (7). In Occupational Health and Safety Assessment Series (OHSAS) 18001, risk assessment is defined as an evaluation process of risks caused by hazards in the workplace by considering controlling measures and deciding about their acceptability (8).
The purpose of chemical risk assessment is to identify potential risks of chemical substances, to assess workers’ exposure to hazardous chemical substances, and to determine the risk of unintended deleterious effects on people as caused by contact with hazardous chemical substances (9, 10).
Without a way that can help to classify potential risks, costs and resources may be used in controlling risks that are of less priority at the expense of high-risk jobs (11). It is additionally required to evaluate health risks for proper decisions to be made concerning control and protection measures against complications of chemicals (12, 13). In other words, chemical health risk assessment can make it possible to do a comprehensive assessment of employees’ exposure to hazardous health factors and make decisions about control measures and provision of care and education for the staff (14).
The semi-quantitative method of risk assessment of hazardous chemicals was first developed in 1994 by the Australian Commission on Safety and Quality in Health Care and was published by the Australian Government Publishing Service (13).
In 2000, a more complete version of this method was proposed by the Department of Occupational Safety and Health of the Malaysian Ministry of Human Resources (11).
Singapore's Occupational Safety and Health Division then introduced it as a method of risk assessment of chemicals in this country (9).
Based on this method, Hunadia Husin and Abu Bakr Muhammad et al. (2010) evaluated the health risks of hazardous materials in the chemical and biochemical engineering laboratories (15).
Also, in a case study in the Iranian National Petrochemical Industry, Jahangiri and Parsarad evaluated the health risks caused by the chemicals in the industry through a semi-quantitative method (14).
In another study, Golbabaei et al. assessed the health risks of exposure to chemical contaminants with an emphasis on the risk of leukemia in a petrochemical industry (16).
Another study was carried out by Jahangiri et al. in order to assess the health risks of exposure to chemicals in the polyurethane foam manufacturing industry by the mentioned method (17)
Materials and Methods
This cross-sectional study was performed on the workers at gas refinery in 2015. The sample included all the staff in operational parts selected by census (Table 1).
Table 1: The number of employees in working unit
Working unit |
Number of employees |
Water and steam |
21 |
Gas treatment |
5 |
Auxiliary operation unit |
18 |
Sales operation |
41 |
Maintenance and repairs |
160 |
Power house |
17 |
laboratory |
16 |
Consolidation and rectification |
8 |
General services unit |
98 |
The method proposed by the Malaysian Department of Occupational Safety and Health was used to determine harmful chemical exposure risks, and procedure that was followed in this study is described below:
(A) Formation of a work group
According to this method, first a work group was formed whose members included the employer’s representative (project supervisor) – occupational health specialist – and the head of the unit or his/her representative (11).
(B) Decomposition of the process into smaller tasks
Different industry departments and existing processes in each department and different jobs under each process were determined. Then the exact job description of the staff was extracted for which interviews were made, and documentation of organizational tasks were collected.
(C) Chemical identification
In the next step, all chemicals to which the working personnel might be exposed such as raw materials, intermediate materials, and main products and accessories were identified by observing the processes and checking process maps such as Process Flow Diagram (PFD) and Piping and Instrumentation Design (PID) and by examining chemical reactions and inventories lists. Afterwards, safety and health information of each of the substances was extracted using Material Safety Data Sheets (MSDS), container tags, and the information provided on the manufacturer’s website was extracted. Based on this information, it was estimated whether and to what extent the materials could be hazardous.
(D) Hazard rate determination
According to the method recommended by the Malaysian Department of Occupational Health (11), the hazard rate of the identified chemicals can be obtained by lethal dose (LD50), lethal concentration (LC50), or toxic effects of chemicals. This information can be extracted from chemical health and MSDS and warning labels on chemical packages. After determining the risk numbers for each substance based on the above parameters, the largest number is selected as the hazard rate.
(E) Exposure rate
Exposure rate to chemicals can be calculated in two ways: (a) determination of actual exposure level for substances whose sampling and monitoring results were available. The exposure rate of 76 substances in different jobs was calculated in this way. For this purpose, a private company licensed by the Iranian Ministry of Health was called for to measure and estimate the availability level of some major chemicals, which were considered to be likely present in staff’s breathing during the identification stage, (b) determination of exposure indices for substances for which the monitoring results were not available. The exposure rate of 76 substances in different jobs was calculated in this way. To determine staff exposure indices to a certain chemical, five criteria are involved each having five modes (9).
First criterion: steam pressure (in the case of gases and vapors) and particle size (in the case of dust)
Second criterion: the olfactory threshold contact limit (OT/PEL)
Third criterion: inventory control measures
Forth criterion: daily consumption of chemicals in kilograms or liters per week
Fifth criterion: duration of working with chemicals in terms of hours per week
(F) Determination of risk level
After determining hazard rate (HR) and exposure rate (ER), the risk rate (RR) for individual chemicals in all jobs was calculated according to the following formula or matrix table.
(G) Risk rating
The risk level of each chemical with exposure was extracted. Moreover, the chemical’s risk rate was determined according to table 2. This rating is in fact a basis to prioritize controlling measures for reducing exposures and chemical effects in the refinery. These actions can include technical and engineering measures such as process change or removal and replacement of dangerous substances, installation and upgrading ventilation systems as well as management measures like reduced exposure time through new rest-work shifts, rotational shifts, and finally, application of personal protective equipment.
Table 2: Risk rating
Rating |
Risk rate |
Inconsiderable |
0-1.7 |
Low |
1.7-2.8 |
Average |
2.8-3.5 |
High |
3.5-4.5 |
Very High |
4.5-5 |
(H) Implementation of a corrective action plan
Controlling and corrective measures were defined after determining the risk rate for chemicals exposure to which was estimated as high and very high.
(I) Documentation of evaluation
All evaluations were recorded in the forms numbered 1, 2a, 2b and 3. Thereafter, they were stored on the refinery HSE unit computer.
The points that should be considered in this method include:
Results
In this study, all refinery units were exactly examined. A total of 21 working processes including 58 job titles with 393 employees were identified which were exposed to 162 chemicals. Number 1, 2, and 3 forms were completed for this category of processes and tasks.
Five percent of workers’ exposure to chemicals is of an “inconsiderable rate”, while 57% is in “low rate”, 30% in “average”, 13% in “high”, and 1.2 of a “very high” rate (Figure 1).