الفهرس 
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Abstract
Natural gas is a hydrocarbon mixture consisting primarily of methane, but commonly includes varying amounts of other higher alkanes and even a lesser percentage of carbon dioxide, nitrogen, and hydrogen sulfide. It is an energy source often used for heating, cooking, and electricity generation. Emissions can occur during extraction, production, processing, flaring, transportation and distribution of oil and natural gas. Those emissions can be vented to the atmosphere (intentionally or unintentionally) and impact air quality. Air pollutant exposures are associated with increased risks of respiratory diseases. SO2 and NOx are known triggers for asthma attacks and increase risk for lung and heart disease. Results of effects of natural gas processing emissions on the lung health are equivocal.
Aim of the work
To study prevalence of respiratory symptoms, lung function impairment and CXR changes in workers exposed to natural gas processing emissions and to correlate findings with environmental measurements.
Subjects and methods
Subjects
This is a cross sectional study, where 307 subjects were selected from a natural gas company. All available exposed workers in the processing plant situated in Dakahlia governorate were included in the study (152 worker) and a comparable number of administrative employees (155 subject) who were not exposed to any noxious gases were also included and selected randomly.
Methods
The following tools were employed for data collection. These included:-
vii. Occupational history questionnaire.
viii. Medical Research Council Questionnaire on respiratory symptoms and smoking habit.
ix. Anthropometric measurements.
x. Forced expiratory spirometry.
xi. Standard postero-anterior CXR imaging.
xii. Three air sampling trains, each of which consisted of a personal suction pump and two bubblers for assessment of work place environmental levels of SO2, NO2 and H2S.
Results
1- The exposed workers in the studied natural gas processing plant were distributed nearly equally in the 10 zones of the plant.
2- The environmental measurements of natural gas processing emissions of SO2, NO2 and H2S were far below the recommended TLVS.
3- Both exposed workers and unexposed subjects were nearly similar in age and smoking habit.
4- The proportions of exposed workers complaining of cough in winter first thing in the morning, cough either by day or night and cough for three months or more during the year (19.1%, 19.1% and 15.8% respectively) were significantly higher than those in unexposed workers (3.9%, 3.2% and 1.3% respectively).
5- The frequency of exposed workers complaining of phlegm production first thing in the morning and phlegm production in most days for at least 3 months per year (21.7% and 17.8% respectively) were significantly higher than those in unexposed workers (5.2% and 1.3% respectively).
6- The prevalence of exposed workers complaining of wheeze and any chest disease preventing normal activity for more than a week during the past 3 years (6.6% and 20.4% respectively) were significantly higher than those in unexposed workers (0.0%, 5.2% respectively).
7- The proportions of exposed workers complaining of past history of cardiac problems, chronic bronchitis and pneumonia (6.6%, 15.1% and 24.3% respectively) were significantly higher than those in unexposed workers (0.6%, 0.6% and 5.8% respectively).
8- The frequency of exposed workers received treatment for bronchial asthma and allergic rhinitis (4.6% and 13.2% respectively) were significantly higher than those in unexposed workers (3.9% and 4.5% respectively).
9- Correlation / regression relationship between lung function indices (LFI) and exposure, after allowing for height, weight, age and smoking habit, found that the mean values of FEV1, PEFR, FEF75, FEF50, FEF25 and MVV in the exposed workers were significantly lower than those of unexposed subjects.
10- Correlation / regression relationship between lung function indices (LFI) and duration of exposure, after allowing for height, weight, age and smoking habit, found that increase duration of exposure to natural gas was significantly associated with decrease in FEV1, PEFR, FEF50, FEF25 and MVV.
11- Regression relationship revealed that increase concentration of SO2 and NO2 was significantly associated with decrease in FEV1, PEFR, FEF50, FEF25 and MVV.
12- Regression relationship revealed that increase concentration of H2S was significantly associated with decrease in FEV1, PEFR, FEF75, FEF50, FEF25 and MVV.
13- Increase concentration of SO2, NO2 and H2S was significantly associated with increased bronchovascular markings in CXR.
Conclusion
Chronic exposure to natural gas processing emissions is significantly associated with increased respiratory symptoms and obstructive impairment of air ways.
Recommendations
1- BMRC questionnaire and lung function assessment of airways caliber should be included in periodic medical examination.
2- Current TLVs for emission contaminants must be reconsidered.
3- Further researches should be conducted to confirm findings from the present study.