Diesel engines are very accessible technology for many industries and also widely used in underground mining because of its efficiency, versatility, reliability, and durability (Burgasky, 2012). Besides advantages, diesel engines have disadvantages due to gas and substantial emission also known as diesel particulate matter (DPM). Diesel engines produce a different discharge in solid and gas phase (Talla, 2012). Carbon monoxide (lower than gasoline engines), nitrogen dioxide and volatile organic compound like benzene and formaldehyde are in the gas phase while elemental and organic carbon, ash, sulfate, and metals are in the solid phase. Polycyclic aromatic hydrocarbons and nitroarenes distribute over the gas and the particle phase. DPM concentration is six to ten times higher than the petrol engine (Resitoglu, 2015).
Pollutant emissions have a rate of less than 1 % in the diesel exhaust gas (Resitoglu, 2015). Nitrogen Oxide (NOx) has the most substantial proportion of diesel pollutant emissions with a balance of more than 50 % (Resitoglu, 2015). After NOx emissions, PM has the second largest percentage of pollutant emissions. Because diesel engines are lean combustion engines, the concentration of CO and HC is minimal (Resitoglu, 2014). DPM has more attention since declaring as a group 2A category "probably carcinogenic to humans" by WHO on 1988. Twenty-four years later, it has been becoming to group 1 "carcinogenic to human" (WHO, 2012).
Nowadays there is no regulation or standard on DPM in Indonesia mining industry. Diesel emission regulations from the government of Indonesia only are arranged to protect underground mine worker from diesel emission for CO and NOx gas (Kepmen PE No 555.MPe/1995 article 387.5). There are 15 underground coal mines and seven underground non-coal mines operating today in Indonesia. Underground coal mining does not use diesel engines in their operation on the mine tunnel while on the non-coal mining, almost all drilling use diesel engines in their process. Because of the hazard from DPM as a carcinogenic material to human, it is essential to understand DPM risk in Indonesia underground mining industry.
To have an understanding about DPM issues all over the world, this research was performed by reviewing paper from ten journals, two proceedings, one textbook, four reports, and also looked at one legislation, one guidance and one standard published on DPM topic.
To analyze DPM risk emitted by diesel engines, it was conducted by sending a questionnaire to six underground mining company all around Indonesia.
Based on the review of relevant material on several kinds of literature and the survey, the DPM issues will be described below.
Diesel particulate matter (DPM) properties
Diesel particulate matter is a submicrometer aerosol emitted by diesel engines. DPM is considered to be a product of incomplete combustion of fuel and lubricant hydrocarbons. The chemical, physical, and toxicological properties of DPM depend on many parameters. The parameters are engine design, engine operating conditions, fuel, and lubricating oil properties, exhaust after treatment, environmental conditions, also engine age (Burgasky, 2012).
Mined materials by drilling, blasting, grinding, crushing, handling, and transportation operations are the primary source of respirable dust containing coarse particles with an aerodynamic diameter of roughly one μm and ten μm (Burgasky, 2012). Diesel engines are the primary source of submicrometer aerosols (aerosols composed of particles that are less than one μm in diameter) in underground mines that using diesel-powered equipment (Cantrell et al, 1991). Underground miners are the highest suspect among workers in all occupations to become exposure by DPM (Cohen et al, 2002 & Pronk et al, 2009). The DPM exposure rates of underground miners are higher than railroad workers and truck drivers (Cohen et al, 2002).
DPM produced by diesel engine combustion have a variance on size diameter, but generally on submicron-diameter. There are three mode on DPM emitted by the diesel engine : nucleation mode, accumulation mode and coarse mode (Whitby&Cantrell, 1976). To have a better understanding of DPM diameter, it can be seen in Figure 1. Based on the illustration, it shows that the DPM position has a significant number below 0.01 μm. Because of its size diameter, DPM can enter the blood vessel through tissue organ in human pulmonary (Glyn, 2012).
DPM health effect
DPM can result in acute and chronic health effects depending on the dosage and length of exposure (Evan, 2015). Dangerous effects can cause severe irritation, neurophysiological symptoms, respiratory symptom, immunologic effect the exacerbation of allergenic response to known allergens and asthma-like symptom (EPA, 2002). Chronic health effects are divided into non-cancer and carcinogenic. Noncancer outcome based on human research is inadequate to judge health effects on human. However, based on the research study to an animal, DPM shows a spectrum of dose-dependent inflammation and histopathological changes in the lung in several animal species including rats, mice, hamsters, and monkeys (EPA, 2002).
Nowadays, based on many research studies, there is possible correlation DPM exposure and lung cancer as a chronic effect (Villeneuve, 2011 & WHO, 2012). The research study by Vermeulen et all in 2014 analyzed that three different epidemiology studies showed that at least 6% death case per year was caused by DPM exposure. Because of its dangerous, DPM was declared as a group 1 category "carcinogenic to human" by WHO on 2012.
Several countries published guidance to limit DPM exposure in the working environment to protect the worker from DPM health hazard outcome (Table 1).
Diesel engine emission standard was also published both in Europe and America. Today, Euro Standard implemented 0.01 g/kWh for particulate on Euro 6 category for Bus and truck while in America, EPA Tier 4f reduced the number of particulate to 0.01 g/hp-from 0.4 g/hp-hr on tier 1 in 1996.
The current DPM exposure standards were not establish as health-based standards, but feasibility standards. Lack of defined universal dose –responses relationship for complex aerosols prevented creating health-based exposure level (Burgasky, 2014). As a reference, the excess lifetime risk (XLTR) of exposure to 0.8 μg/m (ambient) was estimated to be 21 additional lung cancer deaths per 10.000 individuals as compared to an unexposed population (Vermeulen et al. 2014).
Understanding diesel emission on everyday performances in underground mining is important to understand how many DPM emitted from diesel engines operation. DPM emission rate based on daily performance could be understood based on the research report by Rubelli and Gangal (2003) in Canada. The data in Table 2 was modified to have an emission rate summarize to become two categories, high duty vehicle (HDV) and low duty vehicle (LDV).
The best controlling technics to reduce hazard came from the source. In the last 30 year, diesel engines modification made rapid progress to minimize particulate and nitrogen oxide emission (Fiebig, 2014). Several technologies were invented to control diesel engine emission besides combustion efficiency of the engine and fuel selection. There was a view of an emission control device that could be possible to reduce DPM emission. The device technology was the particulate filter, catalytic converter, scrubber, acoustic agglomeration also cyclone (Gov of Western Australia, 2013). The particulate filter and catalytic converter could reduce by nearly 100% of a particle (Fiebig, 2014).
Diesel engine operation in several underground mine in Indonesia
All of 7 non-coal mining company were targeted as a respondent for the research. There were five mining companies sending feedback to participating as a respondent. The result of the diesel engine number and emission rate estimated was shown in Table 3 below.
|Respondent||Number of diesel engine||DPM Emission Rate (estimated) (g/hr)|
The DPM emission rate estimation was calculated from the number of the diesel engine in the underground mining company with diesel emission rate in Table 2.
The highest diesel engine population came from respondent number 1 with 717 HDV and 308 LDV and was assumed 16.627 g/hr DPM emitted to the mine tunnel environment. The lowest diesel engine population came from respondent number 5 with 0 diesel engine operation in the tunnel and also with 0 emission rate. Based on the DPM emission rate estimation, it meant that the higher number of diesel engines service related to emissions rate was increasing. Because of the carcinogenic effect of DPM to the human, Indonesian underground mine workers especially for company respondents 1 to 4 were in the high-risk condition as a lung cancer suspect. The government of Indonesia should concern to monitor DPM emission in the mining environment, because of many evidence today from all over the world leads DPM has a carcinogenic effect on the human lung.
This research was only for the preliminary study to understand the condition of underground mining operation compared to the DPM emission risk in Indonesia. It should be following with another research to assess the correct emission rate in several underground mines with more general parameter including; diesel engine type, fuel, and lubricating oil, exhaust after treatment also working condition to support the government of Indonesia with more reliable data to publish regulation on DPM topic.