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|Year : 2009
: 11 | Issue : 43 | Page
|Noise characteristics of grass-trimming machine engines and their effect on operators
Zulquernain Mallick1, Irfan Anjum Badruddin2, MT Khaleed Hussain3, NJ Salman Ahmed3, Jeevan Kanesan4
1 Department of Mechanical Engineering, Faculty of Engineering and Technology, Jamia Millia Islamia, New Delhi, India
2 Department of Mechanical Engineering, University of Malaya, Kuala Lumpur, 50603, Malaysia
3 School of Mechanical Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Malaysia
4 Department of Electrical Engineering, University of Malaya, Kuala Lumpur, 50603, Malaysia
Click here for correspondence address
Over the last few years, interaction of humans with noisy power-driven agricultural tools and its possible adverse after effects have been realized. Grass-trimmer engine is the primary source of noise and the use of motorized cutter, spinning at high speed, is the secondary source of noise to which operators are exposed. In the present study, investigation was carried out to determine the effect of two types of grass-trimming machine engines (SUM 328SE and BG 328) noise on the operators in real working environment. It was found that BG-328 and SUM-328SE produced high levels of noise, of the order of 100 and 105 dB(A), respectively, to which operators are exposed while working. It was also observed that situation aggravates when a number of operators simultaneously operate resulting in still higher levels of noise. Operators should be separated 15 meters from each other in order to avoid the combined level of noise exposure while working with these machines. It was found that SPL, of the grass-trimmer machine engines (BG-328 and SUM-328SE), were higher than the limit of noise recommended by ISO, NIOSH, and OSHA for an 8-hour workday. Such a high level of noise exposure may cause physiological and psychological problems to the operators in long run.
Keywords: Grass-trimming machine, human health, noise, sound pressure levels
|How to cite this article:|
Mallick Z, Badruddin IA, Khaleed Hussain M T, Salman Ahmed N J, Kanesan J. Noise characteristics of grass-trimming machine engines and their effect on operators. Noise Health 2009;11:98-102
|How to cite this URL:|
Mallick Z, Badruddin IA, Khaleed Hussain M T, Salman Ahmed N J, Kanesan J. Noise characteristics of grass-trimming machine engines and their effect on operators. Noise Health [serial online] 2009 [cited 2020 May 30];11:98-102. Available from: http://www.noiseandhealth.org/text.asp?2009/11/43/98/50694
| Introduction|| |
Grass trimming is one of the large-scale male-dominated operations carried out in almost all parts of Malaysia . Grass-trimming machine is an important machine used in maintenance of grass areas. The fast growth of grass in tropical areas makes the grass-trimming operation compulsory. The petrol-engine-driven grass trimmers are widely used in Malaysia for cutting long grass along the roadside and general agricultural land. The workers involved in these activities are generally contract workers with no or little awareness of the effect of noise on health. Highways authority maintains the sideways of the road by getting the grass cut by these contract workers. This is very large industry with a workforce of more than 20,000 workers. Safe and comfortable working environment is one of the factors required for the productivity of operators engaged in this work. Besides physical exertion, one of the major sources of discomfort to the workers operating a grass-trimming machine is the noise to which they are exposed. Recent studies show that noise is now recognized as a serious health problem in our modern societies. , Both auditory and nonauditory effects are prevalent among the workers/operators working in a noisy environment. The nonauditory deleterious effects of noise include: annoyance, loss of memory, and sleep disturbances. , The pace of research in agriculture sector using power tools has been rather slow in comparison to industrial sectors. Extensive research work has been carried out in agriculture field with special reference to noise exposure on operators. ,,, Zaheeruddin and Garima  developed a neuron-fuzzy model for predicting the effects of noise pollution on human work efficiency as a function of noise level, type of task, and exposure time. Much research has been carried out to determine cut-off noise levels below which operators can be exposed to about eight hours a day without increased risk of hearing loss. Levels from 66-85 dB(A) can involve physical and neurological disorders and auditory damage. The metabolic activity taking place at the moment of the arrival of noise is important; heat, heavy work, infectious disease, and other causes of heightened metabolism increase the vulnerability of the sensory organs.  Noise levels above 130 dB(A) induce turbulence in the ear and may also cause mechanical damage.  In the United States, OSHA  has specified 90 dB(A) as the maximum permissible exposure to continuous noise for 8-hour shift. The recommended exposure limit (REL) for workers engaged in the occupations such as engineering controls, administrative controls, and work practices is 85 dB(A) for 8-hour duration.  NIOSH  also recommended a ceiling limit of 115 dB(A). Exposure to noise levels greater than 115 dB(A) would not be permitted regardless of the duration of exposure. In Malaysia, the permissible limit for continuous noise exposure is 90 dB(A).  Pace of research in the field of agriculture has been rather slow in developing countries, although extensive research in this field has been carried out in developed countries. Going through the literature, it is found that either no or very little work has been done in case of grass-trimming machine noise effects on operators. This area becomes all the more important to investigate as more and more workers are hired by Malaysian Government to beautify the tourist places by way of maintaining rapid grass-growing areas. Keeping this in view, the problem was analyzed and aim of the present study was to find out the propagation characteristics of noise produced by two grass-trimming machines (BG-328 and SUM 328SE). The study also focused to find out the safe working distance for operators when two workers are working at the same time.
| Materials and Methods|| |
The string trimmer is a small machine that uses a rapidly spinning plastic line to impact and break off plants rather than cutting them. Trimmers are used for landscaping tasks such as trimming, edging, and scalping. These machines can typically cut within a radius of 15-30 cm. There are several variations found in these types of machines depending upon engine size, location, type of shaft, and handle shape. In these machines, through a long flexible driving shaft, the engine drives the cutting head containing the plastic cutting line. These engines operate the cutting head in the range of 1000-6000 rpm but full speed is typically 8000-10000 rpm, depending on engine power, number of cutting lines, and type and depth of grass. Noise-producing machines have primary as well as secondary sources of noise. In most cases, the primary source of noise is of interest for the analyst whereas contribution of secondary source is negligible. In the present case, grass-trimming machine engine is primary source of noise whereas motorized cutter with plastic lines is secondary source of noise. When machine is operated the operators are subjected to high level of noise, the greater the speed of the cutter (in rpm) more will be the noise, causing more inconvenience to the operator [Table 1] and [Table 2]. In this study two machines BG-328 and SUM-328SE were chosen because of their widespread use in Malaysia. Specifications of the two machines are given in Appendix A-B. These machines are placed at the back of operators while trimming the grass as shown in [Figure 1].
The experiment was conducted in real working environment. It was assured that no obstruction in any form (building, active road, trees, and fences) should be there in a radius of 500 meters. The experiments were carried out in the month of June, although it is a routine operation throughout the year specifically by the side of the highways and tourist sites. Due to moderate and heavy rain throughout the year, growth of grass is uniform and requires maintenance. The environmental parameters were recorded during the experiment: mean dry bulb temperature = 24 ± 2.5 °C, relative humidity = 56 ± 5%, and wind velocity = 1.58 ± 0.35 m/s. The backpack type grass-trimming machines, BG-328 and Tanaka SUM 328SE, were used for the purpose of grass-trimming operation. The operational specifications of the grass trimmer (Appendix A-B) are important and widespread use of these trimmers made it compulsory choice for present study. BG-328 is a China-made grass trimmer while Tanaka SUM 328SE is Japan made.
The noise level was measured with the help of sound level meter which is also a data storage and display device (Brüel and Kj'r Observer Type 2260). The sound level meter was calibrated before the actual measurements. Sound propagation characteristics are determined by marking the grid points on the grass trimming place using cross staff, ranging rods, and measuring tape, at a grid spacing of 1 m × 1 m. The grass trimmer was kept at the center of the grid lines with engine operating to rotate cutting head at 5000 ± 200 rpm. This particular value of cutting head speed was chosen because it was observed during grass-trimming operation that the speed of cutting head varies depending upon the number of cutting lines, type, and depth of grass. But the average cutting head speed seldom goes below or above the value considered. The noise was measured in accordance with the guidelines furnished in ISO-1999  standards. As recommended by the ISO, microphone was placed 100 mm away from the ear of the operators so as not to disturb the sound field under investigation. Brüel and Kj'r Observer Type (2260) was used to record the equivalent sound pressure level (L eq ).
| Results and Discussion|| |
The grass trimmers under investigation typically cut grass at approximately 5000 ± 200 rpm. During the cutting operation, the speed changes due to various reasons, such as, ground condition, length and type of the grass, grass surface levels, etc. [Table 1] and [Table 2] show the sound pressure levels that were recorded at different cutting head speeds. Tachometer ONO SOKKI HT 4100 was used to measure the cutting head speed. [Table 1] and [Table 2] also indicate SPL values in the vicinity of two trimmers. It can be seen from these tables that SPL values maintained approximately constant decreasing trend by 2 dB(A) as measured at a distance of 2, 4, 6, 8, 10, and 12 meters, respectively, from the center (0,0) coordinate. The frequency analysis of SPL (L eq ) of one-third octave band observed at grid point of highest noise for each trimmer (BG-328 and SUM- 328 SE) is presented in [Figure 2]. It was observed that the main peaks of noise were at 630 Hz and 800 Hz for BG-328 (China made) trimmer and SUM-328 SE (Japan made) trimmers, respectively. It can also be concluded from the frequency curve that variation in noise level beyond 1000 Hz is rather small as compared to variation up to 1000 Hz.
The SPL contours of the two grass trimmers are presented in [Figure 3] and [Figure 4]. The SPL was maximum at the (0,0) coordinate, that is, at the place where the operator operates the machine (100 dB(A) for BG-328 and 105 dB(A) for SUM 328 SE). It is to be noted that in other noise-producing machines/equipments, operators are not so close to the point of noise-producing source. But in the present study, operators perform grass-trimming operations while machine engine is located at their back [Figure 1]. This close location of noise source and receiver makes the situation more alarming.
The SPL was 98 dB(A) around the BG-328 (China made) trimmer at the coordinates (0,1), (1,0), (-1,0), and (0,-1) and this was second highest value of SPL. Similarly, for SUM 328 SE (Japan made) trimmer second highest value of SPL at coordinates (0,1), (1,0), (-1,0), and (0, -1) was 103 dB(A). The difference in values of SPL produced by two trimmers at source by 5 dB(A) may be due to constructional feature of the engines.
Combined sound pressure level during operation
Trimming operation is carried out throughout Malaysia irrespective of the season. It is also a common practice that several operators come together while performing the grass-trimming operation. Generally the operators work in a group. This leads to high level of noise and thus the ill effects. If two sounds (of frequencies and temporal characteristics that are both random) occur at the same time, their combined SPL can be calculated from the following formula. 
Where SPL is sound pressure level expressed in dB.
In the present study it was found that, when two or more operators perform grass-trimming operation simultaneously using different grass trimmers (BG-328 and SUM 328 SE) then combined SPL to which workers are exposed are rather high as tabulated in [Table 3]. These values were obtained in real working environment when operators were working within a radius of five meters. However, the effect was negligible when operators performed trimming operation at a radius of 15 meters from each other. It can also be seen from [Table 3] that combined SPL for different combinations of trimming machines reach a value that is much higher than exposure limit of noise for 8-hour workday recommended by ISO and OSHA.
Related health effects on operators
The high noise levels, to which operators of grass trimmers are often exposed for long period of time, may lead to substantial hearing impairment and health problems. The Recommended Exposure Limit ( REL) for workers engaged in occupations such as engineering controls, administrative controls, and/or work practices is 85 dB(A) for 8-hour duration according to NIOSH.  The SPL in present study at the operators' ear is definitely higher than recommended. Situation further worsens when several operators work close to each other. The noise levels may also reach up to 110 dB(A) when three SUM-328 SE machines are operated together. Therefore, performing grass-trimming operation in a group can cause both temporary and permanent noise-induced hearing loss. In case of farm machinery, operators work for small intervals specifically during nonpeak season, whereas, the operators of grass trimmers work for long hours irrespective of the season. Therefore, considerable attention must be paid to reduce the noise level of machines, BG-328 and SUM-328 SE.
The level of noise to which these operators are exposed may have immediate as well as long-term effects. High level of noise can cause both psychological and physiological problems. Often physiological problems are associated with headaches, dizziness, nervousness, stress, annoyance, sleep disturbance, and loss of concentration. The mental arithmetic processing ability of people weakens under the impact of noise.  The most common effects of noise exposure appear in tasks such as proofreading and solving of challenging puzzles. , Direct and indirect noise impacts cause cardiovascular effects.  Noise studies have turned up alarming connections between blood pressure and noisy environments. Jansen  observed that sounds in the range of 75-90 dB(A) cause tiny blood vessels in the toes, fingers, skin, and abdominal organs to contract. Studies have indicated the adverse effects of industrial noise. These studies conclude that industrial noise exposure for 5-30 years can cause increase in blood pressure and significant increase in the risk of hypertension, compared to workers in control areas.  In the present situation, grass trimmers should be provided with earplugs or earmuffs on one hand and redesigning the grass-cutting machine should be considered on the other. In case of grass trimmers, primary noise source is engine of the trimmer and it does not have any soundproof covering. Perhaps the situation can improve in terms of noise reduction by providing properly designed soundproof covering for the engines under reference.
| Conclusions|| |
The following conclusions have been drawn from the investigation:
- The maximum SPL produced by grass trimmers BG-328 and SUM-328 SE at 5000 ± 200 rpm was found to be 100 and 105 dB(A), respectively. The difference in produced SPL may be attributed to constructional features of two trimmer engines under investigation.
- Operators are exposed to high levels of SPL (100 dB(A) for BG-328 and 105 dB(A) for SUM-328SE) if machine is operated individually and SPL still increases if operated in group, indicating the necessity of control measures to reduce noise.
- Operators should be instructed to operate not in group but individually keeping a safe radius of 15 meters or more. Thus, by placing operators at least 15 meters apart could reduce the noise level to certain extent. However, it should be noted here that the word 'safe' does not actually mean safe for the hearing because one machine alone can be so noisy that it is harmful to hearing.
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Irfan Anjum Badruddin
Department of Mechanical Engineering, University of Malaya, Kuala Lumpur, 50603
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3]
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