occupational noise in rice mills

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Occupational noise in rice mills

GV Prasanna Kumar, KN Dewangan, Amaresh Sarkar, Amrita Kumari, Banani Kar North Eastern Regional Institute of Science and Technology, Nirjuli - 791 109, Itanagar, Arunachal Pradesh, India

Correspondence Address:G V Prasanna KumarDepartment of Agricultural and Food Engineering, Indian Institute of Technology, Kharagpur - 721 302, West BengalIndia

Abstract

Background: A major occupational hazard for the workers in rice mills is the noise during the operation of various

machines. A noise survey was conducted in the workrooms of eight renowned rice mills of the north-eastern region of

India established during the period between 1980 and 1985. The rice mills were selected on the basis of the outcome

a walk-through noise survey involving several rice mills of the region. A noise survey map of each rice mill was drawn t

identify the predominant noise sources and the causes of high noise in the workrooms of the rice mill. The sound-

pressure level (SPL) in the workrooms of the rice mill varied from 78 to 92 dBA. The paddy cleaner, rubber roll sheller,

compartment separator, rice cleaner, auxiliary sieve shaker and an electric motor without enclosure were found to be

the predominant noise sources in the workrooms of the mill. The causes of high noise in the rice mills may be attribute

to the use of a long flat belt drive, crank-and-pitman mechanism, absence of an electric motor enclosure, poor machin

maintenance and inadequate acoustic design of the workroom of the rice mill. About 26% of the total labourers were

found to be exposed to higher levels of noise than 85 dBA. Subjective response indicated that about 26% of the total

labourers felt noise interferes in their work and about 49% labourers were of opinion that noise interferes with their

conversation. Context: Noise from machines in the rice mills was found to be the major occupational hazard for the ric

mill workers. The predominant noise sources need to be identified and the causes of high noise need to be studied to

undertake the appropriate measures to reduce the noise level. Aims: To identify the predominant noise sources and

their distributions in rice mills, to study the causes of high levels of noise in rice mills and to examine the response of th

workers towards noise. Settings and Design: A noise survey was conducted in eight renowned rice mills of the north-

eastern region of India. The mills were selected based on a walk-through survey conducted for the identification of rice

mills with high noise. A noise survey map of each rice mill was collected by following the guidelines of Canadian Centr

for Occupational Health and Safety (CCOHS). The distribution of high noise in rice mills was studied and the causes of

high noise were identified. The subjective response to noise in rice mills was assessed by conducting personal intervie

with all the workers of the rice mills using a structured form. Methods and Material: The guidelines of CCOHS were

followed during the noise survey. A sound level meter (SLM; Model-824) was used to record the noise level at each gri

point marked at 1 m × 1 m. SPL in weighting scale «DQ»A«DQ» and the noise spectrum were recorded at each gridpoint for 30 s and data were stored in SLM. A noise survey map of equivalent SPL was drawn for each rice mill by

drawing contour lines on the sketch of the rice mill between the points of equal SPL. The floor area in the rice mill wher

SPL exceeded 85 dBA was identified from the noise survey map of each rice mill to determine the causes of high level

of noise. In order to study the variation in SPL in the workroom of the rice mill throughout the shift, equivalent SPL was

measured at six locations in each rice mill. The subjective response to noise in rice mills was assessed by conducting

personal interview with all the workers of the rice mills using a structured form. Demographic information, nature of

work, working hours, rest period, experience of working in mill, degree of noise annoyance, activity interference, and

psychological and physiological effects of machine noise on the worker were asked during the interview. Statistical

Analysis Used: Nil. Results: The noise survey in eight select rice mills of the major paddy-growing regions of India

ARTICLE

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Year : 2008 | Volume : 10 | Issue : 39 | Page : 55--67

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revealed that the workrooms of five rice mills had SPL more than 85 dBA in the locations where workers were engage

for most of the time. The predominant noise sources in the rice mills were paddy cleaner, rubber roll sheller,

compartment separator, rice cleaner, sieve shaker and an electric motor without enclosure. The causes of high noise i

the rice mills may be due to the use of a long flat belt drive, crank-and-pitman mechanism, absence of an electric moto

enclosure, poor machine maintenance and inadequate acoustic design of the workroom in the rice mill. In general, a

well-maintained rice mill with each machine being run individually using an electric motor produced less noise than tha

being run using a single electric motor along with flat belt drives. The normal working period in the rice mill was 48

h/week and it was 56 h/week during the peak season of rice milling. About 26% of the total workers were exposed tonoise of more than 85 dBA. Subjective response indicated that about 26% of the total workers felt noise interferes in

their work and about 49% workers were of opinion that noise interferes with their conversation. Conclusions: The

workers in the rice mills are exposed to high noise, which will have detrimental effect on their health. Apart from

undertaking appropriate noise control measures, preventive maintenance of machines needs to be given due

importance in all the rice mills.

Full Text

Introduction

India is the second largest rice-growing countries in the world with an annual production of 93 million tonnes. [1] For th

post-harvest processing of paddy, about 30,000 rice mills exist in the rural areas and most of them are owned by privatentrepreneurs. They form one of the major agro-industries in India. Most of the rice mills have high capacity and high-

speed processing machines and they are operated using either an electric motor or a diesel engine. These rice mills

employ a large number of unskilled labourers for the processing of paddy besides technical man power for repair and

maintenance of the machines. As the activities of the rice mills in India are not regulated under any legal provision, the

are considered under unorganized sector. [2] Hence, occupational health and safety cover for the workers in rice mills

non-existent. [3]

A major occupational hazard for workers in rice mills is the noise during the operation of various machines. In India,

noise in the workrooms of industries is considered as a part of the routine and inescapable industrial work environment

[3] Moreover, no industrial law in India provides any protection to workers from noise pollution. [4] Section 11 (I) of the

Factories Act, 1948 stipulates that every factory shall be kept clean, without having any nuisance. The word "nuisance

includes noise, but statutory provisions in industrial law to provide this protection are overdue. Due to this, agro

industries do not give much importance to the exposure of workers to high-intensity noise and the adoption of suitable

measures for its control. Noise is one of the common occupational hazards and there is evidence to support the

increasing prevalence of high noise levels in the workplace. [5] Therefore, one of the major safety concerns has been

the exposure of high intensity of noise to the workers.

Detrimental effect of high noise levels on human health is known for centuries. Noise disturbs work, rest, sleep and

communication and leads to accidents in industries. It causes physiological, psychological and possibly pathological

reactions. [6] Noise has been found to be the cause of higher blood pressure. [7],[8] The effect of workplace noise on

the hearing loss of workers has been a topic of debate among scientists for a number of years. [7],[8],[9],[10] Hearing

loss due to industrial noise has been studied by many researchers. [11],[12],[13],[14] In a study, Eleftheriou [11] found

How to cite this article:

Prasanna Kumar GV, Dewangan KN, Sarkar A, Kumari A, Kar B. Occupational noise in rice mil ls.Noise Health 2008;10:55-67

How to cite this URL:

Prasanna Kumar GV, Dewangan KN, Sarkar A, Kumari A, Kar B. Occupational noise in rice mills. Noise Health [serial online]

2008 [cited 2011 Jul 13 ];10:55-67

Available from: http://www.noiseandhealth.org/text.asp?2008/10/39/55/40824





that 27.8% of workers in light manufacturing industries in Cyprus suffered from permanent hearing loss. However,

hearing loss does not occur in a sudden traumatic manner, but it is imperceptibly slow and painless. [15] At first worker

are unaware of it, and gradually they notice loss of hearing. [16] International Standard Organization has set out

comprehensive information on the risk of loss of hearing in relation to age, duration of exposure and the intensity of

noise. [17] Exposure duration of 40 h/week of noise level of 85 dB(A) L eq is considered to be safe and noise levels

above this limit are bound to cause noise induced hearing loss. [18],[19]

Extensive research work has been done in Western countries on measurement of industrial noise. Czuchaj et al. [20]reported noise sources and acoustic properties of the workrooms in fat, oil and meat processing plants, breweries (foo

processing plants) and pharmaceutical industries in Poland. Pazzona and Murgia [21] observed that the annual amoun

of sound energy absorbed by the workers of the sheep farms in Sardinia, Italy, was 89.8 dB(A) L eq .

The studies conducted in Germany [22] have revealed that the mills handling cereal crops had a noise level more than

95 dBA in various workrooms. In India, noise levels of tractors, power tillers and farm machinery have been reported.

[23],[24],[25] The literature available on the noise level of workrooms in Indian industries is limited. The noise dosimetr

study conducted in a pharmaceutical factory revealed the exposure of workers to noise dose of 85 dBA. [26] The study

conducted to assess the sound levels at various locations in a factory involved with the production of wheels for four-

wheeler vehicles indicated sound-pressure level (SPL) exceeding 90 dBA in the generator room, compressor room,

assembling room and rooms where the defacing machine, induction heater, shearing machine, pressing machine,

forming machine and welding machines have been provided. [27] But no study has been conducted on the noisecharacteristics of workrooms in agro industries in general, particularly rice mills. [28]

Rice mills are important for the comprehensive development of rural economy of India. The study of noise level in the

workrooms of rice mills will present the status of noise exposure to workers so that appropriate measures can be

undertaken to minimize the noise exposure, if any. Keeping these factors in view, an investigation was undertaken with

the following objectives:

To identify the predominant noise sources and its distribution in the rice mills.To study the causes of high levels of nois

in the rice mills.To examine the response of the workers towards noise.

Materials and Methods

The study was conducted in the north-eastern region of India located between 21°57 ′ to 29°30 ′N latitude and 89°46 ′ to

97°30 ′E longitude. Agriculture is the livelihood of most of the people in the north-eastern region of India and paddy is

the major crop. To process paddy, several rice mills, mostly established by small and medium entrepreneurs, exist in

the region.

Selection of rice mills

A walk-through survey was conducted in several rice mills located in various parts of the region. It was found that the

noise in the workrooms of rice mills was louder than busy city traffic and the workers had to talk loudly to someone at 1

m away. Based on this criterion, eight rice mills established during 1980-1985 were selected. The written approval was

obtained from the owner of each rice mill for conducting noise survey in the workroom of rice mill. Furthermore, the

owners of rice mills agreed to provide the correct information on every aspect of the operation of rice mill and allow the

workers of the mill to provide the true information required for the study. Information such as output capacity, size of th

power source, maintenance condition of the machines and workroom configurations of the selected rice mills were

collected by personal observations and enquiry with the owner of the rice mill.

Tasks

The sequence of operations essentially followed in the milling of rice are: (i) feeding of paddy from gunny bags to the

dumping pit, (ii) cleaning of paddy grains, (iii) removal of husk (dehusking) from the paddy, (iv) separation of rice grain





from the husk, (v) polishing of rice, (vi) cleaning or separation of rice from bran and (vii) dumping of rice at a place for

subsequent collection in gunny bags. For cleaning of paddy, sieve shakers are used. Dehusking is done using rubber

roll shellers. For the separation of rice from the husk, a sieve shaker along with a blower is used. The rice is separated

from the paddy and broken rice using a compartment separator. Polishing is achieved through a cone-type polishing

machine (rice polisher) and the rice is cleaned finally using a sieve shaker along with a blower. The paddy/rice is

transferred from one machine to the next using bucket elevators. The sequence of processing machines through which

the paddy flows during milling is shown in [Figure 1]. The dotted lines indicate other optional machines used in various

rice mills. The paddy cleaner, husk separator, compartment separator and rice cleaner require reciprocating motion,whereas the rubber roll sheller, rice polisher, blower and bucket elevator require rotary motion. From the power source

the reciprocating motion is supplied using crank-and-pitman mechanism, whereas the rotary motion is supplied throug

a flat belt drive. The source of power for all the machines and bucket elevators is the three-phase induction motor.

Either each machine is operated from an individual electric motor or all the machines are operated through a flat belt

drive from a long shaft coupled to an electric motor.

Experimental conditions

The study was conducted during March and April, which was just after the peak period of paddy milling in the region.

The normal working hours of the rice mill are from 0700 to 1700 h with a lunch break from 1200 to 1400 h. During the

peak period, the paddy milling is also done in night shifts from 1900 to 0500 h with a rest period from 2200 to 0000 h.

Each rice mill employed two types of workers, viz. , permanent and contract. Permanent workers were employed for aperiod of one year, whereas contract workers were engaged only during the peak period of milling. In the night shift,

about 50% of the permanent male workers of the day shift are engaged. The contract workers are employed in both

shifts to meet the rest of the man power requirement for the operation of mill. The noise data were collected between

0800 and 1200 h. The average temperature and relative humidity during the period of investigation in the workrooms o

the mill were 25 ± 2°C and 74 ± 3%, respectively.

Experimental procedure

The guidelines of Canadian Centre for Occupational Health and Safety (CCOHS) were followed during the noise

survey. [29] Grid points were marked on the floor of the workroom of the rice mill at a spacing of 1 m × 1 m. The (0,0)

coordinate was appropriately taken on the extreme left hand corner of the mill. In case the machines in the mill

interrupted with the grid points, grid points were marked on either sides of the machine. The coordinates of the

rectangular area under each machine were noted down to mark the location of machines in the mill. A sketch showing

grid points for the noise measurement and the location of various machines in the mill was drawn. The machine, which

has been placed above another machine, was drawn using dark dashed lines in the map. A sound level meter (SLM;

Model-824; Larson and Davis, USA) was used to record noise levels. The SLM was calibrated before the start of the

study. To record data, it was held at arm's length and about 1.5 m above the floor so as to prevent the shielding of nois

by the operator and other objects. The direction of the SLM was towards the nearby noisy source. The SPL in weightin

scale "A" and the noise spectrum were recorded at each grid point for 30 s and data were stored in SLM. To increase

accuracy, two replications were taken at each grid point. A noise survey map of equivalent SPL was drawn for each ric

mill by drawing contour lines on the sketch of the rice mill between the points of equal SPL. The floor area in the rice

mill where SPL exceeded 85 dBA was identified from the noise survey map of each rice mill to determine the causes o

high levels of noise.

In order to study the variation in SPL in the workroom of the rice mill throughout the shift, equivalent SPL was measureat six locations in each rice mill. The six locations were appropriately taken with one each near the paddy feeding pit

and the rice outlet and other four in front of the four major noisy machines of the mill, where workers were engaged

during its operation.

Assessment of subjective response

Before the noise survey in each rice mill, a meeting was conducted with all workers of the day shift. The purpose of the

noise survey and its application in improving their working environment were convinced in the meeting. During the rest

period, a subjective response to noise was assessed with personal interview of each worker separately. Demographic





information, nature of work, working hours, rest period, experience of working in mill, degree of noise annoyance,

activity interference, and psychological and physiological effects of machine noise on the worker were asked during th

interview. These details were noted in a structured form.

Results and Discussion

The details of the rice mill, viz ., output capacity, size of the electric motor, floor area of the mill, floor area under the

machines, number of bucket elevators and maintenance level of the machines are presented in [Table 1]. All the

machines and bucket elevators of the rice mills 1-6 were driven by a single electric motor. Each machine and bucket

elevator of the rice mills 7 and 8 were driven by individual electric motors. In addition, all the machines of these two ric

mills were placed on a foundation of 1.2-m height. The materials used for the rice mill building are given in [Table 2].

Demographic characteristics of the study population

The workers were in the age group of 26-56 years. The mean age of all the workers was about 42 years. They had 5-2

years of work experience in the rice mill. About 42% of the workers were female. All the labourers work on an average

56 h a week (8 h/day, 7 days a week) during the peak period of rice milling and 48 h a week (8 h/day, 6 days a week)

during the rest of the period in a year. The distribution of labourers in each rice mill during the day shift is presented in[Table 3]. Male workers were employed mainly for the heavy task of paddy feeding near the paddy feeding pit and the

collection and storage of rice in gunny bags at the rice outlet. Female workers were employed at the rest of the

locations because the work was light and their wages were less as compared to male workers.

Noise survey map of workroom

The noise survey map of the workroom of rice mills is presented in [Figure 2],[Figure 3],[Figure 4],[Figure 5],[Figure 6],

[Figure 7],[Figure 8],[Figure 9]. The map of the workroom of rice mill 1 indicates that the SPL of 89 dBA was

concentrated in the floor area between the rubber roll sheller and the power transmission shaft, where a long flat belt

drive is provided to operate the sheller. Moreover, the SPL of more than 85 dBA is found behind the paddy cleaners an

the compartment separator. Both these machines require reciprocating motion using crank-and-pitman mechanism.

Although 30% of the total floor area of the rice mill had SPL of more than 85 dBA, it had no adverse effect on laboureras they did not work in this zone. A similar trend was observed in rice mill 2, except that the labourer working in front of

the rubber roll sheller was exposed to the noise of more than 85 dBA. Furthermore, the floor area under the SPL of

more than 85 dBA was found to be about 50% of the total floor area of the mill. This was owing to the absence of

enclosure to the electric motor and poor maintenance of various machines in the mill.

In rice mills 3 and 4, the floor area with SPL of 85 dBA was found to be about 60 and 80% and of the total floor area of

the respective rice mills. This included mainly the floor area under the electric motor, the auxiliary sieve shaker and the

long power transmission shaft. In rice mill 3, only the labourers working in front of the paddy cleaner, rubber roll sheller

and sieve shaker were exposed to high noise above the acceptable limit. But in rice mill 4, all the labourers were

exposed to high noise. This may be due to the use of a long flat belt drive, crank-and-pitman mechanism, absence of a

electric motor enclosure and lack of regular maintenance of the machines in the rice mill. Furthermore, rice mill 3 had

higher capacity electric motor and more number of bucket elevators as compared to those in other mills. The reflective

GI sheet material used for the wall might have also contributed to the high noise.

In rice mills 5 and 6, the SPL was within acceptable limits in the working zone of the labourers. The owners of these ric

mills had given due importance to the maintenance of the machines in the rice mill, which may be the reason for low

levels of noise. However, the capacity of rice mill 6 (1000 kg/h) was more than that of rice mill 5 (800 kg/h). A rice hulle

in addition to the rice polishing machine was used in the rice mill 6. Furthermore, the floor area of rice mill 6 (384 m 2 )

was lower than that of rice mill 5 (285 m 2 ). These might have contributed to the slightly higher levels of noise in rice

mill 6 than that of rice mill 5.

All the machines and bucket elevators of rice mills 7 and 8 were operated separately by small electric motors. In





general, a well-maintained rice mill with this arrangement of power supply to the machines produced less noise than

that with power supply from a single electric motor using several flat belt drives. In addition, all the machines of these

mills had been fitted on a deep foundation, which absorbed the machine vibration leading to low noise. In rice mill 7, th

floor area under SPL of more than 85 dBA was concentrated around the sieve shaker and the paddy cleaner. In rice m

8, it even extended to the area around the paddy feeding pit and the rice cleaner covering about 80% of the total floor

area of the mill. The high noise in these two rice mills may be due to crank-and-pitman mechanism used on the sieve

shaker, paddy cleaner and rice cleaner. The maintenance condition of machines of rice mill 8 was moderate, which

might have also caused high noise.

Thus, the predominant noise sources in the select rice mills were found to be the paddy cleaner, rubber roll sheller,

compartment separator, rice cleaner, sieve shaker and an electric motor without enclosure. The causes of high noise

levels in rice mills may be attributed to the use of a long flat belt drive, crank-and-pitman mechanism, absence of an

electric motor enclosure, poor machine maintenance and inadequate use of acoustic materials for noise control in the

rice mill. The study conducted in Germany [22] has also revealed similar facts with noise levels of 105, 100, 105 and

108 dBA, respectively in the floor area separator, sifter, roller and huller. In these machines, the similar kind of

mechanisms as reported in the present study is used for the power transmission. However, in the present study,

besides other technical factors, the poor maintenance of machines and the use of inadequate acoustic material on the

walls of the workrooms had resulted in excessive noise. Czuchaj et al. [20] attributed use of sound-reflecting walls

without any acoustic adaptations as the cause for high noise in the workrooms of fat, oil and meat processing plants

and pharmaceutical industries in Poland.

Variation in SPL during a shift and frequency analysis

The labourers were exposed to continuous noise in the rice mills. The overall noise level in the rice mills ranged

between 78 and 92 dBA. As an example, the variation in daily noise exposure of the labourers in rice mill 4 working

near the paddy feeding pit and the rice outlet throughout the work shift is presented in [Figure 10]. [Table 4] presents

SPLs in the working zones of various machines in the mill. It can be seen that the workers engaged near the auxiliary

sieve shaker in the rice mills were subjected to higher levels of noise than those engaged in other locations. The

distribution of the total subjects by equivalent continuous noise level per shift, presented in [Table 5], reveals that in

each shift, a total of 32 labourers accounting for 26% of the total labourers involved in all the rice mills were exposed t

noise level of more than 85 dBA. This group of workers included 11 women.

The frequency analysis of SPL (L eq ) of 1/3 octave band in the working zone of the workers at various locations in ric

mills 1 and 7 are presented in [Figure 11]. In rice mill 1, characteristics of noise at all locations were similar. SPL of the

rubber roll sheller was high, whereas the SPL at the rice outlet was low at most of the frequencies. Above 3150 Hz, th

noise level at all the locations decreased. The most dominant noise were observed at 80 Hz near the paddy feeding pit

paddy cleaner, rubber roll sheller and rice outlet. For compartment separator and rice polisher, most dominant noise

was found to be at 16 and 12.5 Hz, respectively. Thus, the peak SPL was found to be near the oscillation or rotation

frequency of individual machines near each location. In rice mill 7, near the paddy feeding pit and the paddy grain

cleaner, the most dominant noise was observed at 40 Hz, whereas near the rubber roll sheller, the same was observe

at 63 Hz. Thus, for these three machines, the dominant noise was at slightly lower frequency than in rice mill 1. Near

the rice polisher, the most dominant noise was at 100 Hz, whereas near the compartment separator and the rice outlet

the same was observed at 200 Hz. Thus, for these three machines, the dominant noise was at higher frequency than i

rice mill 1. The slight shift in peak SPL may be due to the type of power supply used for the operation of the mill. All th

machines of rice mill 1 were operated by a single electric motor, whereas each machine of rice mill 7 was operated byindividual electric motor.

Subjective response of the noise

The results of the subjective response to noise in the rice mills illustrated the risk of hearing damage among the

workers, particularly working near the predominant noise sources [Table 6]. About 26% workers said that noise

interferes in their work and about 49% workers were of opinion that noise interferes with their conversation. This is

found to depend on the distance from the peak noise source. About 6% said that noise makes them angry/upset.

However, physiological effects were considered less significant. About 11% stated that it harms their hearing and 8%





stated that it gives them headaches.

Conclusions

The noise survey in the eight select rice mills of the major paddy-growing region of India revealed that the workrooms

the five rice mills had SPLs more than 85 dBA in locations where workers were engaged for most of the time. The

predominant noise sources in the rice mills were the paddy cleaner, rubber roll sheller, compartment separator, rice

cleaner, sieve shaker and an electric motor without enclosure. The causes of high noise in the rice mills may be due to

the use of a long flat belt drive, crank-and-pitman mechanism, absence of an electric motor enclosure, poor machine

maintenance and inadequate acoustic design of the workroom of the rice mill. In general, a well-maintained rice mill wi

each machine being run individually using an electric motor produced less noise than that being run using a single

electric motor along with flat belt drives. The normal working period in the rice mills was 48 h/week and it was 56 h/we

during the peak season of rice milling. About 26% of the total workers were exposed to noise of more than 85 dBA.

Subjective response indicated that about 26% of the total workers felt noise interferes in their work and about 49%

workers were of opinion that noise interferes with their conversation. Apart from undertaking appropriate noise control

measures, preventive maintenance of machines needs to be given due importance in all rice mills.

Acknowledgement

The authors are thankful to the owners and workers of the rice mills for their cooperation during the course of data

collection.

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