Risk Assessment of Hand-Arm Vibration Exposure in Jackhammer Operators: The Influence of the Equipment and Working Surface

Miguel, A. S.

Ergonomics Laboratory/University of Minho/Guimaraes, Portugal

+351 253 510 369 / asmiguel@dps.uminho.pt

Arezes, P. M.

Ergonomics Laboratory/University of Minho/Guimaraes, Portugal

+351 253 510 354 / parezes@dps.uminho.pt

Melo, Rui B.

Ergonomics Department/Technical University of Lisbon/ Portugal

+351 214 149 128 / rmelo@fmh.utl.pt

Costa, N.

Ergonomics Laboratory/University of Minho/Guimaraes, Portugal

+351 253 510 367 / ncosta@dps.uminho.pt

Braga, C.

Ergonomics Laboratory/University of Minho/Guimaraes, Portugal

+351 253 510 367 / cbraga@dps.uminho.pt

ABSTRACT

ABSTRACT

Health and safety researchers and practitioners are increasing their attention on occupational exposure to vibration. The construction sector presents several activities with exposure to vibration. Jackhammers present one of the primary sources of occupational exposure to hand-arm vibration, mainly because of the frequency and intensity of use.

The present study aimed at characterising the profile of exposure to hand-arm vibration by jackhammers operators in the construction sector. Vibration levels were evaluated during real work tasks, involving demolitions and pavement breaking. Measurements were made according to ISO 5349:2001 standard. Symptoms were found in only 20% of the workers. Lower ahw (rms) values were found in electric jackhammers, although with relevant differences for equipments with different weight category, when compared with pneumatic powered tools. Differences between the working surface materials (concrete, stone and masonry) were also found.

Keywords

Keywords

Vibration, risk assessment, construction

INTRODUCTION

INTRODUCTION

The construction sector presents some unique characteristics that distinguish it from all others sectors of activity. Its seasonality, the variability of the tasks and the insufficient professional training contribute to a high risk of accident occurrence and professional diseases development. Amongst those risks is the exposure to hand-arm vibrations (HAV).

According to the Portuguese Institute of Statistics (INE), in 2003 the construction sector had 109,000 companies, mainly composed of small and medium companies, which represented 17% of the Portuguese productive sector [5].

Regarding vibration exposure, the hand-arm vibration syndrome (HAVS) is well identified as a consequent pathology. Neurological, vascular and oesteoarticular disorders are also commonly associated. According to the references in the European Directive, a worker whose daily exposition to HAV exceeds 2.5m/s2 for 12 or more years, has 10% of chance of developing HAVS [1,2].

Although it is not well established, it is possible to find a relation between the exposure levels and the time of exposure to HAV. This relation is based on the vascular effects, mainly because they are the largely studied and also the more easily recognised ones [3].

Figure 1 shows the daily vibration exposure A(8), which is estimated to produce finger blanching in 10% of exposed persons. Values are shown for group mean total (lifetime) exposures from 1 to 10 years.

Figure 1 - Vibration exposure for predicted 10% prevalence of vibration-induced white finger in a group of exposed persons.

The values in figure 1 and expression 1 are derived from studies of groups of workers exposed to tool vibration magnitudes up to 30 m/s2 in their occupations for up to 25 years. Almost all studies involved groups of persons who performed, near- daily and work involving one type of power tool or industrial process in which vibration was coupled to the hands. The acceleration values are derived from studies in which the dominant, single-axis, frequency-weighted component acceleration was reported [3].

 a ⋅T 2

C = h F 95 ⋅ 100(1)

Where C is the percentage of exposed persons estimated to produce finger blanching (10<C<50%), ah the frequency-weighted acceleration in m/s2, and TF the previous exposure time (<25 years).

METHODOLOGY

Primarily, seven companies of the construction sector were consulted to determine how many workers were exposed to hand-arm vibration induced by jackhammer operations. Then, these workers filled out a questionnaire to assess the history of exposure to vibration at the workplace and in other non-work related situations. This questionnaire also inquired about the health condition of the workers and past incidents or health problems.

Technical spreadsheets of the jackhammers models were created in order to compare power sources, output powers, vibration reducing devices and other technical issues.

Vibration exposure levels assessment was carried out during real work tasks, involving demolitions and pavement breaking. Measurements were made according to ISO 5349-1:2001 and ISO 5349-2:2002 standard [3,4]. For this evaluation a vibration real time analyser from Svantek (model SVAN948) was used along with a tri-axial accelerometer (DYTRAN 3023). The accelerometer typical mounted resonance frequency is high enough to minimize the dc shift effect [8]. The mounting of the accelerometer on the equipments handle followed the specifications of the annex A and D of ISO 5349-2:2002 [4].

RESULTS AND DISCUSSION

The average age of the workers was 40 years (±11), with a history of more than 10 years average professional exposure to vibrations. Only 20% of the workers claimed to have HAVS, being the most common referred symptoms the periodic numbness and pain in fingers, paresthesia, and pain in wrists and hands.

Malchaire et al.[6], in a 3-year prospective epidemiological study conducted to investigate the relationship between musculoskeletal complains and sensorineural complains of workers exposed to vibrations estimated the risk of serious sensorineural complains of about 6% at 2.5m/s2 and of about 10% at 5m/s2 (weighted personal exposure acceleration). Also according to NIOSH, the biological effects of vibration exposure may be influenced by many non-vibration factors, including the following: exposure pattern; length and frequency of work and rest periods; magnitude and direction of forces applied to the work piece by the operator; body posture and orientation of the wrists, elbows, and shoulders; area of hand exposed to vibration; climatic conditions; worker’s skill and work practices; hand covering; maintenance of equipment; noise (possible synergistic effect); use of tobacco, some drugs, and some chemicals [7].

Electric and pneumatic powered jackhammers are similar tools, however they have differences in terms of output power and weight. As result of these differences, these tools are used for different work tasks in construction sites. Electric jackhammers are used to open small ducts on concrete and masonry to carry power cables and water pipes. By their turn, pneumatic jackhammers are usually used in more power demanding work tasks, like removing pillar heads, exposing steel armours and demolitions of concrete and rock blocks. It was found the need to divide electric jackhammers in two different groups, the ones that weighted less than 8 kg and those whose weight was above 8 kg. These two groups of electric powered tools have different output powers.

Lower ahw (weighted acceleration) values were found in electric jackhammers when compared with pneumatic powered tools (see table 1). This appears to be a direct result of the differences in the output power, but it can also be consideredthat the active vibration reduction mechanisms, installed in the electric tools, contribute for this outcome.

hv

Another relevant outcome of this study are the observed differences between the working surface materials. These differences are significant between concrete/stone and masonry, for the same type of tools (electric powered under 8 Kg). At the construction site it was observed that the jackhammers were held with a 45º angle (to the vertical) to perform tasks in masonry, and this working surface was less resistant than concrete. The first observation leads to less grip and push power by the operator and the second may allow the tool to produce more acceleration.

By their turn, when the values obtained for electric powered tools above 8 Kg in different work tasks (concrete versus rock) are compared, almost no difference in the ahw is observed, but a much more significant difference in the peak value is registered. This fact can be explained by the differences in resistance of those working surface materials.

Table 2 shows a resume of the A(8) levels, considering the average vibration levels of the power tools and the average time exposure.

Power

Supply Weight

≤ 8 Kg

Daily exposure time

Surface materials

Cement Masonry Rock A(8) A(8) A(8) 5.41 9.38 --

Electrical > 8 Kg 2h

8.14 -- 9.00

Pneumatic > 20 Kg 11.34 -- --

Table 2 – Characterization of the average exposure time for jackhammer operators, vibracional levels A(8) (in m/s2), as function of the type of jackhammer and surface materials.

The daily vibration exposure A(8) of every tool and surface presented in table 2 exceeds de 5 m/s2 limit for HAV exposure. Therefore the risk of HAVS exists and can be estimated.

Risk assessment can be accomplished by using expression 1, for one third of the exposed population. The estimation of the number of exposure years sufficient to produce finger blanching is presented on figure 2.

12

C1 ≤ 8 Kg Cement10

C2 > 8 Kg Cement

8       Y                                                                                                      C3  > 20 Kg Cement6       a                                                                                                       A1  ≤ 8 Kg Masonryrs                                                                                                       R1  > 8 Kg Rock4

2

0

C1 C2 C3 A1 R1

Figure 2 – Exposure time (in years) until 33% of the operators produces HAVS, as function of the power tool and surface materials.

Exception made for condition C1, related with jackhammers with less than 8Kg and tasks developed on cement surface, in all other conditions it is expectable that 33% of the studied jackhammer operators present HAVS, like finger blanching, in less than 10 years.

CONCLUSIONS

The selection of the tool needs to take in account the specifications of the task and the working surface. Most of the work tasks encountered can be accomplished by smaller and less hazardous jackhammer.

The risk of HAVS in the construction sector, mainly amongst jackhammer operators, is very high, mainly due to tool vibracional levels, the work tasks and the number of years of exposure.

BIBLIOGRAPHY

• 1. DecretoLei n.º 46/2006, de 24 de Fevereiro – Prescrições  mínimas  de protecção da saúde e segurança dos trabalhadores em caso de exposição aos riscos devidos a agentes físicos (vibrações).
• 2. Directiva n.º 2002/44/CE, de 25 de Junho Riscos devidos aos agentes físicos (vibrações) (décima sexta directiva especial na acepção do n.º 1 do artigo 16.º da Directiva 89/391/CEE).
• 3. EN ISO 53491:2001 Mechanical vibration – Measurement and evaluation of human exposure to handtransmitted vibration. – Part 1: General requirements.
• 4. EN ISO 53492:2002 Mechanical vibration — Measurement and evaluation of human exposure to handtransmitted vibration — Part 2: Practical guidance for measurement at the workplace.
• 5. INE (2004), Anuário Estatístico de Portugal – 2003, Lisboa.
• 6. Malchaire, J., Piette, A., and Cock, N., (2001), Associations between HandWrist Musculoskeletal and Sensorineural Complains and Biomechanical and Vibration Work Constrains”, Ann. Occ. Hyg. 45, 479491.
• 7. NIOSH – National Institute for Occupational Safety and Health (1989), Criteria for a recommended standard: Occupational Exposure to HandArm Vibration, edited by Division of Standards Development and Technology  Transfer, Cincinnati, Ohio.
• 8. Ruiz, R. M. C., & Muñoz, B. L., (1999), Exposición a vibraciones en el lugar de trabajo, Instituto Nacional de Seguridad e Higiene en el Trabajo, Ministerio de Trabajo y Asuntos Sociales, Madrid.