Summary

Portable nail guns, or nailers, drive in nails by means of an impact or hammering force. Workers who use them are exposed to impulse noise and vibration, as the guns generate very high levels for very short periods of time. Exposure to impulse noise and vibration creates a risk of developing occupational diseases. Discussions with the Association paritaire pour la santé et la sécurité du travail du secteur de la construction [construction sector OHS association], known as ASP Construction, confirmed that this type of tool is very widely used by construction workers, who are among the top five groups in Quebec for number of compensation awards for occupational hearing loss. Less noisy nail guns that transmit less vibration to the handle therefore need to be selected and designed. This is a difficult thing to do, as very little information exists on the noise and vibration levels associated with these tools or on how to reduce them.

There were three objectives to this research project: (i) determine whether the existing standards for noise (EN 12549) and vibration (ISO 8662) could be used to measure noise and vibration levels in the lab comparable to those measured in the field; (ii) develop and use noise and vibration source diagnostic methods in the lab; and (iii) come up with possible solutions to the problem of nail gun noise and vibration.

(i) Comparison of field and laboratory measurements. For the purposes of this first objective, 10 commercial nail guns were selected: eight framing nailers, including one electric (battery-operated) model, one gas (butane) model and six pneumatic models, and two pneumatic roofing nailers (asphalt shingles). Vibrations were measured in the lab and in the field using a triaxial accelerometer secured to the nailer handle. For noise, the sound power was measured in the lab on a standardized test bench (STB) consisting of nine microphones (cube grid), while for the field measurements, the level of exposure at the worker’s ears was measured using two microphones placed on the person’s ear protectors. The field measurements were done using a portable data acquisition system in a small backpack, which allowed the operator to continue to work as usual. The comparison of noise levels measured in the field and in the lab showed that the acoustic dispersion of the workpiece during the field measurements can contribute to the overall level (maximum of 3.5 dBA more than the laboratory measurements), but that this dispersion does not change, or barely changes, the ranking of the nail guns by noise level. For vibration, the ranking of the nailers by vibration levels was similar in the field and the lab. This justified using the STB in the lab to rank the nail guns.

(ii) Diagnostic methods and sources. According to the current standards, the measurements used to rank nailers require three operators to drive in over 50 nails each. This procedure takes a huge amount of time and complicates the work of diagnosing noise sources. To simplify the procedure, an operator substitution device (OSD) consisting of a support, a system replacing the worker’s hand and arm, and a remote trigger was devised. The OSD was validated, and the results showed that, for a series of tests performed with only 10 nails, the variability in results was similar to that obtained with the STB requiring three operators and a total of 150 nails. In comparison with the STB results, the mean acceleration obtained with the OSD was slightly overestimated (0.5 m/s²), while the sound power levels were slightly underestimated

(approximately 1 dB). Nevertheless, these differences, though not desirable, did not change the ranking of the nailers by noise or vibration level. Furthermore, this system can rank a nailer in less than 30 minutes.

The diagnostic methods used to determine noise sources were sound-source masking (enclosures), acoustic imaging and noise/image synchronization with a high-speed camera. The use of a modified test bench also made it possible to assess the contribution of the acoustic dispersion of the workpiece to the total noise produced by the nailer. The three main noise sources are the nailer body, the exhaust system and the workpiece. For pneumatic nailers, the greatest amount of noise is generated by the nailer body; it reaches levels equivalent to those of the exhaust system, while the electric nailer and the gas nailer do not produce any exhaust noise. As vibration is transmitted to the operator through the handle, only the body of the nail gun contributes to the vibration levels. The electric nailer generated vibration levels equivalent to those of the pneumatic nailers, whereas the noise levels were approximately 10 dBA lower. The contribution of the workpiece is significant and of an order of magnitude equivalent to the exhaust noise or the noise from the nailer body. The vibration of the nailer was practically constant and was not influenced by the workpiece.

(iii) Possible solutions. Possible ways to help reduce the three main sources of noise are presented. For pneumatic nailers, adding a silencer is strongly recommended. Also, to reduce the dispersion of the noise from the nailer body, it is suggested that an acoustic barrier be added. Last, solutions focusing on how the nailer works are also proposed. For vibration, the main solution consists in separating the handle from the nailer. Given that the vibrations of maximum amplitude are generated when the mobile part (hammer) that drives the nail reaches the stop, efforts to optimize the travel stops (low and high) of the hammer mechanism would seem worthwhile. Furthermore, as the amount of energy used to drive in a nail is constant, regardless of the nail used and the material being nailed into, in some cases a certain amount of superfluous energy needs to be dissipated. That superfluous energy probably contributes to the noise and vibration and could be reduced if the amount of energy used to drive in the nails were adjustable.

In the course of this study, several mechanisms involved in generating noise and vibration when portable nail guns are used in the construction industry were identified and quantified. The study also led to the development of an operator substitution device used for laboratory testing. This device still requires further development and optimization in order to more accurately approximate the values obtained by operators, but its low variability means that only 10 nails are needed to rate a nail gun. An optimized OSD could replace the three operators required under existing standards and thereby greatly simplify nail gun assessments, while facilitating manufacturer use of test benches to measure the noise and vibration levels of their nailers.