Fighting noise and vibrations
|Danuta Augustyńska, Ph.D. (Eng.)
Dariusz Pleban, Ph.D.(Eng.)
Ph.D. (Eng.), D.Sc. (Eng.)
The main directions of the Department’s activities since its establishment have been:
As a result of work carried out during the first period of activity, methods of noise measurement at workstations and methods of testing noise source (machinery) have been developed. The results of this work have been implemented in Polish standards, regularly amended pursuant to international standards, and made it possible to design and build a reverberation room and an anechoic chamber at the Institute, some of the first in the country. Methods and test stands have been developed to measure and record vibrations at workstations, methods of testing ultrasonic devices and guidelines for designing screens and enclosures for such devices, silencers for fluid flow machines and combustion engines (patent no. 66348). In addition, prototypes of a vibration perception meter (patent no. 57064) and of a typical soundproof cabin intended for rooms with high noise levels, and other solutions of collective protective equipment (screens and casings). During that period, the Department also developed methods of measurement and assessment of the infra– and ultrasonic noise hazards in the working environment. The results of the work provided a grounding for the development of documentation and the definition of infra– and ultrasonic threshold limit values (TLVs). The Laboratory of Active Methods of Noise Reduction and special test stands were established as a result of Professor Zbigniew Engel’s initiative, primarily aimed at the active reduction of noise levels in waveguides. In 1988, the Institute, in cooperation with the Department of Mechanics and Vibroacoustics of the AGH University of Science and Technology, organised Poland’s first seminar on active methods of noise and vibration control.
In the years 1990-2001, following the relocation of the Institute’s head office and the establishment of new laboratories, research was undertaken aimed primarily at the development of methods and stands for machinery certification testing, as well as personal and collective equipment for noise protection (hearing protection, gloves protecting against vibration, cabins for operators of machinery and equipment) compliant with occupational safety and ergonomics requirements consistent with the requirements of European directives and standards. Research was also carried out into active methods of noise reduction, methods and guidelines for designing acoustic emergency signals compliant with machinery directive requirements and European standards, as well as methods of assessment of the occupational risk associated with exposure to noise and mechanical vibration.
The research resulted in the development of methods and stands, unique in Poland, to test the acoustic and mechanical properties of hearing protection. They enable the conformity assessment of hearing protection devices with the requirements of Directive 89/686/EEC, and thus the successive elimination of hearing protection devices not meeting those requirements from the Polish market.
Moreover, methods and stands unique in Poland and Europe were developed to test materials and gloves used for protection against mechanical vibration according to European standards. The methods and stands, verified during tests conducted jointly with the notified Laboratory of Vibration at the BGIA Institute (Institute for Occupational Safety and Health), Sankt Augustin, Germany, enable testing compliant with the European system of product conformity assessment. In turn this allows for the selection of anti-vibration gloves that comply with European standards and the rejection of products that are inefficient or even reinforce vibrations from several types of domestic and foreign gloves on the market. The authors of the stands received the 1st level award in the National Competition of Working Conditions Improvement (1997) in the category of scientific and research work applied in practice in employing establishments.
The Department has also developed new solutions for personal protective equipment against noise, including a model of earmuffs with an electronic system of active noise reduction and internal communication, FASER N1 independent earmuffs and FASER H1 helmet-mounted earmuffs, FASER N1-E3 level-dependant earmuffs, featuring increased absorption levels in line with increasing noise level in the working environment (the Brussels Eureka 2002 silver medal), and DOBOS 3 hearing protection devices selection software. The Department developed, and the Spółdzielnia Usług Techniczno- Handlowych i Wdrożeń ‘Orpel’ (Technical and Commercial Services and Implementation Cooperative) launched the production of the new ORPEL AV-1 anti-vibration gloves which, as one of the few in Poland and abroad, comply with the EN ISO 10819, EN 420 and EN 388 standards with respect to protective and usable properties.
Since 2002, the aim of the research conducted at the Department of Vibroacoustic Hazards is the modernisation and improvement of the methods and means used in the prevention of occupational damage to hearing and of vibration disease, and the reduction of exposure to noise and vibrations to bring them in line with regulations in other European Union countries. The research focuses on the development of methods for assessment of occupational risk associated with exposure to noise, infra– and ultrasonic noise, and mechanical vibrations, and the verification of TLVs for these factors. It also involves the assessment of occupational risks arising from poorly defined hazards, such as those associated with whole-body vibrations and with impulse noise, as well as the checking and monitoring of occupational risk at workstations in the state sector and enterprises where the exposure to noise and mechanical vibrations is the greatest.
Another research direction is the improvement in methods and means of noise and vibration reduction at their root by implementing new technologies, silent-running machinery and selecting means of vibroinsulation, collective and personal protective equipment including sound-absorbing and insulating machinery enclosures, sound-absorbing remote control cabins, acoustic screens, electronic hearing protection devices (active, with adjustable suppression level and communication), anti-vibration gloves, and organisational solutions. Furthermore, the research focuses on the development of active methods for noise reduction. Improvements in the level of social knowledge and awareness of noise and mechanical vibration hazards, as well their prevention, are facilitated by the development of modern information systems and databases (made available on the Internet).
The results of the abovementioned research include the analysis of occupational risk associated with exposure to noise and mechanical vibration at workstations on public transport, using dosimetry test methods, and purposemade measurement systems (vibration exposure meters). The resulting database, ‘Vibrations and noise on public transport’, was uploaded to the Central Institute for Labour Protection –National Research Institute’s website. A method for measuring and assessing mechanical vibrations (whole-body and handarm) and noise has been developed. Field testing of mechanical vibrations and noise on selected means of road transportation were conducted. Moreover, a method for testing and assessing the occupational risk associated with road transportation drivers’ exposure to infrasonic noise was developed, and a standard PN-N-01338 Infrasonic noise. Recommended values of sound pressure levels. Requirements towards measurements was drafted.
Within active noise reduction methods, a laboratory system for reducing low-frequency noise of a stationary nature was developed (software and technical documentation), utilising genetic algorithms which are based on natural selection mechanisms through seeking the best solution. Prototypes and technical documentation for three solutions permitting low-frequency noise reduction in industrial soundproof control cabins were also developed – a system to develop spatial silence zones, digitally-controlled active earphones, and an active headrest. Additionally, software used in experimental simulation of the impact of causality on the parameters of active noise reduction systems was developed, and recommendations towards non-causal systems of active noise reduction systems were formulated. A model (including software) of a system of active reduction of noise emitted by vibrating machinery parts was also developed, containing intelligent (piezocomposite) material elements.
Regarding new methods of testing and assessment of hearing protection efficiency, a test stand and Matlab procedures used to analyse the time course of acoustic signals for the purpose of testing impulse noise suppression by hearing protective devices were developed, including earplugs for various geometries of the auditory meatus. Procedures for examining impulse noise suppression efficiency during concurrent application of earmuffs and earplugs were also developed for the purposes of laboratory and workstation testing. In addition, procedures for testing of properties of earplugs were also developed during actual exposure to noise.
Research currently being conducted at the Department focuses on the following: the determination of criteria for assessing the efficiency of personal protective equipment against mechanical vibrations for different types of manual tools; the development of methods for modelling the efficiency of anti-vibration gloves using artificial neural networks; the development of methods for selecting hearing protection devices for employees exposed to impulse noise; the development of procedures determining sound power level of technological ultrasonic devices; the determination of the impact of ultrasonic noise on cognitive function of people whose work requires high levels of concentration; the design of a measurement stand to study ultrasonic noise as applied to a source emitting ultrasonic noise of stable and high sound power; the development of methods for assessing professional musicians’ exposure to noise and rules for its reduction; the assessment of exposure to school noise and of the principles of prevention; and the assessment of the exposure to mechanical vibration by quartermasters.
Other research directions include: the development of an adaptive acoustic road signal capable of recording noise data; the formulation of principles for predicting noise emissions by machinery and equipment based on the global acoustic quality indicator; modelling of the acoustic parameters of workplaces to ensure speech comprehension and acoustic signal perception by people with hearing– and sight– impairment; the development of a model for a semi-active system of reduction of mechanical vibrations at workstations; the application of neural networks in active noise reduction systems taking non-linear phenomena into account; development of genetic algorithms aimed at minimising occupational risks associated with noise exposure; the determination of the impact of the differences in complex absorption characteristics of hearing protection devices on their efficiency; the assessment of noise hazards among musicians using earplugs; the development of a variable absorption and insulation model for an active sound-absorbing and insulating system; and the development of a system signalling exceeded permitted values for noise under the ear cups of earmuffs.