Noise disturbances in daycare centers before and after acoustical treatment.
Noise is defined as any type of sound, independent of loudness, that may produce an undesired physiological or psychological response in an individual and that may interfere with the social activities of an individual or group (Bistrup, 2001). The World Health Organization (WHO) Guidelines for Community Noise (Berglund, Lindvall, & Schwela, 1999) recommend a maximum background sound pressure level (SPL) of 35 dB equivalent continuous A-weighted sound pressure level (LAeq) in preschools. The reverberation time should be about 0.6 seconds and preferably lower for hearing-impaired children (Berglund et al., 1999). For outdoor playgrounds the SPL of noise from external sources should not exceed 55 dB LAeq. In bedrooms in preschools an indoor guideline value of 30 dB LAeq for continuous noise and 45 dB maximum A-weighted sound pressure level (LAmax) for single sound events is recommended during sleeping hours (Berglund et al., 1999; Swedish Standard, 2001). The Swedish recommendations correspond fairly well with the recommendations by WHO. The Swedish National Board of Health and Welfare recommends a maximum indoor background SPL of 30 dB equivalent continuous A-weighted sound pressure level within time T (LAeq,T) for noise without audible components in preschools and a level of 25 dB Laeq,T for noise with audible components. The aim of our study was to examine perceived noise-related problems and subjective complaints in personnel in Swedish daycare centers before and after acoustical treatment.
The acoustic quality of a room at a daycare center is influenced by the building materials, the absorbency of the surfaces, the furniture, and the size and design of the room (Bistrup, 2001). Background noise levels and reverberation time must also be considered (Shield & Dockrell, 2003; Swedish Standard, 2001). Noise is generated not only by the children and the personnel at daycare centers but also by the ventilation system, heat pumps, plumbing system, dishwashers, kitchen fans, vacuum cleaners, computers, and from outdoor traffic (Shield & Dockrell, 2003).
The literature about noise problems in daycare centers is scarce. A Canadian study found noise exposure levels exceeding 75 dB LAeq,8h in four out of seven settings (Truchon-Gagnon & Hetu, 1988). The dominant determinant of the noise level was the number of people who could be heard simultaneously. Personnel working at centers with a more open design reported significantly more health problems and disadvantages (Truchon-Gagnon & Hetu, 1988). In a Danish study (BUPL, 1998), more than half of the studied day nurseries for children aged 0-3 years showed LAeq,8h-levels exceeding 80 dB (acoustic measurements in one room per daycare center) and up to 7% exceeded 85 dB. For kindergartens with children aged 3-6 years, more than 73% showed LAeq,8h-levels exceeding 80 dB and about 17% exceeded 85 dB.
Several adverse health effects in personnel and children in daycare centers have been reported including hearing impairment, sleep disturbances, stress-related somatic effects, and cognitive effects, e.g., on reading, long-term memory, and learning (Haines, Stansfeld, Job, & Berglund, 1998; Maxwell & Evans, 2000), and voice problems (Bistrup, 2001). Reduced noise levels may improve hearing, understanding, and communication as well as the stress hormone levels, which can lead to improved quality of life in daycare centers, both in children and personnel.
Materials and Methods
Our basic study comprised 373 subjects employed at 29 daycare centers, randomly selected from approximately 50 daycare centers in the city of Lund and its surroundings in southern Sweden. Half of the centers were in urban areas and the other half were in suburbs. Each daycare center consisted of one to three departments with standard furniture and standard equipment. Each department had approximately 18-20 children in the age group 1-6 years. The playing room in each daycare center had a room volume of approximately 100 [m.sup.3]/center.
All participants completed a questionnaire with validated questions about noise disturbances, illumination problems, symptoms related to the indoor climate, and work-related hearing problems (Astolfi & Pellerey 2008; Landstrom, Lofstedt, Akerlund, Kjellberg, & Widen, 1990; Lundquist, Holmberg, & Landstrom, 2000; Rudblad, Andersson, Stridh, Bodin, & Juto, 2002). The noise questions covered the perceived disturbance level; the noise-generating sources in the playrooms (e.g., children, ventilation system, outdoor noise, furniture) and dining rooms (e.g., children, ventilation system, outdoor noise, noise from kitchen, cutlery, and furniture); the need to plan the daily activities to reduce the noise levels (five alternatives: never to very often); and the need for silence after finishing work (five alternatives: never to very often). A visual analogue scale (VAS; 10 cm) was used to estimate the perceived noise disturbance level (Landstrom et al., 1990; Lundquist, Holmberg, & Landstrom, 2000; Wewers & Lowe, 1990). The response rate was >95% as the questionnaires were delivered and collected by the head of the department at each daycare center.
In five of these daycare centers, the personnel (N = 81) had for several years complained about different types of noise problems. These centers were all based on a module system and were quickly built up within approximately a three-month period. After a thorough investigation of the working environment in these centers, acoustical treatment of the dining and playrooms was undertaken with a combination of a suspended absorbent ceiling and wall-mounted absorbers on two adjacent walls. The absorbers were 4-cm-thick glass and wool products attached directly to the ceiling. The wall-mounted absorbers had a protective glass fiber covering preventing mechanical damage.
Six months after the acoustical treatment, the personnel at these daycare centers completed the same questionnaire for a second time (n = 68). Basic (empty rooms) and normal activity measurements including background noise and reverberation time were performed using fixed microphone positions both before and after the acoustical treatment. The results of the acoustical treatment effects have been reported in detail elsewhere (Nilsson & Gerhardsson, in press).
The microphones were attached to the walls. A calibration procedure was undertaken in such a way that the A-weighted SPLs measured by the microphones attached to the walls corresponded to the SPLs averaged over the floor area at levels that corresponded to the heights of the personnel and the children (Nilsson & Gerhardsson, in press). This was achieved by simultaneously measuring the SPLs at the wall positions and the SPLs out in the room at several microphone and loudspeaker positions. The loudspeaker was emitting broadband noise at a constant sound power level into the room. Thus, a difference between the wall and the room average SPL was established. In our study, the difference between the values measured at the wall positions and the room averages were about 1 to 2 dB (Nilsson & Gerhardsson, in press).
Parametric statistical methods were used for the variables that were approximately normally distributed (Student's t-test). Most variables, however, showed a skewed distribution, and for these, nonparametric statistical processing was applied (Mann-Whitney U-test). Nonparametric correlation coefficients were calculated (Spearman's rho). We regarded p-values < .05 as statistically significant. Calculations were performed using SPSS v. 18.0.
Background and questionnaire data from the total material and from the five centers before and after acoustical treatment are presented in Table 1. More than 95% of the personnel were females. The median employment time at daycare centers was approximately 20 years and full-time employment was equal to eight working hours per day (40 hours/week). The median employment time at the current daycare center was about 10 years. From April to September the personnel spent 40%-50% of their working time outdoors. The corresponding outdoor working time from October to March was about 20%-25%. Around one-fifth of the personnel were active smokers.
Before acoustical treatment at the five centers, the personnel (N = 81) found the perceived noise disturbance level in the playing rooms rather disturbing (5.2 cm; range = 0.4-8.5; VAS scale). About 70% of the personnel stated that the children were the dominant noise source in the playing rooms. Talking and shouting among the children were the most disturbing activities, followed by noise from the children's playing and from their handling of building blocks (Table 1). Similar figures for the children's talk and shouts were also found in the dining rooms. About 39% of the staff often or very often regularly planned outdoor activities to reduce the noise levels. More than 40% of the personnel often or very often had a need for silence when they arrived at home after work.
After the acoustical treatment at the five daycare centers (n = 68), the median noise disturbance level slightly (nonsignificantly) decreased to 5.0 cm (range = 0-8.3 cm) in the playrooms. The most disturbing noise sources in the playrooms and dining rooms still came from the talking and shouting of the children (Table 1; nonsignificant change). After the acoustical treatment, the proportion of the staff who often or very often planned outdoor activities to keep down the noise level showed a nonsignificant decrease from 39% to 25%. The proportion that often or very often felt a need for silence after work had decreased (nonsignificantly) from 42% to 37%.
As the staff mainly consisted of females, well-known noise sources such as a sewing machine and a hair drying machine were used for comparison with the noise levels in the playing rooms before the acoustical treatment. The noise from a sewing machine (median = 2.2 cm; range = 0-6.5) and from a hair drying machine (median = 3.3 cm; range = 0-8.3) was considerably less disturbing as compared with the perceived noise level in the playing rooms (median = 5.2 cm; range = 0.4-8.5) at the five centers. The nonparametric correlation between the perceived noise levels from the sewing machine and from the hair drying machine was strong ([r.sub.s] = .81; p < .001). None of them correlated significantly (Spearman), however, with the perceived noise level in the playing rooms.
Before the acoustical treatment, about 10% of the staff complained about work-related hoarseness and throat irritation. About 42% indicated a hearing deficiency that they related to the working environment. Around 32% stated that they had a hearing deficit that was established by a physician. After the acoustical treatment about 16% of the staff complained about work-related hoarseness and 12% of throat irritation.
The results of the technical noise measurements before and after the acoustical treatment at the five centers have been reported elsewhere (Nilsson & Gerhardsson, in press). In summary, baseline measurements that were performed in the dining and playrooms without any children or personnel present showed background sound levels between 30-41 dB(A) and 51-54 dB(C), reverberation times between 0.4 and 0.7 seconds, and activity sound levels between 68 and 79 dB(A). After the acoustical treatment the SPLs were reduced by 2 to 6 dB in the playing rooms and by 0 to 3 dB in the dining rooms. The reverberation time was reduced by 20% to 50% (Nilsson & Gerhardsson, in press).
Our study focused on personnel at five Swedish daycare centers with reported acoustical problems. These buildings were all based on a module system, and were all built up within approximately a three-month period. At baseline, the personnel found the noise level rather disturbing with background sound levels between 30-41 dB(A-weighted) and 51-54 dB(C-weighted), reverberation times between 0.4 and 0.7 seconds, and activity sound levels between 68 and 79 dB(A-weighted). Both the acoustical measurements and the questionnaire data indicated that talk and shouts from the children were the dominant noise sources. These noise sources were considerably more disturbing as compared with the noise from commonly used devices such as hair dryers and sewing machines. During the last decade, the group sizes at Swedish daycare centers have increased, in some cases from about 15 to 20-22 children, giving more subjects and noise per room and square meter area. Often the building and the ventilation system, however, are unchanged.
Children's voices generally have a higher frequency, and the sharp pitch sound can be more annoying than the deeper voices of adults. Usually, the noise annoyance increases with the sound level (Kryter, 1985), the tonal character of the noise, and the variability of the exposure (Holmberg, 1997). After the acoustical treatment, the SPLs were reduced by 2 to 6 dB in the playrooms in our study. Corresponding figures in the dining rooms were 0 to 3 dB. The reverberation time was reduced by 20% to 50% (Nilsson & Gerhardsson, in press). At follow-up, about six months after the acoustical treatment, the perceived noise disturbance level in the playing rooms had slightly but not significantly decreased. This is in accordance with previous studies (Landstrom et al., 1990; Lundquist et al., 2000; Wewers, & Lowe, 1990), showing rather weak relationships between the sound level and the perceived annoyance level. In one study (Guski, 1999) about one-third of the annoyance reactions were explained by the variance in acoustic features, and another third by the variance in personal and social variables.
Positive effects were, however, observed both on the perceived need to plan the daily activities (e.g., by dividing the children into an indoor and outdoor group) to keep down the noise disturbance level, and on the perceived need for silence when arriving at home after work (Table 1).
Low frequency ventilation sounds mainly originate from fans and the air turbulence, which is generated inside ducts and around air supplies and exhausts. Even if the porous absorbers that were attached to the ceilings and walls of the playing and dining rooms in our study were not primarily designed to reduce the noise from the ventilation system, we still observed a background noise level reduction of 1 to 2 dB. Other low frequency sounds in our investigation originated from footsteps on floors, e.g., in corridors, which can be quite disturbing, almost giving an echo effect in this type of module-built daycare center. The latter noise can be more difficult and more expensive to counteract.
To reach a statistically significant improvement of the noise situation at work, the activity levels will probably need to be reduced by about 6-7 dB(A-weighted) (Bistrup, 2002; Nilsson & Gerhardsson, in press). The Munich Airport study indicates that a reduction with about 10 dB(A-weighted) during a one-year period is needed to show positive effects on noise-induced cognitive impairment in children (Bistrup, 2002; Hygge, Evans, & Bullinger, 2002). Similarly, studies suggest that interventions to reduce the noise levels in classrooms of school children are likely to lead to improved performance (Hygge et al., 2002). These studies are, however, all limited by the fact that they compared the performance of different cohorts of children attending the same school.
Technical preventive measures can reduce the sounds reverberating from ceilings and walls but not the direct mouth-to-ear sound. The latter sound can only be reduced by the child itself, e.g., by creating an atmosphere that allows a person to talk less loudly. These preventive steps are quite inexpensive, and even if the noise reduction of each step may not look too impressive the summation effect of all preventive measures undertaken may add up to 6-7 dB(A-weighted), a level that is probably needed to reverse the adverse health effects reported in children and personnel at daycare centers (Bistrup, 2002; Nilsson & Gerhardsson, in press).
In summary, the acoustical treatments in these five daycare centers reduced the SPLs by 2 to 6 dB in the playing rooms and by 0 to 3 dB in the dining rooms.
A considerable improvement of the reverberation time was observed, which was decreased by 20% to 50%. The perceived noise annoyance level among the personnel was slightly but not significantly reduced. This finding is in accordance with other reports showing a weak association between the sound level and the perceived annoyance level. It seems probable that a reduction of the sound level by 6 dB or more is needed before the study subjects can feel a significant subjective improvement of the noise situation at work.
Although most of the information presented in the Journal refers to situations within the United States, environmental health and protection know no boundaries. The Journal periodically runs International Perspectives to ensure that issues relevant to our international membership, representing over 20 countries worldwide, are addressed. Our goal is to raise diverse issues of interest to all our readers, irrespective of origin.
Acknowledgements: The authors gratefully acknowledge AFA Insurance for their financial support and Saint-Gobain Ecophon for providing and mounting the absorbing material. The study was conducted in accordance with national and institutional guidelines for the protection of human subjects. The study was approved by the Ethical Committee of Lund University, Sweden.
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Lars Gerhardsson, MD
Occupational and Environmental Medicine
Sahlgrenska Academy and University Hospital
Saint-Gobain Ecophon AB
Corresponding Author: Lars Gerhardsson, Occupational and Environmental Medicine, Sahlgrenska Academy and University Hospital, Box 414, SE-405 30, Gothenburg, Sweden. E-mail: firstname.lastname@example.org.
TABLE 1 Background Factors and Questionnaire Data From the Total Material and From the Five Selected Centers Before and After Acoustical treatment Variables Total Material (a) Number of subjects 373; 364 females Age (years) 45 (19-64) Employment time 20 (0-43) (years) Employment at current 10 (0-34) daycare center % of working time 45 (0-100) outdoors, Apr.-Sept. % of working time 25 (0-85) outdoors, Oct.-Mar. Active smokers 16% Ex-smokers 26% Perceived noise 5.4 cm (0-10) disturbance level Most disturbing noise Children 75% sources in playing Ventilation system 7% rooms Other sources 4% Most disturbing Talking, shouting 74% children activities Playing 9% in playing rooms Building blocks 7% Most disturbing noise Children 72% sources in dining Cutlery 11% rooms Ventilation system 3% Planned outdoor Sometimes 27% activities to reduce Often 31% noise levels Very often 15% Need for silence Sometimes 34% after work Often 31% Very often 23% Variables Centers Before Acoustical Treatment (a) Number of subjects 81; 78 females Age (years) 45 (21-64) Employment time 20 (0-39) (years) Employment at current 10 (0-31) daycare center % of working time 40 (0-75) outdoors, Apr.-Sept. % of working time 21 (0-50) outdoors, Oct.-Mar. Active smokers 24% Ex-smokers 31% Perceived noise 5.2 cm (0.4-8.5) disturbance level Most disturbing noise Children 69% sources in playing Ventilation system 12% rooms Other sources 9% Most disturbing Talking, shouting 58% children activities Playing 20% in playing rooms Building blocks 15% Most disturbing noise Children 70% sources in dining Cutlery 12% rooms Ventilation system 4% Planned outdoor Sometimes 26% activities to reduce Often 32% noise levels Very often 7% Need for silence Sometimes 47% after work Often 22% Very often 20% Variables Centers After Acoustical Treatment (a) Number of subjects 68; 65 females Age (years) 47 (22-62) Employment time 20 (1-40) (years) Employment at current 13 (1-32) daycare center % of working time 50 (0-80) outdoors, Apr.-Sept. % of working time 20 (0-75) outdoors, Oct.-Mar. Active smokers 21% Ex-smokers 32% Perceived noise 5.0 cm (0-8.3) disturbance level Most disturbing noise Children 60% sources in playing Ventilation system 9% rooms Chairs 4% Most disturbing Talking, shouting 60% children activities Playing 15% in playing rooms Building blocks 4% Most disturbing noise Children 65% sources in dining Cutlery 3% rooms Chairs 3% Planned outdoor Sometimes 31% activities to reduce Often 21% noise levels Very often 4% Need for silence Sometimes 35% after work Often 21% Very often 16% (a) Values are median values and ranges or fraction/ percentage.
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|Title Annotation:||INTERNATIONAL PERSPECTIVES|
|Author:||Gerhardsson, Lars; Nilsson, Erling|
|Publication:||Journal of Environmental Health|
|Date:||Mar 1, 2013|
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