Jack Hammer Research Articles

An Assessment of Drilling and Blasting Techniques at Granite Quarry of AFDIN Construction Company Limited, Katsina State, Nigeria

This research work assessed the Drilling and Blasting Techniques at the Granite Quarry of AFDIN Construction Company Limited, Katsina State, Nigeria. The objectives were to identify drilling and blasting equipment, find out the drilling pattern and parameters, assess blasting method and its compliance with safety practices in and around the blast site and review the impact of the blasting operations on the surrounding environment. As an introduction, the concept of drilling and blasting activities and how they affect immediate environment were explained. The study assessed quarry activities using field visit and interviews. Equipment identified at the quarry were Wagon drill, Jack hammer, Compressors, Rock breaker, Excavators and tippers, etc. Also, Atlas Copco YT27 Jack Hammer was the main tool for hole drilling with either Square or Rectangular drilling pattern being adopted and Drilling dimensions of 4x5ft or 4x4ft (spacing and burden) were frequently used at the Quarry. Hole depths used were 6ft, 8ft, 10ft, and 12ft and drilling bit of 1-inch or 2-inch. Furthermore, the study identified that, 2,088.95 kg of explosives (10% High Explosive and 90% Low Explosive) was used to charge 2000 drilled holes with an average hole depth of 3.65metres and diameter of 32mm. A total of 7,394 tonnes of granite rock was blasted. Result from immediate blasting at the quarry indicated presence of dust and fumes within the quarry environment and nearby villages, inhalation of which could lead to serious occupational hazards. Conclusively, the explosion sound from blasting and fly-rock fragments have some serious environmental and health effects to both workers and neighbouring communities in terms of noise pollution and vibration to structures. Wetting the environment and crushing process was recommended to minimise dust generation to barest minimum to protect workers from occupational diseases such as silicosis and Pneumoconiosis, also wearing of personal protective equipment, electric blasting method, corporate social responsibilities to the communities were recommended.

Treatment with nano-silica and bacteria to restore the reduced bond strength between concrete and repair mortar caused by aggressive removal techniques

Removal of degraded concrete during repair activities might have a detrimental impact on the bond strength between the concrete and the repair mortar. This research aims to improve the bonding strength in case aggressive removal techniques were used, by the singular and combined application of bacterially induced CaCO3 and colloidal nano-silica (CNS) treatments. Water jetting (WJ) and jackhammering (JH) were compared and the treatments were performed on the substrates prepared with the technique causing the lowest bonding. Pull-off test results on crushed stone concrete (CC) substrates showed that JH substrates possessed the lowest bond strength compared to WJ and unprepared substrates. To assure that reported results are reproducible, pull-off tests were also performed on another type of concrete, gravel concrete (GC). The results showed that in both cases JH-substrates achieved a lower bond strength than unprepared- and WJ-substrates. The reduced bond strength by JH was restored by the CNS treatment irrespective of the concrete composition. Regarding the biodeposition treatment, the spraying technique showed to be superior to the pouring technique. Microstructural analysis confirmed the survival of the bacteria and carbonate precipitation. Porosity of the prepared substrate surfaces was studied by capillary absorption, water absorption (including the gravity effect) and vacuum absorption tests. The reduction in the initial water uptake of CNS-treated samples was evidenced by the precipitation of the silica gel at the superficial layer of the substrate. The efficacy of Energy Dispersive X-Ray Analysis (EDX) to recognize the interlayer of layered composites with a monolithic structure was observed.

Ground vibration generated by hydraulic rock breakers and its impact on the safety of nearby earthfill dam in a graphite mine

A detailed impact analysis on the effects of non-explosive chemicals and hydraulic rock breakers at a graphite mine in India close to an irrigation dam was carried out in this study. The dam was 70 m from the mining lease boundary. When a single hydraulic rock breaker worked on fractured rock mass, the magnitude of ground vibration recorded at 10 m on the same working bench was 2.37 mm s −1 but when it worked on fresh rock surface the ground vibration at 9 m on the same working bench was 4.67 mm s −1 . Beyond 35 m on the same bench, no ground vibrations were recorded. Ground vibrations generated by three jack hammer drilling machines operating simultaneously on the same working bench were less than 0.5 mm s −1 when measured at 7.2 m distance. The combined effect on the magnitudes of ground vibrations by two hydraulic rock breakers operating simultaneously on the same bench 6 m apart was found to be negligible. The ground vibrations generated by hydraulic rock breakers and other mining activities were found to be lower than required to cause any structural damage or threat to the stability of the dam.

Monitoring, profiling and classification of urban environmental noise using sound characteristics and the KNN algorithm

Environmental noise is a key factor affecting the quality of life in modern societies as they influence an extended set of human activities. Unwanted sounds, typically characterized as noise, can be of many types and vary in their impact and the ways to be confronted on behalf of competent public authorities. In this work, we describe environmental noise in a qualitative manner using sound-specific features from the time and spectral domains. These features consist of 8 temporal (including RMS, standard deviation, Zero Crossing Rate), 11 spectral (including spectral envelope slope, skewness, spectrum mass center, peak amplitude crest, spread and skewness) and 4 perceptual (including Mel Frequency Cepstral Coefficients) descriptors. Based upon a set of 8 discriminant types of unwanted sounds, typically met in urban environments (car horn, children playing, dog barking, drilling, engine idling, jack hammer, siren and street music), we specify a methodology of matching environmental noise into these categories. Using training and test data from the UrbanSound8K public dataset, we use the K-Nearest Neighbors (KNN) algorithm for classification. The algorithm has been configured to allow from 1 to 3 neighbors, while three distance metrics (Euclidean, Chebyshev and cosine) have been employed to create 9 models that achieve performance between 70% and 85%.

Bond strength between concrete and repair mortar and its relation with concrete removal techniques and substrate composition

This study investigates how concrete removal techniques affect substrates of different compositions, and as a result, the bonding with repair mortar. To this end, substrate surfaces of different concrete compositions, micro-concrete (MC), gravel concrete (GC) and crushed stone concrete (CC), were treated by using three commonly used removal techniques; hydrodemolition/water-jetting (WJ), jack-hammering (JH) and grit blasting (GB). Automated laser measurements (ALM) and the volumetric sand patch technique were employed to determine the surface roughness of the substrates. The effect of the substrates parameters such as aggregate size and uniformity on the bonding and failure modes was investigated. Uniformity of the substrates was evaluated by porosity measurements. According to the results, bond strength, surface tensile strength, failure modes and surface roughness were dependent on the aggregate size, aggregate shape and uniformity of mixture. The largest aggregate size and highest porosity along with the highest microcrack density and roughness belonged to CC mixtures. A high correlation was observed between the measured water transport and bond strength of samples. Micro-cracking and a weak interfacial transition zone (ITZ) seem to be the detrimental factors influencing the bond strength of samples treated with JH and WJ, respectively. The influence of WJ on the bond strength was dependent on the mix composition parameters such as aggregate size.

A case of avascular necrosis of capitate bone in an air compressor jack hammer worker

Introduction: Avascular necrosis (AVN) is very rare in capitate bone. It mostly occurs due to direct trauma to wrist. However, it could also occur as the result of disturbed blood supply due to repetitive micro-trauma in rare cases. Case Report: In this report, a 30-year-old man who was an air compressor jack hammer worker with chronic wrist pain was presented. Imaging revealed a low-signal intensity lesion on T1-weighted which supported AVN of capitate. Blood supply damage was due to continuous stress to palmar hand as the consequence of working with air compressor jack hammer which led to AVN of capitate. Conclusion: AVN of capitate could occur as the result of repetitive micro-trauma. It has a high correlation with the job of patients. Radiography does not help in the first stages. Magnetic resonance imaging (MRI) has high diagnostic sensitivity. In the primary stages in patients with occupation-induced AVN, it could be improved by changing the job and temporary immobilization.

How concrete removal techniques affect the bonding between concrete and repair mortar

Many bonding failures between the substrate and repair mortar are attributed to too aggressive removal of the contaminated concrete and incorrect use of repair materials. To this end, in this study the effect of concrete removal techniques on substrates of different compositions and, as a result, on the bonding with repair mortar has been investigated. Substrate surfaces of different concrete compositions, micro-concrete (MC) and crushed stone concrete (CC), were treated by using three commonly used techniques: grit blasting (GB), jack-hammering (JH), and hydrodemolition/water-jetting (WJ). Automated Laser Measurements (ALM), sand patch tests and surface tensile strength measurements were applied to characterize the substrate surface. According to the results, the co-lateral effects of removal techniques such as WJ are dependent on the concrete mix composition. Moreover, WJ- and JH- treated samples achieved a lower surface tensile strength and bond strength compared to GB-treated slabs.

Seismic performance of repaired lightly-reinforced concrete walls

As a result of the 2010-2011 Canterbury earthquakes, over 60% of the concrete buildings in the Christchurch Central Business District have been demolished. This experience has highlighted the need to provide guidance on the residual capacity and repairability of earthquake-damaged concrete buildings. As limited testing has been performed on repaired components, this study focuses on the performance of severely-damaged lightly-reinforced concrete walls repaired through replacement of reinforcement and concrete in the damaged region. The damage prior to repair included buckling and fracture of longitudinal reinforcement, crushing and spalling of concrete, and, for one of the two specimens, out-of-plane instability of the gross section. Prior to repairing the wall specimens, tensile testing of reinforcement with welded connections was conducted to verify acceptable performance of welds suitable for reinstating the damaged reinforcement. Repairs to the specimens consisted of removal of damaged concrete through either hydro-demolition or jack hammering, followed by cutting and removal of damaged reinforcement and reinstatement of new reinforcement and repair mortar. The two repaired wall specimens were tested using a standard protocol that was identical to that used for one of the two original wall specimens. Aside from a difference in the elastic stiffness, the load-deformation responses of the repaired specimens were similar to that of the originally-tested specimen through to the first loading cycle at 2.0% drift, beyond which strength degradation was more pronounced for the repaired specimens. The overall performance of the repaired walls relative to the original wall indicates that it is feasible to achieve acceptable performance of severely-damaged concrete walls repaired through replacement of reinforcement and concrete in the damaged region.

Estimation of Sound Level Produced During Drilling of Igneous Rock Samples Using a Portable Drill Set-up

The mechanical strength of rock is one of the most important factors of concern to engineers involved in mining operations. Information about rock strength is used in rock excavation planning and design operations in civil and mining engineering. Drilling is widely carried out in hard rocks for blasting the rock mass so that the blasted material can be easily loaded by the excavators. The drillability of rock depends on many factors including rock properties whereas properties such as compressive strength, porosity, density etc. are uncontrollable parameters during drilling process. A number of studies have been reported recently on the application of sound level which have been concentrated on using either CNC or jack hammer machine for drilling purpose. It is worth mentioning that neither CNC machine nor jack hammer drill set-up is the normal way of drilling in rock, nor in mining, civil or any other operations, not even in working with rock in installation of countertops. Therefore, it is difficult to exactly say whether the noise generated during drilling is only from the rock drilling or from the drilling unit itself. In view of the above, it is important to fabricate a new drilling set-up which is a silent unit in itself. Such unit when used for drilling purpose will clearly indicate the change in sound level produced with different rock properties.

Study on Noise Levels Generated due to Jack Hammer Drills in Granite Quarries

In this study, environmental noise and operator noise dose generated by jack hammer drilling were monitored in seven granite quarries in South India. The ambient noise was monitored at different distances and directions from the source. The maximum noise level was found in the downwind direction. The correlation study between distance and noise level was carried out to determine the safe zone limit for each quarry. To know the combined influence of compressive strength, rock density and distance, multiple regression analysis of data was conducted and a model was developed for the prediction of noise levels. Model adequacy was checked using F-statistics, normal distribution curve and correlation between predicted and measured values of noise levels. The operator noise dose in each quarry exceeded the prescribed limit. However, it can be controlled by providing ear plugs/ear muffs and by properly maintaining the jack hammers.

Blast-Induced Ground Vibration Damage Assessment for Foundation Work at a Thermal Power Project in India

This paper presents the extensive trial blasts conducted for damage assessment due to blast-induced ground vibrations for removal of hard rocks as well as establishment of safe blasting zones during excavation work at a proposed thermal power project in India. During the excavation work it was feared that the impact of blasting may cause damage to the rocks or extension of cracks to the nearby foundations/foundation bases for various types of sensitive structures. A number of trial blasts with varying designs and charging patterns were carried out at the site. The impact of ground vibration waves were assessed on nearby structures/foundations. Ground vibrations were monitored at varying distances in a straight line, to find out the characteristics of wave propagation in the particular medium. Based on the analyses of recorded vibration data, it was suggested that no blasting should be carried out within 5 m when the foundation work is in progress. Within 5–15 m, controlled blasting should be carried out with 32 mm diameter Jack Hammer Drilling Machine while beyond 15 m and up to 25 m, 100 mm diameter drill machine can be used with hole depths up to 3.0 m. Within the zone of 25 m to 35 m from the foundation, the depth of blastholes may be more than 3.0 m but it should not be greater than 4.5 m. Beyond 35 m zone, the depth of blast holes should be between 4.5–6.0 m. It was also suggested that a clearance of at least 0.5 m from both the edges of the blasting face should be used between the boundary of excavation line and the last row of holes to minimize over break beyond the excavation line. Lighter explosive charges with longer delay periods should be used for the blastholes adjacent to the excavation boundary.

UP-03.081 Transureteral Ureterolithotripsy of Ureteral Calculi: Which Is Best, Pneumatic or Holmium Laser Technique?

Urinary calculi are important problem in urology. Ureteral stones can cause obstructive uropathy and subsequent deterioration of renal function. Extracorporeal shockwave lithotripsy (SWL) and rigid and flexible ureteroscopy have greatly improved the urologist's ability to treat ureteral calculi. However, the success rate of SWL for impacted ureteral calculi is reportedly low. For stone fragmentation, a variety of lithotripters can be used, including ultrasonic, electrohydraulic, pneumatic and laser lithotriptors. Pneumatic lithotripsy and holmium:YAG lithotripsy have reported favorable outcomes. The Swiss Lithoclast developed in Lausanne, Switzerland, fragments the stones by oscillary movements of metal probe against the stones like a jack hammer. The thermal effect produced by holmium:YAG laser pulses are due to formation of plasma bubble. This bubble at the tip of the fiber connected to the holmium:YAG laser makes it possible to work on stones and soft tissues. Our aim was compare two types of lithotripter: holmium: YAG laser and pneumatic one in transurethral ureterolithotripsy (TUL) for management of ureteral calculi ≥1cm.

A Study of FRP–Concrete Bond under Impact

Our understanding of how the bond between FRP and concrete performs under impact loading is severely limited. In this paper, bond performance of Sprayed FRP with concrete was studied under impact loading. A novel 550 mm × 150 mm × 150 mm notched specimen was developed and a 75 mm wide strip of Sprayed FRP was applied to strengthen the specimen. A novel test set-up designed to minimize the influence of specimen rebound after impact as well as eliminate the need to correct the load data for inertial effects was developed. FRP strains were measured using strain gauges carefully installed on the FRP, and the bond stress was calculated using the differential strain values. A kinematics analysis was also performed to translate the vertical deflections into strain values. Three types of surface preparation methods (water jetting, sand blasting, and jack hammering) were studied. Specimens are tested under four different strain rates (four different hammer heights of 250, 500, 750, and 1000 m) and the results were compared with quasi static values using loading rates of 0.005, 0.05, and 0.5 mm/min. Results showed that sand blasting is the most effective surface preparation method resulting in the highest bond strength values. Impact results were characterized using a Dynamic Improvement Factor (DIF). Results indicate that the FRP–concrete bond is highly strain sensitive, and in general the bond strength increases and the fracture energy decreases under higher rates of strain. Untreated specimens are shown to be more strain-rate sensitive than the surface treated ones.

Zur Beziehung zwischen Verbund Qualität und Impact-Echo Frequenzspektrum / On the Relation between Bond Quality and Impact-echo Frequency Spectrum

According to EN 1504-10 and ACI Concrete Repair Manual, bond strength and interface quality are the main features of repair system necessary to be assessed. Pull-off test is most commonly used for bond strength evaluation but growing interest in nondestructive techniques (NDT) is recently noted. Impact-echo (IE) is treated as the most promising one for this purpose. The aim of this paper is to analyze an effect of bond quality on stress wave propagation in repair systems. A group of samples has been prepared in order to obtain repair systems of different bond quality. Prior to repair, quality of concrete substrates has been characterized according different techniques: compressive strength, superficial cohesion, surface roughness index and cracking quantification. Than a polymer-modified repair mortar has been applied. After hardening, IE signals have been recorded and pull-off bond strength determined. The relationships between parameters characterizing surface quality, bond strength, IE frequency spectrum and results of wavelet analysis of IE signal have been analyzed. 2 ICPIC 2010 – 13 International Congress on Polymers in Concrete Table 1: Characteristic of tested repair systems Group A Group B Concrete substrate C30 C40 C45 C25 C35 C50 Compressive strength classes C30/37 C40/50 C45/55 C25/30 C35/45 C50/60 Surface preparation PL, SB-D, JH, HD NT, SB-W, SC, LC Sample dimensions 80x60x10 cm 50x50x7cm Repair material PCC (A), Dmax = 2,0mm PCC (B), Dmax = 0,25mm Repair layer thickness 3cm 3cm 2.2 Results of substrate characteristics The quality of substrates was characterized from point of view of their roughness, microcracking and surface tensile strength. The roughness was measured by sand patch test according to EN 1766 resulting Surface Rough Index SRI (Fig.1a). Substrates of Group A can be ranked from polished smooth surface (PL), by dry sandblasted (SB-D) and jack hammered (JH) to very irregular hydrodemolitioned one (HD). In Group B low-pressure waterjetting (LC) has no big influence on profile in comparison to brushed surface (NT), while wet sandblasting (SB-W) and scarification (SC) increase roughness a little. Microcracking of samples of Group A was observed on the cross-section of the 8 cm cores on the near-to-surface layer in the area of 2 cm depth. Density of microcracks was calculated (Fig.1b). It can be concluded, that more aggressive surface preparation technique influence more on microcracking: it was observed two times higher density of microcracks after jack hammering (JH) and hydrodemolition (HD) than after dry sandblasting (SB-D) and polishing (PL). As the aggressiveness of surface treatment of samples of Group B was small, the microcracking was not observed here, although it can be expected a little higher level for scarification. a) 0.0 1.0 2.0 3.0 4.0 5.0 P L SB -D JH H D L C N T SB -W S C surface treatment SR I [m m ] Group A Group B b) Group A 0.00 0.01 0.02 0.03 0.04 0.05 P L SB -D JH H D surface treatment L A [ m m /m m 2 ] Figure 1: Surface Roughness Index, SRI (a) and density of microcracks, LA (b) depending on the method of surface treatment The pull-off test according EN 1542 and ASTM C 1583 04 commonly used for evaluation of bond strength (Fig.2b) was applied for surface tensile strength (fhs) measurement (Fig.2a) including type of failure registration. In case of samples of Group A the concrete quality did not have a major influence on the surface tensile strength after surface treatment as it was for samples of Group B (Fig.3). It can be also observed (Fig.4) that for surfaces jack hammered (Group A) and scarified (Group B), more that 50 % of failures appeared near in the superficial zone (type A1, see Fig.2a). It is probably due to microcracking already mentioned. a) b) A A /B B 15 mm repair material concrete substrate Figure 2: Pull-off for evaluation of surface tensile strength (a) and bond strength (b) A1 A2 A3 15 mm T. Piotrowski, A. Garbacz, A. van der Wiellen, L. Courard, F. Nguyen 3

Proactive regulation engenders creative innovation: Quieting the jack hammer.

In 2002, the New York City Department of Environmental Protection undertook to completely revise the city’s Noise Code; it went into effect in 2007. The Mayor’s Office made the reduction in construction noise a priority. Incentives were provided for the application of best management practices and the use of quieter equipment. DEP staff proposed the development of a remediation strategy for pneumatic pavement breakers. Working with KeySpan Energy (now National Grid), they approached Zo‐Air Company, an industrial tool distributor, who developed the “No Racket Jacket.” The key to developing a successful engineered solution is understanding the noise source. Most of the noise emissions from a pavement breaker come from internal components, not the tool bit hitting the pavement. Enclosing the source significantly reduces the noise emissions. The jacket al.so serves to insulate the operator from the exhaust air of pneumatic units, and the oil often spewed onto their legs. This paper discusses the development process which included four prototypes, and the results, with data from source sound level measurements and operator dosimetry. Three scenarios were tested: unremediated pneumatic hammer, pneumatic hammer with the “No Racket Jacket,” and an electric pavement breaker.

An experimental investigation of jack hammer drill noise with special emphasis on drilling in rocks of different compressive strengths

An attempt has been made in this paper to investigate the influence on sound level due to drilling in rocks of varying physical properties i.e. compressive strength and abrasivity using jackhammer drill. For this purpose, a jackhammer drill setup was fabricated wherein the thrust applied can be varied while drilling vertical holes. The compressive strength and the abrasivity of various rock samples collected from the field were determined in the laboratory. A set of test conditions were defined for measurement of sound level of the jackhammer drill.Also, with the help of the experimental setup, vertical drilling was carried out on the rock samples for varying thrust and air pressure values and the corresponding A-weighted equivalent continuous sound levels were measured.The results of this study indicate that, increase in thrust increases the sound level at higher midband frequencies in the noise spectrum. The study indicated the sound level near the drill rod to be 0.5 to 1.5 dB, 2.0 to 3.0 dB and 4.0 to 6.0 dB higher relative to that at the drill bit, the exhaust and the operator’s position respectively at an air pressure of 5 kg/cm 2 and 160 N thrust for all the rock samples tested. Both the thrust and air pressure were found to have a significant effect on the sound level produced by jackhammer drill at all the measurement locations. The study further shows that an increase in sound level of the order of 1.5 to 2.5 dB at the operator’s position can occur with an increase in air pressure by 2 kg/cm 2 at 160 N thrust and with an increase in compressive strength and decrease in abrasivity of rocks. Also, the increase in sound level at the operator’s position with increase in compressive strength and decrease in abrasivity of rock is of the order of 1.0 to 2.0 dB. In order to maintain a constant penetration rate in the rocks, both the thrust and air pressure need to be increased with an increase in compressive strength and decrease in rock abrasivity.Therefore,increased compressive strength and lower abrasivity of rocks will require higher air pressure and thrusts to be applied to achieve an optimum penetration rate and therefore will result in higher sound level at the operator’s position and at other measurement locations. © 2007 Institute of Noise Control Engineering.

Phaco Transducers: Basic Principles and Corneal Thermal Injury

OBJECTIVE:To document the clinical circumstances of a thermal burn of a cornea created during a technically flawed phaco procedure, and to review the basic physics of the mechanical forces that phaco transducers generate to emulsify cataract. STUDY DESIGN: A case history review of a thermal burn plus an engineering library review of the dynamics of ultrasonic acoustic activity in fluids. RESULTS: The mechanical forces that emulsify cataract are shock and fluid waves generated when transient micron-sized bubbles implode within a few acoustic cycles rather than a jack hammer effect of the movement of the phaco tip. CONCLUSIONS: An understanding of the basic dynamics of phaco energy within the eye will aid surgeons to better manage the mechanical energy and heat present. Finally, it may generate more efficient phaco devices that are less likely to damage eye tissue.

Hand-Arm Vibration Syndrome in a Group of U.S. Uranium Miners Exposed to Hand-Arm Vibration

Abstract Medical evaluations were conducted in New Mexico on 134 uranium mine workers. Ninety-one of these workers were miners who used jack-leg-type drills on their job at the time of the survey. Engineering evaluations of two jack-leg-type drills and a jack hammer were carried out while four of the miners operated the tools. The medical evaluations were designed to diagnose Hand-Arm Vibration Syndrome from use of these vibrating pneumatic hand tools. Among 49 miners, selected for the absence of confounding exposures or medical conditions, 17 percent were in the vascular stages of Hand-Arm Vibration Syndrome and 24 percent in the neurologic stages according to the Taylor-Pelmear Classification System. The median latency of tingling, numbness, and blanching was the same, 4.5 years. Unweighted vibration acceleration levels measured on three pneumatic tools (a small and large jack-leg-type drill and a small jack hammer) ranged from 5.16 to 19.04 g(rms) (corresponding to 50.62–186.78 m/sec/sec) in the axial ...

Shock wave processing apparatus

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Loudness (or annoyance) summation of combined community noises

The purpose of the experiment was to study how the loudness (or annoyance) of the constituents in pairs of community noises combines into total loudness (or total annoyance). Three community noises (pile driving, jack hammering, street traffic) were combined pairwise at different sound levels. The observers judged the total loudness of the combined noises as well as the loudness of each component noise when heard alone. Three models of loudness (or annoyance) summation for noise were tested: a vector summation model, a model assuming that the loudnesses of the masked constituent noises add arithmetically, and a simple model stating that the total loudness equals the loudest of the component noises when heard alone. All three models fitted the data satisfactorily from a statistical point of view. The ’’loudest component’’ model was favored because it produced a prediction error of only 14% in the ’’worst case’’ and can, therefore, serve as a ’’rule of thumb’’ for many practical purposes.