Every successful project starts with a framework. A vision statement. A blueprint. The editors of Engineered Systems are proud to present The Blueprint — a monthly Q&A interview with HVACR engineering’s leading voices. These one-on-one discussions will examine the trade’s history, current industry trends, the factors shaping the sector’s future, and more.
Managing noise remains an enduring concern for worker safety, particularly in the industrial setting. According to an estimate by the U.S. Center for Disease Control (CDC), 22 million workers are exposed to potentially damaging noise annually. Some ways to safeguard employees from noise in industrial spaces include isolating noise sources, limiting employee exposure, and making sure employees wear protective equipment.
Researchers are looking at how interventions to reduce noise in the industrial workplace, including the design of pipe insulation and jacketing combinations on industrial pipes, can contribute to solutions that reduce noise.
Kevin Herreman, principal acoustic scientist at Owens Corning, sat down with Herb Woerpel, editor-in-chief, Engineered Systems, to discuss the problems posed by industrial noise and shares some research on models to more accurately predict insertion loss in the latest installment of the Blueprint.
Engineered Systems. Welcome, Kevin. Let’s jump right in. Beyond hearing loss, what are some issues the World Health Organization (WHO) has identified relevant to noise?
Kevin Herreman: Beyond the potential for hearing loss and requirements for hearing protection in work areas, sustained exposure to high noise levels has been related to multiple health issues. According to the World Health Organization Guidelines for Community Noise2, these health effects can lead to social handicap, reduced productivity, decreased performance in learning, absenteeism in the workplace and school, increased drug use, and accidents.
From a cognition perspective, mental activities involving working memory, such as sustained attention to multiple cues or complex analysis, are all directly sensitive to noise, and performance can suffer as a result. Noise also presents consistent after-effects on cognitive performance with tasks such as proofreading or persistence in solving challenging puzzles. Epidemiological studies show that cardiovascular effects occur after long-term exposure to aircraft or road traffic noise with LAeq,24h values of 65-70 dB. It’s interesting to consider that the risk for nose-induced hearing impairment increases when noise exposure is combined with certain factors common in industrial applications, including vibrations and chemicals. In these circumstances, long-term exposure to LAeq, 24h of 70 dB may induce hearing impairment.
Engineered Systems: How do businesses typically try to reduce noise levels in their plants?
Herreman: Absorptive approaches to reducing noise can include adding absorptive panels to ceilings or walls. Some more enlightened approaches include purchasing low noise equipment. The National Institute for Occupational Safety and Health and the NASA Buy Quiet website offer resources to support purchasing decisions. Many times, companies will build an enclosure around a noise emitting area to trap the sound. If the enclosure does not prove effective, adsorption may be added around the equipment. However, this approach can potentially interfere with equipment cooling.
Engineered Systems: What approaches can help reduce machine noise in industrial spaces?
Herreman: One thing to keep in mind is that the closer the intervention is to the noise source, the more effective the treatment will be at reducing noise. Depending on the equipment, a sound-attenuating blanket may be effective in reducing noise transmission. A more involved alternative is to add an enclosure with sound insulation on the interior facing the sound emitting equipment.
Prescriptive solutions for jacketing on pipes, including the combination of materials, can help mitigate noise transmission and the amount of noise radiated into a space. Owens Corning recently presented findings from extensive research at InterNoise2021. Researchers executed 32 ISO 15665 tests at the GRYFITLAB Acoustic Laboratory in Poland to evaluate the effect of different jacketing and insulating material combinations to identify the impact of the changes on the insertion loss result.
The results of the testing shed light on approaches that can help predict insertion loss relative to the ISO 15665 standard. While ISO 15665 specifies a testing process for measuring the acoustic performance of installed and jacketed pipe insulation systems, the expense involved in testing to this standard can be quite high.
Engineered Systems: What ASTM and ISO standards are in place for the design and installation of acoustic insulation used on pipes?
Herreman: ASTM E1222, “Laboratory Measurement of the Insertion Loss of Pipe Lagging Systems,” uses a closed end pipe with a minimum diameter of 305 mm (12 in.) to identify the insertion loss of the pipe insulation versus frequency.
Additionally, ISO 15665, “Acoustic Insulation for Pipes, Valves, and Flanges” describes testing for insertion loss using a pipe that transitions through a test chamber with no end reflections. The standard classifies the insertion loss across several frequency bands for pipe insulation via a rubric. In addition, it also prescribes general treatment designs for each performance class for each of the three sizes of pipe diameter up to 1,000 mm (39.5 in.).
Engineered Systems: How does insertion loss serve as a model to evaluate an acoustic piping design?
Herreman: In testing applications, insertion loss represents the difference between the sound level measured in the testing chamber between an untreated pipe in comparison to its sound level measurement after the pipe is treated with an insulation and jacketing approach. Taking the octave band values for the insertion loss and comparing them to the table provided in ISO 15665, for the diameter of pipe tested, will inform what class of pipe insulation (A, B, C, or D) to apply. The classes identify a minimum (A) to a maximum (D) performance of the pipe insulation.
Engineered Systems: How is research leading to a new model for estimating the acoustic performance of pipe insulation in industrial spaces?
Herreman: There are only a few acoustic research facilities in the world equipped to do the extensive studies needed to comprehensively evaluate insertion loss. With this in mind, Owens Corning spent nearly a year testing 32 different combinations of mineral wool and cellular pipe insulation, loaded vinyl, and jacketing developments in high- and low-temperature systems. The research was conducted at acoustic facilities in the Netherlands and Poland. As much of the data in the market today is based on prescriptive designs identified in the ISO 15665 standard, the new findings provide an impactful expansion to the number of pipe-insulating designs available in the market.
Engineered Systems: How will these studies contribute to options for managing noise in the future?
Herreman: More options, improved economics, and more accurate predictions are three benefits of the testing. As much of the data in the market today is based on prescriptive designs identified in the ISO 15665 standard, these studies significantly expand the number of design options available in the market. The testing also reinforced the high investment required to develop new designs and afforded the opportunity to create a simple statistical model to predict performance, accounting for almost 95% of the variation between tests. Modeling is an attractive proposition when developing designs as multiple models can be evaluated at little or no cost and the prediction of insertion loss was very good.
Engineered Systems: How did the development of a new model significantly improve the accuracy of ISO 15665 classification?
Herreman: The initial statistical model was only successful at predicting the performance class per the ISO 15665 standard 66% of the time. Thus, to improve the predictive results, a theoretical model was developed and validated using the extensive data from the testing. This combination of a theoretical and statistical model provided a very high level of predictability for the performance class of a combination of materials and jacketing on a pipe.
Engineered Systems: How may findings on insertion loss be used to optimize future pipe insulation designs and eliminate the need for testing and associated costs?
Herreman: Traditionally, the market has had few design options for the largest diameter of piping described in the ISO 15665 standard. We’ve already expanded the use of the model by validating it for the largest diameter pipes. As the number of designs available in the market expands, owners, operators, and installers will have more options for lowering noise levels in the industrial environment. The model has also provided insight into the interactions between each layer of various designs. New insights will allow us to continue to explore designs that optimize performance.