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Time to take a rain check?
05 March 2019
All forms of elevated noise in an industrial setting present a serious occupational hazard. Anthony Barnett, technical marketing manager at Armacell, looks at why the source of the problem is not always as obvious as you may think.
A much overlooked cause of disturbance in the industrial setting is that from airborne and structural noise from rainwater systems. Sound waves from these elements can reach elevated levels, resulting in safety issues because it blocks out devices that are there to protect the safety of workers, for example, machine alarms, forktruck reversing signals and human voices.
The majority of industrial buildings were constructed before any consideration was given to noise from rainwater, meaning that there are now tens’ of thousands of facilities where noise from rain regularly exceeds 70dB - similar to typical street traffic.
Intense and heavy rain
The draft standard created by the BRE, BS EN ISO 140-18:2006, outlines the level of noise generated from a roof under certain conditions. It uses two types of rainfall: Intense and Heavy. A rainfall rate of 40mm per hour (mm/h) is classed as ‘intense’ and occurs once every 50 years. ‘Heavy’ rain has a rainfall rate of 15mm/hour and occurs once every two years. Although, during a storm, rainfall rate is rarely constant. Often the most intense rain will fall for only a few minutes before easing off to heavy or gentle rain. The noise generated from rainwater either on metal profiled sheeting or as it traverses guttering, downpipes and drainage is related to; rainfall rate (11mm/h), drop diameter (mm) and fall velocity (metres per second).
Thanks in part to work done by BRE and other building research bodies, as well as a greater awareness of the problem that rainwater can cause, more attention is now being given to its impact. A consequence of this is that there are now companies that offer a range of solutions and the most effective is when both the profiled sheeting and rainwater system are fitted with sound attention materials. Doing one without the other will mean that the problem still exists - it is still common for the rainwater system to be overlooked however, once it leaves the roof, water causes serious airborne and structural noise as it passes along guttering and cascades through downpipes.
One of the challenges is that the majority of industrial buildings in the UK are older stock and because of that few have any noise mitigation on roofing elements. The insulation industry has responded by developing flexible technical insulation materials that are designed specifically for attenuating noise in these situations. Material such as the ArmaComfort AB Alu Plus product consists of a 2mm thick foil faced acoustic EPDM-EVA barrier with 4kg/m2 weight and a 9mm elastomeric foam layer for decoupling. In comparison to traditional acoustic insulation products, tests show that these types of flexible insulation foams, fitted around rainwater systems and drainage pipes, achieve a much greater reduction in sound level, and with a thinner wall thickness.
Independent tests by CSTB (Centre Scientifique et Technique du Bâtiment) confirmed that these acoustic foams are able to reduce the airborne sound pressure levels of a Geberit roof drainage system by 16 dB (A) at 2 l/s water flow. Similar tests on a PVC pipe, where the vibrations caused by flowing water are stronger because of the lighter weight PVC, achieved a noise reduction of 12 dB (A). The human ear perceives a reduction of 10 dB (A) as halving the volume. By choosing the correct flexible acoustic foam it is possible to achieve a weighted sound reduction index (Rw) up to 28 dB when pipe and pipe elbows are insulated.
Here comes the rain
Acoustic foam materials have good acoustic damping and acoustic isolation properties across the frequency range relevant for building acoustics – irrespective of whether it is installed on cast iron or PVC rainwater and waste water pipes. They also display very good fire behaviour, achieving the best fire class for organic products in the European SBI test.
As sound mitigation on industrial processes becomes ever more effective, noise from rain will grow relative to this. For the tens of thousands of existing industrial buildings as well as new builds, any materials that tackle this issue will be making an important contribution to occupational health and welfare. It is therefore essential that noise abatement measures in the form of thin acoustic lagging are consistently planned and properly carried out, both when constructing new buildings and when modernising existing ones.
As awareness of noise from roofing and rainwater elements increases, and the uptake of acoustic foams becomes widespread, that most British of things - rain - will become less of a problem.