Quantification and characterisation of Belgian offshore wind farm operational sound emission at low wind speeds

Offshore renewable energy installations contribute to the continuous underwater sound that has been identified as an environmental concern under the EU Marine Strategy Framework Directive. This study quantified, characterised and compared the continuous underwater sound emitted by steel jacket foundation and monopile Wind turbines during operation at low wind speed (0-12 m/s). The operational sound emitted by a monopile founded and a jacket founded wind farm in the BPNS showed a maximum increase of SPL of about 20 dB re 1 µPa. Spectral analysis showed that this increase occurs at frequencies below 3 kHz. Steel monopile foundations even when equipped with a less powerful generator, emitted significantly more underwater sound than jacket foundations. The addition of underwater sound is increasing with wind speed with a rate dependent of the type of foundation, with monopiles showing a stronger increase with wind speed than jacket foundations. Possible impacts on marine life like fish, marine mammals or invertebrates remain unclear mainly due to the lack of knowledge in disturbance or behavioural response levels for the species that could be found on these sites. Future challenges are to expand the study to higher wind speeds (study ongoing) and to quantify and qualify the additional sound pressure of a larger wind farm or a series of adjacent smaller wind farms (i.e. cumulative effects)

The closed circuit rebreather (CCR): is it the safest device for deep scientific diving?

The closed circuit rebreather (CCR) is not a new diving technology. From the late 1990s CCR units were commercially available in Europe, and increasingly more divers, and among them scientific divers, have been trained to use them. Even if many benefits exist for using CCR for all diving depth ranges, it is in the deep diving zone ranging from 50 m to 100 m of sea water where the main advantages to using this equipment exist. Using rebreathers does carry additional risks, and these must be mitigated to ensure safe usage. A standard for CCR scientific diving has existed for many years in the USA, and the levels of expertise within the European scientific diving community are now sufficient for a European standard to be established. National legislation for occupational scientific diving in many cases excludes CCR diving, which can limit its use for scientific purposes. This paper suggests that, where possible, legislations should be allowed to evolve in order to include this type of equipment where and when its use has direct advantages for both the safety and the efficiency of scientific diving. This paper provides a brief description of the fundamentals of closed circuit rebreather diving and outlines the benefits that its use offers diving scientists. Special attention is given to safety issues with the assertion that the CCR concept is, if strictly applied, the safest available technique today for autonomous deep scientific diving purposes