{'fraction_non_alphanumeric': 0.018201284796573874, 'fraction_numerical': 0.02462526766595289, 'mean_word_length': 4.933333333333334, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Measuring the noise attenuation of shotblasting helmets.

Air-fed blasting helmets are used in abrasive blasting operations to provide essential face, eye and respiratory protection. BS EN 271: 1995 (equivalent to the European Standard EN 271: 1997), the standard that deals with the construction of blasting helmets, addresses the above matters and also the problem of noise generated by the breathing air supply. However it has no requirements for manufacturers to measure or report the helmet's ability to attenuate the very high levels of noise generated by the blasting process. The aim of the project was to develop a test method to measure the noise attenuation of shotblasting helmets. The method developed is an objective measurement, using a head and torso simulator (HATS), which provides a suitable means for helmet manufacturers to report their product's ability to attenuate blasting noise. The results from this project showed that the HATS currently prescribed by BS EN 271: 1995 can be used for measuring the noise attenuation of helmets against typical shotblasting noise. Using such a HATS in the proposed test method will give attenuation values that correlate well with those measured using human subjects. Therefore the HATS already used by manufacturers to show compliance of their product with BS EN 271: 1995 could also be used to provide information on the helmet's noise attenuation. Results from this project also showed that the same HATS can be used, in place of human subjects, to measure the air supply noise according to the method defined in BS EN 271: 1995. BS EN 271: 1995 is due for revision in 2000. The results from this work should be used to influence future revisions of the standard so that requirements to measure and report noise attenuation of shotblasting helmets are considered, a major omission in the present standard.