Abstract
The respired air of a volunteer was analysed while he was wearing a variety of integral crash helmets. Observations were made with and without a protective balaclava, bib or scarf, or both.Rebreathing occurred and the peak inspired oxygen tension fell as low as 16-0 kPa (120 mm Hg) with a minimum inspired carbon dioxide of 2-1 kPa (16-0 mm Hg). Accessories worn or attached to the helmet which restrict airflow into the helmet should not be used. Attention should be paid to the "air conditioning" of helmets when worn with flameproof balaclavas and bibs.