(1) Spiral stairs shall have,
(a) handrails on both sides, the outer handrail being not less than 1 070 mm high,
(b) a clear width not less than 660 mm between handrails,
(c) risers that are not more than 240 mm high,
(d) treads that,
(i) are a minimum of 190 mm deep at a point 300 mm from the centre line of the inside handrail,
(ii) have a consistent angle and uniform dimension, and
(iii) turn in the same direction, and
(e) a clear height not less than 1 980 mm.
(2) Spiral stairs conforming to Sentence (1) are permitted to be used as the only means of egress where they serve not more than 3 persons.
(3) Except as permitted by Sentence (2), spiral stairs shall not serve as an exit.