No compensation shall be payable for any pulmonary disease arising out of the inhalation of organic or inorganic dust or fumes unless the claimant suffers disability as described in § 42-9-10 or § 42-9-20 and shall not be compensable under § 42-9-30; provided, however, in claims based on byssinosis the claimant must have been exposed to dust in his employment for a period of at least seven years.