Control is to be such that under normal operating conditions concentrations of solvent vapor in the customer area of all automatic dry-cleaning establishments shall not exceed 0.4 of the applicable threshold limit value established by the American Conference of Governmental Industrial Hygienists and, in the maintenance area, shall not exceed the full threshold limit value. The use of devices or substances which tend to mask the solvent odor shall be prohibited.
('69 Code, § 5-30)