(c) Before and until the effective date of the rule described in paragraph (b) of this subdivision, for the purposes of the department of health and mental hygiene finding unsafe lead paint in a dwelling unit or a covered facility, as defined in section 17-920, and issuing an order to abate a condition in a dwelling unit where a child of applicable age with an elevated blood lead level resides or to abate or remediate a condition in a covered facility where a child of applicable age with an elevated blood lead level is routinely present for 10 or more hours per week, pursuant to section 173.13 of the health code, nothing in this article shall prevent the board of health from determining that unsafe lead paint may include paint with a concentration of lead content that is less than the concentration of lead content in paint set forth in paragraph (a) of this subdivision. Such a determination of unsafe lead paint may include paint with a concentration of lead content no less than 0.5 milligrams of lead per square centimeter, as determined by laboratory analysis, or by an x-ray fluorescence analyzer. X-ray fluorescence readings shall be classified as positive or negative in accordance with the manufacturer's instructions. If laboratory analysis is used to determine lead content, results shall be reported in milligrams of lead per square centimeter. Where the surface area of a paint chip sample cannot be accurately measured or if an accurately measured paint chip sample cannot be removed, a laboratory analysis may be reported in percent by weight. For such purposes, such concentration determined by the board of health pursuant to this paragraph shall be no less than 0.25 percent of metallic lead, based on the non-volatile content of the paint or other similar