Notwithstanding the provisions of N.H. Rev. Stat. § 154:7, 8, and 9, no person therein authorized to compel assistance by conscription shall order any person under the age of 18 years or over the age of 45 years (except where such person has voluntarily consented to accept direction and if under the age of 18, has furnished parental consent in writing); or any person having a physical or mental disability or who is otherwise disabled in capability to perform any act of firefighting which would subject such person to the possible risk of grievous bodily injury, harm or death, except in a dire emergency, and then only if such act or acts are deemed necessary to protect and preserve public property endangered by fire, or in the case of a national emergency. Notwithstanding this limitation, nothing in this section shall be construed to limit a person’s ability, if over 18 years of age, to voluntarily consent to perform acts of firefighting so long as such person agrees to accept direction of qualified firefighters and the person accepting the consent is authorized by N.H. Rev. Stat. § 154:7, 8, and 9, to call for such assistance and reasonably believes that the person volunteering understands the personal risk.