The ventilation requirements of Article 2.4.2.5. are intended to address the specific hazards due to manure gases in farm buildings housing livestock with below-floor storage of liquid manure. Where these requirements are met, it is not necessary to apply the provisions of Articles 6.3.1.5. and 6.9.1.2. with respect to manure gases. However, where the farm building contains other hazardous substances (air contaminants or hazardous gases, dusts or liquids), the provisions of Articles 6.3.1.5. and 6.9.1.2. must be applied with respect to those substances.