A review of indoor air quality in heritage buildings and confined spaces: Implications for occupational safety and health

The quality of indoor air environments in heritage buildings and confined spaces, such as tunnels, is a critical concern for occupational safety and health (OSH). These environments often contain airborne contaminants, including particulate matter (PM2.5 and PM10), heavy metals, silica, asbestos, bacteria, fungi, and microplastics, which pose serious health risks to workers and visitors. The deterioration of building materials, inadequate ventilation, and resuspension of settled dust contribute to poor indoor air quality (IAQ), leading to long-term exposure hazards. Heritage buildings, constructed with materials such as lead-based paint, asbestos insulation, and decaying wood, release hazardous particles into the indoor environment over time. Meanwhile, confined spaces like tunnels experience high concentrations of silica dust, toxic gases, and microbial proliferation, exacerbating occupational exposure risks. Recognizing the importance of IAQ to occupational health, regulatory bodies such as DOSH Malaysia have introduced the Industry Code of Practice on Indoor Air Quality (ICOP 2010, revised 2024) to establish workplace IAQ standards. The ICOP 2010 guidelines emphasize the importance of monitoring airborne pollutants, maintaining adequate ventilation, and implementing mitigation measures to minimize health risks indoors and enclosed workspaces (DOSH, 2024). This review analyzes the sources, distribution, and health effects of IAQ degradation in historical and enclosed environments and evaluates existing regulatory frameworks, including ICOP 2010, in addressing these concerns. It compares IAQ standards with regulatory exposure limits set by organizations such as ICOP 2010, the Occupational Safety and Health Administration (OSHA), and the World Health Organization (WHO). The health effects of prolonged exposure to PM-bound heavy metals, asbestos fibres, and microbial contaminants are discussed, with particular emphasis on respiratory diseases, lung cancer, and neurological impairments. The paper also evaluates IAQ management strategies, including real-time air quality monitoring, ventilation improvements, filtration technologies, and personal protective equipment (PPE). It highlights the effectiveness of mitigation methods in reducing occupational exposure and proposes future research directions to develop sustainable IAQ solutions in heritage conservation and underground infrastructure projects. Aligning IAQ control measures with ICOP 2010 guidelines ensures that workplaces adhere to best practices for safeguarding worker health, preserving historical structures, and maintaining regulatory compliance.