Original Research
Environmental Ergonomics

Level of Indoor Air Quality Among Malaysian Commuter Users: A Case Study

Background and Context

Public transportation is an essential component of Malaysia’s strategy to reduce traffic congestion, lower carbon emissions, and improve urban mobility. The KTM Komuter (Keretapi Tanah Melayu Komuter) service is one of the oldest and most heavily utilised rail-based transit systems in the Klang Valley metropolitan area, serving hundreds of thousands of commuters daily on routes connecting suburbs and satellite cities to Kuala Lumpur’s central business district. The introduction of women-only coach carriages in 2010 was a significant policy initiative aimed at improving safety and comfort for female passengers.

Despite the growing ridership, research on the environmental quality inside Malaysian commuter train cabins has been remarkably sparse. Passengers who spend significant time in enclosed train compartments — often during crowded peak hours — are exposed to whatever air quality conditions exist within those spaces. In poorly ventilated or overcrowded carriages, indoor air pollutants can accumulate to levels that exceed health-based guidelines, potentially causing or exacerbating respiratory symptoms, headaches, fatigue, and reduced cognitive function.

Carbon dioxide (CO₂) is a particularly important indicator of indoor air quality in occupied spaces. While CO₂ itself is not toxic at the concentrations typically encountered in buildings and vehicles, elevated CO₂ levels serve as a reliable proxy for inadequate ventilation — and by extension, for the potential accumulation of other pollutants including bioaerosols, volatile organic compounds, and particulate matter generated by human occupancy. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 62-2001 recommends that indoor CO₂ concentrations should not exceed 1,000 ppm above outdoor levels, a threshold that is widely used as a benchmark for acceptable ventilation in occupied spaces.

Study Design and Methods

This field study was conducted aboard the KTM Komuter service during peak-hour operations on weekends. The research team rode the train for a complete two-hour journey covering 18 main stations along the route (which extended from Kuala Lumpur Sentral to destinations including Tampin and Port Klang). Measurements were taken in the women’s coach cabin, with instrumentation placed at the centre of the carriage to obtain representative readings.

The primary measurement instrument was an Air Quality Meter (Airflow Instrument Model TA465), a calibrated direct-reading device capable of simultaneously monitoring multiple parameters. The three main IAQ parameters measured were temperature (°C), relative humidity (%), and carbon dioxide concentration (ppm). Additionally, the research team manually counted the number of passengers boarding and alighting at each station to establish occupancy levels throughout the journey.

Data were collected during both morning and evening peak hour periods to enable temporal comparisons. Statistical analysis examined the relationships between passenger numbers and IAQ parameters using regression analysis, with R² values calculated to quantify the strength of the passenger–pollutant relationship.

Principal Results

The most significant finding was that CO₂ concentrations during morning peak hours exceeded the ASHRAE standard limit of 1,000 ppm at several points along the route, particularly at stations where large numbers of passengers boarded (such as Kuala Lumpur Sentral). The 43.8% differential between morning and evening CO₂ readings reflects the higher passenger loads typical of morning commutes, when workers and students simultaneously travel toward central employment and educational districts.

The positive correlation between passenger numbers and CO₂ concentration was demonstrated through regression analysis. The regression line and R² value confirmed that the number of passengers was a significant predictor of cabin CO₂ levels. This finding has straightforward mechanistic logic: each exhaling passenger contributes approximately 200 mL of CO₂ per minute to the cabin atmosphere, and when the ventilation system’s air exchange rate is insufficient to dilute this accumulation, concentrations rise proportionally with occupancy.

Relative humidity was also notably higher during morning hours (17% greater than evening readings). Elevated humidity in enclosed train cabins results from passenger respiration and perspiration, compounded by Malaysia’s already humid tropical climate. High humidity reduces thermal comfort, promotes the proliferation of dust mites and mould spores, and can exacerbate respiratory symptoms in susceptible individuals. The combination of elevated CO₂ and high humidity during morning peak hours represents a dual environmental stressor for commuters.

Temperature showed the opposite temporal pattern, with evening readings approximately 3% higher than morning values. This likely reflects the ambient temperature increase over the course of the day and the heat load from the air conditioning system operating at capacity during afternoon hours.

Public Health Implications

For the millions of Malaysians who rely on rail transit for their daily commute, the air quality inside train carriages is not a trivial concern. Commuters who spend 45–90 minutes each way in these enclosed environments are exposed to indoor air conditions that may not meet international health standards, particularly during crowded morning services. Short-term health effects of elevated CO₂ and poor ventilation include headache, drowsiness, reduced concentration, and respiratory irritation — symptoms that can impair productivity and wellbeing throughout the workday.

The findings provide an evidence base for recommending improvements to the KTM Komuter’s ventilation systems. Specific interventions could include upgrading HVAC (heating, ventilation, and air conditioning) systems to increase fresh air intake rates, implementing CO₂-based demand-controlled ventilation that adjusts airflow in response to real-time occupancy levels, improving door sealing to prevent humidity ingress at stations, and increasing service frequency during peak hours to distribute passenger loads across more carriages. A subsequent study on Malaysia’s MRT system found that CO₂ concentrations during peak hours reached up to 1,380 ppm, indicating that the issue extends beyond the KTM Komuter to other rail transit systems.

Limitations

This study was conducted during weekend peak hours, which may not fully represent weekday conditions when ridership is typically higher. Measurements were taken on a single route and in the women’s coach only — conditions in mixed-gender coaches or on other routes may differ. The study measured only three IAQ parameters; a more comprehensive assessment would include particulate matter, volatile organic compounds, biological contaminants, and carbon monoxide. The research did not include a health outcomes component — associations between measured IAQ levels and passenger symptoms were not assessed. Environmental conditions vary with season, weather, and train age/maintenance status, and this single-day study cannot capture the full range of conditions experienced by regular commuters.

← Back to MJPHM Homepage