Hygiene Evaluation of Air and Ventilation

Chemical Composition and Significance

Adults inhale 13-14 m3 of air daily, making air composition vital. Atmospheric air is a gas mixture; composition changes with foreign chemicals. Table 1 (provided in the transcript) details the composition of atmospheric air. Air composition changes in residences due to occupants and household processes. Production and agriculture can introduce harmful vapors and gases. Air density decreases with altitude, reducing gas content per unit volume.

Normal Components of Air

Nitrogen, oxygen, carbon dioxide, and inert gases are key. Nitrogen dilutes oxygen; pure oxygen is harmful. It doesn't support respiration/combustion and remains constant in the atmosphere. High nitrogen concentrations can be fatal. The nitrogen cycle involves atmospheric nitrogen converting to nitrogen oxides via electrical discharges, then to organic compounds in soil, and back to the atmosphere during decomposition. Nitrogen is a nutrient for plants, utilized by legumes and absorbed by blue-green algae and soil bacteria.

Oxygen

Oxygen is crucial for breathing, delivered via oxyhemoglobin. A person absorbs 12 liters per hour at rest. Exhaled air has 25% less oxygen. Oxygen is replenished by atmospheric reserves and photosynthesis. Water molecule disintegration under sunlight also produces oxygen. Oxygen content in buildings remains stable due to diffusion, even with poor ventilation, with insignificant physiological impact. However, sealed spaces can experience reduced oxygen, causing hypoxia. Concentrations of 15-17% cause deterioration, and 7-8% can be fatal.

Ozone

Ozone (O3) is a strong oxidant formed by UV radiation, lightning, and water evaporation. It protects against harmful UV radiation in the stratosphere. While a sign of air purity, excess ozone is an irritant. In polluted cities, ozone indicates smog formation via photochemical reactions. Ozone layer depletion is caused by CFC emissions, which release chlorine atoms that break down ozone molecules, increasing UV radiation on Earth.

Carbon Dioxide

$CO2$ is released during respiration, combustion, fermentation, and putrefaction. Its atmospheric constancy (0.03-0.04%) is maintained by plant absorption, dissolving in water, and atmospheric precipitation. Oceans play a role by dynamically balancing $CO2$ levels. $CO2$ is a physiological activator of the respiratory center. Exhaled air has 100 times more $CO2$ than inhaled air. An adult exhales 22.6 liters per hour at rest, increasing with physical activity.

Concentrations of 0.7-0.8% in poorly ventilated areas are not harmful, but 4-5% causes symptoms like headache and increased blood pressure. High $CO2$ concentrations can cause narcotic effects; 8-10% can be fatal. Such levels occur in sealed spaces or industries with high $CO2$ release.

Maximum Permissible Concentration of Carbon Dioxide

The maximum permissible concentration (MPC) of $CO_2$ is 0.1% for residential/public buildings and 0.07% for medical facilities.

Carbon Dioxide as a Sanitary Indicator

While $CO2$ and oxygen levels may not drastically change in poorly ventilated rooms, other factors like temperature, humidity, dust, germs, ionic composition, and anthropotoxins do. These cause stuffiness and health issues. Since $CO2$ is easily measured and changes in parallel with these factors, it indicates air purity.

Greenhouse Effect

The greenhouse effect, described by Fourier in 1824, is the temperature increase on a planet due to greenhouse gas accumulation. Moderate greenhouse gas concentration is vital for life. These gases trap thermal radiation. Increased greenhouse gases from civilization could cause excessive heating.

Without the greenhouse effect, Earth's average temperature would be 255 K (-18°C or 0°F). The actual average is approximately 15°C. Infrared rays heat the Earth. Greenhouse gases trap infrared rays, increasing Earth's temperature.

Greenhouse Gases

Key greenhouse gases include:

Carbon dioxide ( $CO_2$ ): accounts for 80% of greenhouse gases, from natural (volcanoes, decay) and anthropogenic sources, increasing 149% since the industrial revolution.
Methane ( $CH4$ ): 25 times more potent than $CO2$ , from hydrocarbon extraction, livestock, and rice plantations; concentrations up 262% from pre-industrial levels.
Nitrous oxide ( $N2O$ ): from farming, fossil fuels, and waste; absorbs infrared radiation 310 times more strongly than $CO2$ .
Tropospheric ozone ( $O_3$ ): an air pollutant that enhances the greenhouse effect.
Water vapor: concentration depends on temperature; absorbs and reflects heat.
Synthetic substances: from the chemical industry, including halogenated hydrocarbons and hydrofluorocarbons.

Reasons for Increasing the Greenhouse Effect

Reasons include the use of fossil fuels, increased livestock, deforestation, waste accumulation, nitrogen fertilizer application, vehicle exhaust, and population growth.

Consequences of Global Warming

Consequences are rising sea levels, increased natural disasters, extinction of species, low yield, and ocean acidification.

Ways to Solve the Greenhouse Effect

Solutions include reducing emissions, using energy-efficient technologies, employing environmentally friendly farming, switching to zero-emission vehicles, and stopping deforestation.

Ventilation

Ventilation is crucial for health, removing pollutants like carbon dioxide, sweat degradation products, and chemicals from building materials. Poor ventilation can cause headaches and reduced working capacity. Ventilation systems remove contaminated air and supply fresh air, maintaining optimal air parameters. Proper ventilation should limit carbon dioxide to 0.1% for living and public spaces and 0.07% for hospitals.

Ventilation Systems

Ventilation is airing, removing polluted air and replacing it with clean air. It's classified by scale (local, total, centralized, combined), stimulus (natural, artificial, mix), and method of supplying/removing air (supply, exhaust, supply-and-exhaust).

Natural ventilation relies on wind and temperature differences. Artificial ventilation uses fans. Mix ventilation combines both. Infiltration involves air penetration through gaps, while airing uses open windows and vents. The minimum vent area to floor area ratio for natural ventilation is 1:50. Short, frequent ventilation is better than constant opening in cold weather.

Artificial ventilation, using fans, is needed in crowded public buildings. Fan effectiveness depends on location; fans in vents improve ventilation. Supply ventilation brings air in, exhaust removes air, and supply-and-exhaust does both.

Supply-and-exhaust systems can prioritize supply or exhaust. Predominant supply maintains positive pressure and prevents contaminated air intrusion. Predominant exhaust prevents harmful emissions from spreading. Positive pressure rooms have higher supply than exhaust. Negative pressure rooms have higher exhaust.

Negative pressure rooms isolate airborne viruses by maintaining lower pressure than surrounding areas. Exhaust air passes through filtration. Precise pressure control is achieved via air valves, sensors, and monitoring systems.

HRV/ERV systems remove stale air and bring in fresh air while retaining energy. HRV retains heat and dehumidifies in summer, suited for colder climates. ERV retains humidity, beneficial in both winter and summer.

Ventilation systems can be local(removes from source to prevent spreading in the room), general(creates the optimum weather condition throughout the room), centralized(covers the whole building), combined(sum of different ventillation systems).

Evaluating Effectiveness

Ventilation effectiveness is assessed by carbon dioxide content compared to MPC and ventilation multiplicity. Ventilation multiplicity is the number of air updates per hour. Actual multiplicity must meet or exceed necessary multiplicity. Equations are provided for calculating both.

Ventilation is effective only if carbon dioxide levels are within MPC and actual multiplicity meets requirements. If either measure fails, the ventilation is deemed ineffective.