Context: Amid the Coronavirus pandemic, the government has recently issued an advisory related to setting the ideal range for temperature of air conditioners and maintaining relative humidity.
More about the news:
- The guidelines were formulated by the Indian Society of Heating, Refrigerating and Air Conditioner Engineers (ISHRAE) taking into consideration the climatic regions of the Indian subcontinent.
- According to ISHRAE, the “best action” to limit the risk of infection by air was to ventilate indoor environments with outdoor air.
- Room Temperature:
- Set room temperature between 24 degrees Celsius and 30 degrees Celsius.
- For Humid close to 24 is desirable and for dry climates 30 or more is appropriate.
- Relative humidity:
- Maintain relative humidity between 40 percent and 70 per cent.
- The rooms should be kept ventilated even when ACs are not running.
- The guideline further said that the windows should be partly kept open while using electric fans.
Rationale behind the guidelines
- Range of temperature for survival of virus: Studies conducted have shown that -
- Low temperatures (7–8 degrees Celsius) were optimal for airborne influenza survival.
- Virus survival decreases progressively at moderate temperatures (20.5–24 degrees Celsius) and
- Virus survival further decreases at higher (greater than 30 degrees Celsius) temperatures.
- Survival of virus on surfaces: Guidelines also quotes a study which has shown that the SARS-CoV-2 can live for
- 14 days on a surface at 4 degrees Celsius,
- One day at 37 degrees Celsius and
- Will die in 30 minutes at 56 degrees Celsius.
- Association with the humidity
- Humidity can affect the infectivity (the ease with which infections can take place)of the virus through respiration.
- In a dry environment, or when there is low humidity, it is easier for foreign particles to invade the body.
- Therefore, relative humidity of at least 40 per cent is considered the threshold.
- Guidelines also refers to studies which indicate that relative humidity of 80 per cent and above can neutralise the virus.
Dry air and vulnerability to infections:
- When we breathe dry air the mucous membrane in the lungs becomes dry.
- The fluid over lining the cells becomes more viscous, and the little hairs called cilia, which protect our lungs from deep settling of viable and non-viable particles, cannot work and particles settle more deeply in the lungs.
- If we consider oxygen and CO2 transport and the blood, it is only one cell membrane that separates the airspace from the blood.
- So, if something goes from our lungs into the blood, we get infected.
- Water vapour present in the air is known as humidity. It is expressed quantitatively in different ways.
- Absolute Humidity:
- The actual amount of the water vapour present in the atmosphere is known as the absolute humidity.
- It is the weight of water vapour per unit volume of air and is expressed in terms of grams per cubic metre.
- Relative humidity:
- The percentage of moisture present in the atmosphere as compared to its full capacity at a given temperature is known as the relative humidity.