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.

Guidelines Issued

  • 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.


About Humidity

  • 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. 

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