The Principle of Ultraviolet Sterilisation
Ultraviolet radiation acts on the genetic material—DNA—of living cells, causing damage to the DNA and resulting in the death of bacteria; furthermore, ultraviolet radiation within specific wavelength ranges reacts with oxygen in the air to produce ozone, which has strong oxidising properties, thereby killing bacteria.
What are the common types of ultraviolet light sources used for disinfection?
Traditional UV disinfection light sources are low-pressure mercury lamps with a central wavelength of 253.7 nm. Although UVC LEDs have not yet reached medical-grade standards, they are expected to become the next generation of products as advancements continue to be made in wavelength and light output technology.
Can ultraviolet light kill coronaviruses?
Coronaviruses are protein-enveloped, single-stranded, positive-sense RNA viruses; apart from the novel coronavirus (2019-nCoV) recently identified, the best-known examples include the SARS and MERS coronaviruses.
Research conducted during the SARS outbreak found that the SARS virus is sensitive to heat radiation and UVC; exposure to UVC at an intensity of more than 90 μW/cm² for 30 minutes is sufficient to inactivate the SARS virus.
Researchers also simulated natural sunlight in the laboratory and found that, under clear skies in Beijing at 10.00 am in May—when ultraviolet intensity was 4–5 µW/cm²—the coronavirus could be inactivated in vitro within three hours.
What type of ultraviolet light can be used for disinfection?
Research indicates that the UVC spectrum (200–280 nm) is the portion of ultraviolet light that possesses bactericidal properties. The bactericidal efficacy of wavelengths varies depending on the organism and its life stage. Ultraviolet light is highly effective in killing pathogens that cause major infectious diseases such as cholera, dysentery and enteritis. According to technical standards for disinfection and sterilisation, each type of microorganism has its own specific UVC inactivation dose standard (irradiation time × intensity).
How long does it take to disinfect using an ultraviolet lamp?
When using an ultraviolet lamp for disinfection, the duration of the disinfection process should be determined by the temperature and humidity of the room. Generally speaking, the disinfection time should not be less than 30 minutes. In particular, the disinfection time should be extended when the temperature is below 20 °C or above 40 °C, or when the relative humidity exceeds 60%.
What precautions should be taken when using UV lamps for disinfection?
1. Ultraviolet light must not come into direct contact with human skin
2. Ultraviolet disinfection lamps must be installed in accordance with the regulations
3. Keep the UV lamp tubes clean; wipe off dust and grease with a lint-free cloth
4. When low-pressure mercury-vapour lamps are used for UV sterilisation and disinfection indoors, they produce ozone, which is harmful to human health; windows must therefore be opened to ventilate the room.
5. UV lamps are consumables and will lose their effectiveness within a year; it is recommended that they be replaced with new ones when they reach the end of their service life.
What are the factors that affect the effectiveness of UV sterilisation and disinfection?
1. The wavelength range of ultraviolet light
2. The type of UV lamp and whether a reflector is fitted
3. The degree of soiling on the lamp tubes
4. Irradiation time, intensity and distance
5. Temperature and humidity
How to deal with the harm caused by ultraviolet radiation to the human body
1. Skin burns:
Symptoms: redness of the skin, pain, marked tenderness, exudate or oedema, etc.
Treatment: For minor burns, apply a cold compress immediately; symptoms will generally subside within 24 hours. In the case of severe burns, seek immediate medical attention for anti-inflammatory and anti-allergy treatment.
2. Photokeratitis
Symptoms: If you experience a foreign body sensation or a worsening burning sensation in the eye, accompanied by severe pain, photophobia, tearing, eyelid spasms, conjunctival redness or bulbar conjunctival oedema, you should seek medical attention.
Overall, in theory, ultraviolet light should be capable of inactivating the novel coronavirus (2019-nCoV). The recently published ‘Diagnosis and Treatment Guidelines for Pneumonia Caused by Novel Coronavirus Infection (Trial Version 4)’ also states that the virus is sensitive to ultraviolet light and heat [7].
However, with regard to the common form of the virus found on droplets, there are no clear studies indicating exactly how effective ultraviolet light is.
Therefore, in the face of the current pandemic, wearing a face mask, washing your hands frequently and ensuring good ventilation may still be the most reliable ways to prevent infection. If you need to install and use ultraviolet disinfection equipment, you must adhere to the relevant operating guidelines and take care to avoid causing harm to people.
