In our first post on the QUV/uvc, we discussed why the QUV/uvc was designed and the differences between it and the QUV accelerated weathering chamber used for generations to conduct UV weathering studies. In this post, we’ll go over published UVC exposure cycles. In future posts, we’ll discuss considerations for designing your own UVC exposure cycle and ideas for future standardization in this area.
The main international standard for UVC exposures is IEC 60335-1, a broad safety standard for a variety of electrical appliances. Annex T includes a UVC exposure for materials including electrical insulation for wires or other components. The exposure requires “a conditioning apparatus and test procedure as specified in ISO 4892-1 and 4892-2,” with modifications. The most significant modification is that the xenon arc lamp, the heart of the ISO 4892-2 device, is substituted by a low-pressure mercury lamp. Unfortunately, this substitution changes not only the light source but the temperature characteristics of the control system. Leaving aside how one might improve this method for a future post, this standard includes exposure for 1000 hours at an irradiance of 10 W/m2 (1 mW/cm2) at 254 nm for a total dose of 3.6 kJ/cm2. The temperature is measured by a black panel thermometer and set to 63 °C, a value taken from the ISO standard.
Another published standard for a UVC exposure comes from the Business and Institutional Furniture Manufacturers Association (BIFMA), an ANSI accredited organization that writes standards for commercial furniture. BIFMA HCF 8.1-2019, Health Care Furniture Design Guidelines for Cleanability, includes a UVC exposure test to simulate regular UVGI (ultraviolet germicidal irradiation) disinfection protocols over the product’s service life. The test method requires an exposure dose of 291 kJ/m2 at 254 nm. Although it states the test duration is between 12 and 24 hours and therefore implies a specific irradiance range, BIFMA allows an exposure that achieves the dose faster, as long as this adjustment is noted in the test report.
The BIFMA standard does not specify an exposure temperature. However, the typical UVGI cycle simulated is performed on-site in a healthcare facility. Therefore, we recommend a test temperature of 30 °C to approximate the upper range of indoor temperatures, such as when the climate control system is temporarily turned off during disinfection and other regular maintenance. Keeping the temperature no higher than this level may be a good idea because some materials intended for indoor use are not suitable for higher-temperature protocols such as the IEC standard test cited above.
The BIFMA standard includes helpful information on the rationale for its exposure cycle. A specific bacterium known to cause infections in a healthcare setting has been shown to be killed to a 4-log (99.99%) reduction by exposure to 800 J/m2 (80 mJ/cm2) at 254 nm. The test cycle in the BIFMA standard assumes that a piece of furniture will be exposed to weekly UVC cleaning cycles at this over a 7 year expected service life, and this equals 291 kJ/m2, or 29.1 J/cm2, at 254 nm. Having been written prior to the COVID-19 pandemic, this method and its development appears particularly prescient, and the rationale for the exposure is sensible. However, given what has developed during the pandemic, higher UVC doses than assumed in this standard may be encountered in settings where UVGI is instituted. This will be covered in the next post in this series.
The IEC method cited above delivers 124 times the UVC dose of the BIFMA method (3600 J/cm2, compared to 80 mJ/cm2). The IEC method appears to be based on exposure of materials in an environment where UVC lamps operate frequently or continuously, such as within a germicidal UVC device, HVAC system with germicidal lamps, or UVC curing system. Given that this method covers electrical safety, the higher dosage seems reasonable when compared to the BIFMA standard, which is mainly concerned with appearance properties of furniture after cleaning.
Because neither of these methods were written specifically with the QUV/uvc in mind, translating some of the requirements into a test cycle program requires some explanation, which our applications team can assist with individually. Since most current interest in UVC exposures is for applications outside these two standards, the next post will discuss general test design considerations for QUV/uvc exposure protocols.
A Series: What is the QUV/uvc and why was it developed?
Read Part I.
You are reading Part II.
Read Part III.
Part IV will be discussed in future posts.