Mr Dyment said: “BS EN ISO 16890:2016 will transparently inform filter users of the filter efficiency compared to its predecessors (EN 779 in Europe and ASHRAE standard 52.2 in the US). In June 2018, EN779:2012 will be withdrawn, leaving ISO 16890:2016 as the current standard. The ASHRAE standard is also due to be replaced by the ISO standard in the near future.”

The ISO standard defines testing procedures and gives a classification system for air filters used in general ventilation equipment. The classification system is related to filter performance against three different particle size ranges (PM1, PM2.5 and PM10).

Mr Dyment explained: “For the first time, in ISO 16890:2016 we have an air filtration standard that actually tells people specifically what a filter does.

“For example a typical air filter of a class that is going to make a difference to indoor air quality is defined in the new standard as ‘ePM1 60 percent minimum’ where ‘e’ stands for the removal efficiency of the filter, PM1 is the range of particles (=/< 1µm in size), and 60 percent is the percentage of particles the filter will remove.

“Under the old European standard - EN 779:2012 - the equivalent filter would have been designated ‘F7’ which doesn't tell consulting engineers, designers and specifiers what the filter is capable of.”

Furthermore, test procedures for ISO 16890:2016 are more closely aligned to ‘real-world' filter performance, said Mr Dyment. The performance tolerance of the new standard is also set much tighter at five percent.

He added: “Because it is due to replace two competing standards from Europe and the US, ISO 16890:2016 also represents the first opportunity for global harmonisation in testing procedures and a classification system for air filters used in ventilation equipment.”

Particulate matter (PM) affects more people than any other airborne pollutant. PM consists of a complex mixture of solid and liquid particles of organic and inorganic substances suspended in the air. Its major components are sulphate, nitrates, ammonia, sodium chloride, black carbon, mineral dust and water.

PM10 is the fraction of all airborne particles =/< 10 microns (µm) in size, while PM2.5 is the fraction of all airborne particles =/< 2.5µm in size and PM1 is the fraction of all airborne particles =/< 1µm in size (1µm = 1/1000th of a millimetre).

Humans with a sedentary lifestyle typically breathe 15kg of air each day. In highly polluted areas, we breathe more than 25 million particles with each breath.

Mr Dyment concluded: “Using PM1 class filters to a high efficiency rating are best way to protect building occupants in city locations. PM1 could also stand for People Matter 1^st.”