ISA Standard

ISA S71.04-1985	OnGuard Correlation	Effects
Class GX >2000 Å/30 Days	Class GX >66 Å/24 Hours	Electronic/electrical equipment not expected to survive due to corrosive attack.
Class G3 <2000 Å/30 Days	Class G3 <66 Å/24 Hours	High probability that corrosive attack will occur. Probable effect on equipment reliability in less than 5 years.
Class G2 <1000 Å/30 Days	Class G2 <33 Å/24 Hours	Effects of corrosion are measurable and are a factor in equipment reliability. Possible effects in less than 5 years.
Class G1 <300 Å/30 Days	Class G1 <10 Å/24 Hours	Corrosion is not a factor in determining equipment reliability.

Most computer equipment manufacturers cite the ISA Standard for acceptable levels of airborne contaminants, ISA-S71.04-1985 "Environmental Conditions for Process Measurement and Control Systems: Airborne Contaminants". Because the OnGuard's measurements correlate directly to this Standard and provide real-time data, many manufacturers, like Honeywell and ABB, reference the OnGuard in their literature and discuss the importance of monitoring the environment.

From Honeywell: "Monitoring the environment is a must in the control rooms. Purafil's OnGuard real-time monitoring is the preferred method of monitoring because coupon testing can only give a 30-day or 90-day average."

From ABB Automation: "Installation of OnGuard Continuous Corrosion Transmitters (CCTs) should be considered for real-time measurement of the environment and trended on the DCS system. These CCTs should also be mounted in the Winder Inverter room as well as the QCS rack room."