Corrosive Airborne Contaminants
Corrosive airborne contaminants and other negative environmental factors (such as abnormal temperature and humidity) may expose IT equipment to higher risks of corrosive failure. This article specifies the limitation on corrosive airborne contaminants with an aim at avoiding such risks.
Table 7-3 lists common corrosive airborne contaminants and their sources.
Symbol |
Sources |
|---|---|
H2S |
Geothermal emissions, microbiological activities, fossil fuel processing, wood rot, sewage treatment |
SO2, SO3 |
Coal combustion, petroleum products, automobile emissions, ore smelting, sulfuric acid manufacture |
S |
Foundries, sulfur manufacture, volcanoes |
HF |
Fertilizer manufacture, aluminum manufacture, ceramics manufacture, steel manufacture, electronics device manufacture |
NOX |
Automobile emissions, fossil fuel combustion, chemical industry |
NH3 |
Microbiological activities, sewage, fertilizer manufacture, geothermal emissions, refrigeration equipment |
C |
Incomplete combustion (aerosol constituent), foundry |
CO |
Combustion, automobile emissions, microbiological activities, tree rot |
Cl2, ClO2 |
Chlorine manufacture, aluminum manufacture, zinc manufacture, refuse decomposition |
HCl |
Automobile emissions, combustion, forest fire, oceanic processes, polymer combustion |
HBr, HI |
Automobile emissions |
O3 |
Atmospheric photochemical processes mainly involving nitrogen oxides and oxygenated hydrocarbons |
CNHN |
Automobile emissions, animal waste, sewage, tree rot |
Organosilicon, organotin |
Chemical plant, rubber plant, paint or ink containing organosilicon |
The concentration level of corrosive airborne contaminants in a data center should meet the requirements listed in the white paper entitled Gaseous and Particulate Contamination Guidelines for Data Centers published in 2011 by the American Society of Heating, Refrigerating and Air-conditioning Engineers (ASHRAE) Technical Committee (TC) 9.9.
According to the Guidelines, corrosive airborne contaminants in a data center should meet the following requirements:
- Copper corrosion rate
Less than 300 Å/month per ANSI/ISA-71.04-1985 severity level G1.
- Silver corrosion rate
Less than 200 Å/month.
Å, or angstrom, is a unit of length. One Å is equal to 1/10,000,000,000 meter.
According to ANSI/ISA-71.04-1985 Environmental Conditions for Process Measurement and Control Systems: Airborne Contaminants, the gaseous corrosivity levels are G1 (mild), G2 (moderate), G3 (harsh), and GX (severe), as described in Table 7-4.
Severity Level |
Copper Reactivity Level |
Description |
|---|---|---|
G1 (mild) |
300 Å/month |
An environment sufficiently well-controlled such that corrosion is not a factor in determining equipment reliability. |
G2 (moderate) |
300 Å/month to 1000 Å/month |
An environment in which the effects of corrosion are measurable and may be a factor in determining equipment reliability. |
G3 (harsh) |
1000 Å/month to 2000 Å/month |
An environment in which there is high probability that corrosion will occur. |
GX (severe) |
> 2000 Å/month |
An environment in which only specially designed and packaged equipment would be expected to survive. |
See Table 7-5 for the copper and silver corrosion rate requirements.
Group |
Gas |
Unit |
Concentration |
|---|---|---|---|
Group A |
H2S |
ppba |
< 3 |
SO2 |
ppb |
< 10 |
|
Cl2 |
ppb |
< 1 |
|
NO2 |
ppb |
< 50 |
|
Group B |
HF |
ppb |
< 1 |
NH3 |
ppb |
< 500 |
|
O3 |
ppb |
< 2 |
|
a: Part per billion (ppb) is the number of units of mass of a contaminant per billion units of total mass. |
|||
Group A and group B are common gas groups in a data center. The concentration limits of group A or group B that correspond to copper reactivity level G1 are calculated based on the premise that relative humidity in the data center is lower than 50% and that the gases in the group interact with each other. A 10% of increase in the relative humidity will heighten the gaseous corrosivity level by 1.
Corrosion is not determined by a single factor, but by comprehensive environmental factors such as temperature, relative humidity, corrosive airborne contaminants, and ventilation. Any of the environmental factors may affect the gaseous corrosivity level. Therefore, the concentration limitation values specified in the previous table are for reference only.