Humidification Issues in ASHRAE Standard

Jeff Boldt, PE, LEED® AP, HBDP and Paul Hansen

Description of the Issues

Humidity control is required in many buildings including healthcare facilities. Many of these facilities have a central boiler plant that produces steam. The most economical humidification system for these buildings is the direct injection of boiler steam into the airstream. The confusion for engineers and code officials is interpreting ASHRAE Standard 62.1 section 5.13, which discusses humidifiers. An excerpt of the relevant sections of the standard is provided below.

5.13 Humidifiers and Water-Spray Systems. Steam and direct evaporation humidifiers, air washers, and other water-spray systems shall be designed in accordance with this section.

5.13.1 Water Quality. Water shall originate directly from a potable source or from a source with equal or better water quality.

This section of the standard is unclear about which common humidification systems are acceptable. For example:

  • When designing humidification systems is it acceptable to inject boiler steam directly into the airstream if it contains any amount of chemicals? As the current standard reads it could be acceptable based on the argument that the boiler steam is originating from a potable water source.
  • Is it acceptable to have a minimum amount of chemicals present in the steam and air if the levels are within the acceptable ranges published by advisory and regulatory groups?
  • If ultra-sonic or spray-type humidification is provided to the space then DI or RO water systems are typically required to provide the ultra-pure water quality. Is this considered "equal or better water quality" since the chlorine has been removed from the water and microbial growth could potentially be present?

Boiler Steam Treatment Chemicals

Boiler steam/condensate systems are subject to corrosion due to the presence of carbon dioxide in the condensate pipes coupled with availability of oxygen and high temperature. CO2 is produced when carbonate and bicarbonate alkalinities in boiler feedwater thermally decompose in the boiler. The carbon dioxide is carried with the steam and then dissolves in the condensate to form carbonic acid, which accelerates corrosion in condensate piping, receivers, and steam traps. If the carbonic acid is not addressed, corrosion will severally damage the entire condensate system and corrosion byproducts can be carried back to the boiler causing additional damage. To minimize condensate system corrosion most central plant boiler systems utilize condensate corrosion inhibiting chemicals called neutralizing amines. Neutralizing amines are volatile alkaline compounds that are added to the boiler feedwater. These amines flash off with the steam and when the steam condenses the amines neutralize the resulting carbonic acid to prevent corrosion in the condensate system.

The three most common neutralizing amines are cyclohexylamine (CHA), morpholine, and diethylaminoethanol (DEAE). These chemicals have been associated with upper respiratory, eye, and skin irritations. Due to this concern the Occupational Safety and Health Administration (OSHA) and the American Conference of Governmental and Industrial Hygienist (ACGIH) have established regulatory and advisory limits for these chemicals. These limits are intended to protect worker safety. These limits are not necessarily appropriate for non-working building occupants since they are based on the 8-hour day as described below.

OSHA has jurisdiction over worker health and safety and publishes permissible exposure limits (PELs) of airborne chemicals that protect workers against the health effects of excessive exposure to hazardous substances. PELs are based on a time weighted average exposure over an 8-hour day and 40-hour week and are enforceable by law.(8) PELs are listed below and can also be viewed at http://www.osha.gov

ACGIH publishes threshold limit values (TLVs), which are guidelines to assist industrial hygienists in making decisions regarding safe levels of exposure to various hazards found in the workspace. TLVs represent the opinion of the scientific community that exposure at or below each TLV does not create an unreasonable risk of disease or injury. Since the ACGIH is only an advisory group their recommendations are not enforceable, but their opinions could be used in legal proceedings. TLV recommendations are lower than PEL requirements for certain amines as shown below in the table.

The Food and Drug Administration (FDA) has established maximum levels of amines allowed in boiler steam that comes in direct contact with food, other than milk and milk products. Chemical treatment companies often use these values as guidelines for the maximum concentrations they will allow each chemical to reach if the boiler steam is currently used for direct injection humidification.

ASHRAE Standard 170 states,

"Steam chemical additives used for humidifiers serving health care facilities shall comply with FDA requirements."
- FDA, 1999 US Dept. of Health and Human Services, Food and Drug Administration in Federal Register 173.310 (April 1999)

The text of the referenced Federal Register is available at
http://www.grokfood.com/regulations/173.310.htm

In our opinion, the wording of Standard 170 is unenforceable, because FDA has no requirements for steam used for humidification.

The limits established by OSHA and ACGIH have changed over the years due to additional research on their health effects. The current limits are listed below.

CHEMICAL OSHA (PELs)8
In Air
ACGIH (TLVs)2,8
In Air
FDA
In Steam
CHA 10 ppm 10 ppm 10 ppm
DEAE 10 ppm 2 ppm 15 ppm
Morpholine 20 ppm 20 ppm 10 ppm

In addition to the established limits for amines described above, amines have an unpleasant odor that can cause complaints. The odor thresholds for these chemicals are listed below.

CHEMICAL ODOR THRESHOLD9
Cyclohexylamine (CHA) 0.90 ppm
DEAE 0.04 ppm
Morpholine 0.14 ppm

We were interested in whether direct-injection of boiler steam containing amines at various concentrations for humidification would cause the amine levels in air to exceed the established limits set by OSHA and ACGIH; and whether this would cause unpleasant odors. Both of these issues should be of concern and addressed in ASHRAE Standard 62.1. Our analysis is shown below.

ASHRAE and other organizations require or recommend that many buildings including health-care facilities be humidified to a minimum of 30% relative humidity. It is also common for equipment manufacturers of diagnostic healthcare equipment to require the rooms to be above 40% relative humidity. Some states, including Illinois, require operating rooms to be above 40% relative humidity. If chemicals are added to the boiler steam as allowed per ASHRAE Standard 170, Ventilation of Health Care Facilities, the maximum levels in the humidified air can be theoretically calculated. Standard 170 states, "Steam chemical additives used for humidifiers serving health care facilities shall comply with FDA requirements." This is somewhat ambiguous since FDA regulates boiler steam that contacts food rather than air, but our attempt to calculate this is shown below for humidification of 100% OA that enters with 0% RH.

Room Air = 73°F DB @ 40% RH. Humidity Ratio = .007 lbs moisture per pound dry air

Equation

The calculation above agrees reasonably well with field studies where amine levels were measured in boiler steam used for humidification and in the room air. Some of the data is listed below for reference.

Amine Steam Amine
Concentrated (ppm)
Airborne Amine
Concentrated (ppm)
Study
DEAE 15 .01 NIOSH
- Cornell University 6
DEAE 5.33 .0024 Unknown : Chemtex Literature 4
CHA 2.93 .008 Unknown : Chemtex Literature 4
Morpholine 19.2 .004 Nalco Research 5
Morpholine 64.8 .018 Nalco Research 5
DEAE 11.6 .010 Nalco Research 5
DEAE 19.8 .031 Nalco Research 5
CHA 30.6 .041 Nalco Research 5
CHA 87.7 .066 Nalco Research 5

 

Based on this theoretical calculation and the field studies we believe that if the amine levels in steam remain below the FDA recommendations for steam in contact with food the chemical concentration levels in the humidified air are well below exposure recommendations by OSHA and ACGIH. However, there is a possibility that the air could contain a high enough concentration of DEAE that it would exceed the odor threshold and thus be objectionable to building occupants. Using the same basic calculation as above we calculated that the maximum concentration of DEAE to remain below the odor threshold is approximately 5.7 ppm.

Please also note that NIOSH completed a study in 1983 at the Johnson Museum of Cornell University. NIOSH investigated complaints of skin and eye irritation by employees. It was determined that the university used a direct-injection steam humidifier and used DEAE for condensate corrosion prevention. After completing air quality testing NIOSH determined the concentration of DEAE in the air was at most 0.01 ppm. While this level was orders of magnitude below any recommended maximum concentrations published by OSHA or ACGIH, they did find DEAE on exposed surfaces. NIOSH concluded that DEAE condensed out of the air and building occupants touched the surfaces, thereby causing the skin irritations and complaints. Thus there is a risk of exposure of amine chemicals to building occupants if the building is not cleaned. In our research we did not find any other cases where this had caused a complaint, however, we have provided this study as additional information for your consideration.

Recommendations and Suggested Wording Options

We recommend that the committee clarify Standard 62.1 as it relates to humidifiers, and that you coordinate the modifications with Standard 170. We also offer the following wording options for you to consider in place of the wording of Standard 62.1 section 5.13.1. These options are in no particular order other than that the first option is the most stringent. The later options are not arranged in order of stringency.

  • Option 1: Water Quality Water entering humidifiers shall originate from one of the following sources and no chemicals shall be added to the water between the source and the airstream.
    • Potable water
    • RO water
    • DI water

Option 1 is the most conservative choice, but increases first costs, maintenance costs, and energy costs.

  • Option 2: Water Quality Water entering humidifiers shall originate from one of the following sources.
    • Potable water
    • RO water
    • DI water

Chemicals and minerals shall not be present in the steam in concentrations that are known to be hazardous to health or that might contribute to an indoor air quality problem. The specific chemicals listed below may be present in steam, but they shall not exceed the following concentrations in the steam.

    • Cyclohexylamine (CHA) : 10 ppm
    • Diethylaminoethanol (DEAE) : 5 ppm
    • Morpholine : 10 ppm

Option 2 is based on the lower of the FDA limits and the calculated value to fall below the odor threshold for DEAE.

  • Option 3: Water Quality Water entering humidifiers shall originate from one of the following sources.
    • Potable water
    • RO water
    • DI water

Chemicals and minerals shall not be present in the steam in concentrations that are known to be hazardous to health or that might contribute to an indoor air quality problem. The specific chemicals listed below may be present in steam, but they shall not exceed the following concentrations in the air in any occupied zone.

    • Cyclohexylamine (CHA) : 0.90 ppm
    • Diethylaminoethanol (DEAE) : 0.04 ppm
    • Morpholine : 0.14 ppm

Option 3 is based on the odor thresholds in air. This is a more direct method than option 2, but is possibly more difficult to measure and would require measurement in many more locations to monitor.

  • Option 4: Water Quality Water entering humidifiers shall originate from one of the following sources.
    • Potable water
    • RO water
    • DI water
    Chemicals and minerals shall not be present in the steam in concentrations that are known to be hazardous to health or that might contribute to an indoor air quality problem. The specific chemicals listed below may be present in steam, but they shall not exceed the following concentrations in the steam or in the air in any occupied zone.
    • Cyclohexylamine (CHA) : 10 ppm steam / 0.90 ppm air
    • Diethylaminoethanol (DEAE) : 5 ppm steam / 0.04 ppm air
    • Morpholine : 10 ppm steam / 0.14 ppm air

Option 4 is based on complying both with the FDA limits and the odor thresholds in air. Proving compliance would require monitoring both steam and air concentrations.

  • Option 5: Water Quality Water entering humidifiers shall originate from one of the following sources.
    • Potable water
    • RO water
    • DI water
      Chemicals and minerals shall not be present in the steam in concentrations that are known to be hazardous to health or that might contribute to an indoor air quality problem. If chemicals are added their concentration in the steam shall not exceed the FDA’s latest concentration limits for steam that contacts food.

Option 5 is similar to Option 2, except that it ignores the odor threshold for DEAE and it does not specifically list chemicals and avoids the need to review the FDA requirements for each new version of Standard 62.1.

  • Option 6: Water Quality Water entering humidifiers that do not boil the water shall originate from one of the following sources.
    • Potable water
    • RO water
    • DI water
      Steam used for humidification shall not have chemicals or minerals present in concentrations that are known to be hazardous to health or that might contribute to an indoor air quality problem. The specific chemicals below may be present in steam, but they shall not exceed the following concentrations in the steam.
    • Cyclohexylamine (CHA) : 10 ppm
    • Diethylaminoethanol (DEAE) : 5 ppm
    • Morpholine : 10 ppm

Option 6 adds the wording "that do not boil the water" in its first sentence. This is based on the premise that the quality of the feedwater to a steam humidifier is irrelevant since the water entering the air will have been distilled. The only chemicals of concern are those that volatilize with the steam. The assumption is that there are few of those that would not be destroyed by the temperature of boiling other than chemicals designed for that purpose. This wording also would allow the use of site-collected rainwater, which would be an excellent source of water with low solids content. We avoided the term "steam humidifier" because of concern that there could be argument that all humidifiers technically create steam.

Final thoughts about testing of amine concentrations:

Testing of steam or condensate amine concentrations is probably easier than testing airborne concentrations, so that has an advantage from the standpoint of compliance and enforcement. Also, testing of the amine concentrations in steam is probably part of most facilities’ existing procedures.

NOTE FOR COMMITTEE:

There is one difference between the version of this proposal that I formally submitted and the versions in this letter. The difference is in the wording of the acceptable waters for humidifiers that do not boil water. I believe that the original wording would not have protected against purified water that was stored long enough to have microorganisms grow to unacceptable levels, such as in an unprotected RO or DI water tank. To protect against this I searched for a standard that that set objective criteria to determine whether water was acceptable and decided that the National Primary Drinking Water Regulations provided an easily referenced set of criteria that are easily accessible. Click here to view them at the EPA's website - http://www.epa.gov/

REFERENCES:

  1. 1. A Guide To Amines In Steam, EHS1007, Garratt Callahan

  2. 2. American Conference of Governmental and Occupational Hygienists http://www.acgih.org/tlv/

  3. 3. Amines, TT-015-0891, Chemtex Corporation http://www.chemtexcorp.com/docarchive/pub/TT-15%20Amines.pdf

  4. 4. Are Neutralizing Amines Safe in Steam Humidification Systems?, Volume 18, Fall 2004, Chemtex Corporation
    http://www.chemtexcorp.com/docarchive/news/Water%20Treatment%20News%2018-NeutralizingAmines%20in%20SteamHumidification.pdf

  5. 5. Grattan, D., Koutek, M., Russum, S., Amine Levels in Steam Humidified Room Air. Engineered Systems, 1989
    https://www.armstronginternational.com/files/products/humidifiers/pdf/techreports/aminelevels.pdf

  6. 6. HETA 83-020-1351, Cornell University,
    http://www.cdc.gov/niosh/hhe/reports/pdfs/1983-0020-1351.pdf

  7. 7. Neutralizing Amine Regulation & Testing, TT-031-1098, Chemtex Corporation
    http://www.chemtexcorp.com/docarchive/pub/TT-31%20Neutralizing%20Amine%20Regulation%20and%20Testing.pdf

  8. 8. OSHA http://www.osha.gov/

  9. 9. Rabinovich, Shulamit, Hospital Steam Humidification Systems and the Chemicals they Use, HPAC Engineering, May, 2004

  10. 10. Regulations Governing Chemical Treatment in Food Processing Plants, TT-012-03900, Chemtex Corporation
    http://www.chemtexcorp.com/docarchive/pub/TT-
    12%20Regulations%20Governing%20Chemical%20Treatment%20in%20Food%20Processing%20Plants.pdf


  11. 11. Steamline Treatment Policy: Humidification, EHS1001, Garratt Callahan

  12. 12. Turpin, J., (2001) Direct Steam Injection Humidification: Is It Safe For Building Occupants?, March, 2001 http://www.esmagazine.com/Articles/Feature_Article/55e590b7ffba8010VgnVCM100000f932a8c0____

 

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