Steam Purity is a measure of all contaminants in steam, with high-purity steam containing only trace amounts of contamination. Maintaining high steam purity is important in many industries, but there are few applications where it is more critical than in healthcare facilities that use plant steam for surgical instrument sterilization and/or operating room humidification. In a hospital, any contaminants in the steam could potentially interfere with proper sterilization as well as be inhaled by hospital patients, staff, and visitors. Understanding how and where to add the water treatment chemicals and the factors that can cause boiler water carryover will help hospitals ensure that high-purity plant steam is consistently produced.
Boiler chemical feed and steam purity requirements in hospitals are governed by a combination of ASHRAE1/ASHE2 Standard 170-2017 (Ventilation of Health Care Facilities) and AAMI3 ST79:2017 (Comprehensive Guide to Steam Sterilization and Sterility Assurance in Health Care Facilities).
ASHRAE/ASHE Standard 170-2017 6.6.2 specifies that the additives used in steam systems serving humidifiers in healthcare facilities shall comply with the FDA regulations governing boilers where the steam comes in direct contact with food. The FDA regulations define both the boiler water chemicals that can be used and their maximum concentration. AAMI3 ST79:2017 also states that only FDA-approved boiler additives be used and provides specific recommendations for boiler chemical application and monitoring.
Chemical Feed Location Is Important
Products containing neutralizing amine typically are fed for corrosion control in the condensate system. In the past, it was a generally accepted practice to feed the neutralizing amine product directly to the steam header. However, AAMI ST79 was updated in 2017 with the following guidance:
“Facilities should not add boiler additives or feedwater conditioners to the steam in the steam distribution system”
This guidance was added because feeding the amine product directly to the steam header will cause spikes in the amine level each time the chemical feed pump is activated. These fluctuations in amine level can easily result in the FDA limit of 25 ppm total amine being exceeded while the pump is on. If a sterilizer calls for steam at the same time that the amine feed is active, staining of surgical instrumentation can also result due to high amine levels.
The optimal feed point for neutralizing amines and other treatment products is the storage section of the feedwater tank or deaerator. By adding the treatment chemicals to the feedwater reservoir, they are diluted before they enter each boiler to provide better chemical distribution and more consistent system protection. Because boilers receive treated feedwater in direct proportion to its load, this also allows consistent treatment residuals to be maintained in all operating boilers and eliminates the spikes that occur when concentrated chemicals are added directly to the steam header.
It should also be stressed that hospitals that feed amine products to the steam header are out of compliance with AAMI ST79. When condensate system corrosion cannot be controlled without exceeding FDA-regulated amine levels, a dealkalizer or reverse osmosis system is necessary to reduce the makeup water alkalinity.
Graph showing how the conductivity of a condensed steam sample spikes each time the amine feed pump turns on when added directly to the steam header. The amine level in samples taken during amine feed exceeded the FDA limit of 25 ppm total amine. The horizontal red line shows the conductivity limit established to monitor steam purity in this application.
Amine spikes stopped once the feed location was changed from the steam header to the feedwater tank. Feeding amine to the feedwater tank or deaerator allows for the amine to evenly distribute in the feedwater before it is fed to the boiler resulting in more consistent amine levels in the steam.
Adding Treatment Chemicals Based on % Timer or Feedwater Pump Run Time
Another common practice that can affect steam purity is using a percentage timer or boiler feedwater pump run time to activate the chemical feed pumps.
For boiler systems with on/off feedwater pumps on individual boilers, the feedwater pump run time is only proportional to the steam load under certain conditions. Feedwater pump run time does not necessarily translate into chemical feed requirements when there are changes in the amount of condensate return or mechanical problems that cause the feedwater pump run times to vary. For example, a worn or cavitating impeller, plugged strainers, or restrictions in the feedwater line can cause long feedwater pump run times that result in chemical overfeed. In extreme circumstances, entire drums of chemical can be fed as the result of a malfunctioning feedwater pump.
Adding the treatment chemicals based on percent timer settings can likewise cause problems because the chemical feed rates stay the same regardless of changes in steam load or the amount of condensate returned.
The best method for activating the water treatment chemical feed pumps is in proportion to metered makeup water usage, with all chemicals pumped directly into the storage section of the deaerator or feedwater tank. This results in the even distribution of products and better control of steam purity.
Neutralizing amine is not the only potential source of impurities in steam. Foaming or carryover can also be a significant source of contamination. Condensed steam should have a maximum conductivity of 50 uS/cm in order to minimize the potential of instrument spotting and wet packs in the sterilizers.
High conductivity, excess boiler water alkalinity, rapid changes in demand, and high boiler water levels are common factors that can lead to impurities in the steam due to foaming and/or carryover. The boiler design can also impact the potential for carryover. Monitoring the boiler water conductivity is particularly important in areas where makeup water quality can vary seasonally. In these instances, an automatic blowdown controller is essential.
Understanding how and where to add the water treatment chemicals and the factors that can cause boiler water carryover will help hospitals ensure that high-purity plant steam is consistently produced. This is vital to prevent surgical instrument staining issues and the associated costs due to canceled surgeries. A knowledgeable water treatment partner, like Chem-Aqua, provides value that goes far beyond the chemical program costs. Contact us today!
Written by: Kevin Blake