Some steam humidifiers used the main heating plant steam for humidification.  Concerns have been raised over the treatment chemicals getting into the airstream. (Some think the level of chemicals is negligible but I personally have not investigated the issue).
An alternative may be to have a steam to steam humidifier where your water source is clean (Reverse osmosis water for example)

It is quite common to use "clean-steam" generators.  As Walkes says, they can be powered in different ways - including using the existing steam in a steam-to-steam heat exchange process.  Complete packages are readily available from humidifier mfrs.  Ideally, these should be fed with DI water, which is often available in a health care or laboratory environment.

Typical boiler water treatment is not something you'd want blasting into the airstream on a regular basis.

I have seen maintenance organizations disconnect humidification systems completely - rather than make them work.  Adequate attention to protective limits and dependable controls has been an issue in times past.  The first time a steam valve sticks open on direct injectors within ductwork is eye-opening, to say the least.  The reaction was often to disconnect the system entirely.

Yet, if the winter outside air quantities are great enough, it becomes physically impossible to maintain healthy relative humidities (>30%) without humidification.

Many thanks for you comments.

In particular with regard to the chemical treatment - very good point, one that didn't occur to me.

Thnaks again

With a proper water treatment program, there shouldn't be any boiler chemicals carried over with the steam. Any water treatment company I know of offers food grade chemical programs, and they're typically not much more expensive than the standard ones - maybe 10%. There are processes in large food plants where direct contact steam is used for cooking - rice steamers come to mind. There are lots of steam to water mixing stations for wash-up hoses as well, and I don't know of any health problems associated with workers who are routinely exposed to far higher levels of steam in the air than pretty much anybody else.

Personally, I'm far more concerned about water-born issues than ones from steam.

With respect, what you suggest is the exception, not the rule.  Campus or industrial environments may have very little direct connection in the management between the boiler additives and the end users in a particular building.  If a particular building or plant was built with this feature in mind from the outset, perhaps - but that is not the norm.

There is also the issue of what develops in the pipe systems -  heavy metal exposure and/or plasticizers in plastic pipe, etc.  I don't necessarily agree with it either, but the fact is, those things are becoming concerns these days.  There's just not a good reason to expose people to that unless you've designed the plant from the very beginning with regard to those issues.

A good reference check is to ask yourself, "Is this steam condensable to potable quality?"  If not, clean, segregated steam generation is the safest thing to recommend in the general case unless you're certain.

If the steam plant crew can't look after their water treatment program, it sounds like more of a management issue than a technical one.

Heavy metals in steam lines? From ordinary carbon steel pipe? How so? Plastic pipe (or anything) in steam service? Not for long...

There were several deaths Legionairs disease in an insitution this fall, in Toronto. The problem was traced to drift from a cooling tower. I've seen the goo that can accumulate in water humidifiers - they have their own sets of issues. The chimps that can't properly maintain steam equipment don't necessarily do a better job with water.

The PVC was a general comment about water contamination.  The crud and rust that develops in CS pipe and MI fittings, CI pumps, strainers and other devices is obvious.  Even so, similar materials are used to connect cleam steam generators and their grids - even plastic/rubber hoses.  The question of contaminants is one of volume and years of collected "goo", as you say, and/or chemicals from treatment in the system's infrastructure.

The point is, as an Engineer designing for humidification in a building, you cannot be too sure of the chemical treatment used by the boiler technicians - especially long-term.  You may have the luxury of an entire heat utility based on food-contact purity steam, the rest of us do not.  In campus or plant environments, the installation of a few humidifiers is not going to dictate the chemical treatment of an entire heating plant.

On the other hand, the water and Legionella comments are puzzling.  The subject of the thread is steam humidifiers.  Clean steam generators may use clean water (DI is best) as a source, but steam is produced.  If that's an issue for microbial growth, then a lot of autoclave mfrs have a problem.

My chimps have clean steam.  The mice and other animals do, too.  The people demand no less.

I second Tombmech on this issue. Clean steam is generally used in pharmaceutical plants. Usage of chemicals in the steam require us to validate the product for the absence of the chemical or its insignificant on the stability of the product. This is difficult and more time consuming.

ISPE guideline says the steam should be as clean as the air into which it is injected. Though this is a tricky guideline, it is presumed that they are speaking about clean steam with condensate quality equivalent to WFI.

Is there any data at all regarding the "hidden dangers of steam humidifiers"? We've done work at a tobacco processing plant that is kept as humid as any indoor swimming pool area, by steam humidifiers. I'm not aware of any health problems related to the anything, except perhaps the actual product. There's a pretty militant union in this operation - if there was any question of a health issue from the humidification system, they'd be all over it.

There's possibly rust in condensate return lines. There should be NO rust in steam lines. If you've got rust in steam lines, that means they're not sloped/trapped correctly. Rust in steam lines means there are piping layout issues.

Using cleansteam for a healthcare facility is an overkill.It is a huge investment as well.If the steam quality is really suspect,go for a local electric humdifier which generates its own steam without any chemical additives.

On a diffrent note if you look through the Health Technical Memorandum(HTM) which governs the design of hospitals in the UK,HEPA filtration is not mandatory for the HVAC system in operation theatres.

Hmmm ... interesting opinions.  I would only point out that there is a direction toward goodness, and a direction away from it.  Sometimes how far in that direction one goes is determined by economics, and by weighing the alternatives.  It doesn't change which direction one must choose for goodness, though.

TBP, if we're dueling projects, I've put 20,000 #/hr of raw, boiler steam directly into a 300,000 cfm airstream for an aircraft paint booth.  However, that's a process application, with limited long-term exposure to the occupants.  Sometimes, they're even on breathing air.  Similar to your tobacco example: exposure to isocyanates, toluene, MEK, or worse put direct steam humidification in its proper context.

I've also put in many dozens of Liebert units with direct steam humidifiers, with no clean-steam segregation.  Again, that's for a process - with limited occupant exposure (and ventilation) compared to the internal load.

Both of those decisions were economic ones - based on the context of the systems, exposures, and type of occupants in the project.  Again, please refer to the subject line, "Steam Humidifiers - Health Care."

It does sound like you are blessed with unusually clean steam, and steel pipe that never rusts.  In the deep south where I live, rust appears on anything ferric within a day or two - whether it's used for clean steam or not.

As for SAK9's opinions on the matter, I can't explain them.  He doesn't want to use HEPA filtration, either - so what good does it do to argue the merits of clean steam?  We each make our own professional judgments.  Disagreement is certain to happen.

Thanks again tombmech,

My colleges and myself are under the same opinion as yourself. We have had further advice from the supplier of direct steam injection units - they are unable to gaurantee there will be no chemicals from steam plant carried over to steam injected into airstream (even with two seperators).

This has now been passed onto the Consultant and Client for their review and proposed alternative action (electric steam humidification).

Many thanks again

Using direct steam injection, you have to the following concerns:

For service to areas with patients with respitory problems this not really recommended.

You have to research the boiler plant chemicals utilized in the facility. There are some compounds that use amines to maintain pH levels in the condensate network. These amines are carcinogenic.

Humidification is required for OR's, radiology (cat scan, nuclear med, xray, mammo, etc because the equipment requires a min RH), areas using 100% OSA, and other areas in the AIA guidelines or where required by the AHJ.

I would highly suggest a stainless steel section fore/aft the humidifier absorption distance. G90 doesn't cut it.

Thanks cme,

The maintenance/service will not be an issue, as these are/were proposed to be installed in the duct work within the plant room - easy access.

The actual use of the direct injection and possible problems has been handed over to the infectios disease department at the hospital for their input.

It looks like they will go for stand alone units (electric with RO water), rather than use the existing steam plant.

Thanks for all the other comments, it has been greatly appreciated.

Why would any operation permit the use of amines for steam plant water treatment in an setting such as this? There are long proven pretreatment technologies available.

I'm reminded of an article in a trade magazine I saw a while ago. A smaller breakfast cereal plant (steam directly on their product) had worries about boiler water treatment chemicals getting onto their product. The article trumpeted their installation of a steam filtering device to deal with this perceived problem. (Mind you, there was no indication whatsoever of any problem.) The article continued, saying how the plant religiously inspected this filter monthly, as part of their PM program. It was always clean, though - no need to change anything. But the plant management all felt better, knowing that this device was in place. From what I read, the only people who should be "feeling better" are the people who sold this device - and the feeling should be directed towards their bank account, rather than any perceived public health benefit. All the food company did, was spend $100,000 to solve a problem that never existed in the first place.

I recall reading about a high pressure mist water system that does not use steam.