[General Discussion] Reclassified confined spaces, desiccants, ultra-low humidity
I'm open to opinions and thoughts here.
We have a reclassified confined space that we pump HEPA filtered, indoor, temperature-controlled air into the space (from a port on one side of the CS out of the access port other side) while people are working. The air conditioning and HEPA filtration are only for added comfort. This makes the confined space more comfortable, but the volume of the cold air really masks how much workers are sweating while working, because the sweat dries quickly, even at relative humidity between 25-50%
Recently, someone in the organization suggested that we further filter the air through a desiccant, to bring the relative humidity of the air forced through the reclassified space down to <1%.
I've done some research on ultra-low humidity environments in places like clean rooms, but haven't come across much data for quantitative thresholds relevant to low, or ultra-low relative humidity work environments. I've read some studies that outlined symptoms of dehydration like dry skin, and in extreme cases, bloody noses as potential hazards. Is anyone aware of other physiological hazards outside of what has already been listed?
From a standards perspective, I've been unable to find any relative humidity requirements for general industry, or construction standards.
Comments (9)
The only thought I had at first was that if you don't have an industry guidance because your situation is unique, be extremely cautious. 1. changing the equation can be dangerous in general when working in that kind of space. 2. doing what you propose my cause unforeseen individual health issues unless you have at an length understanding of the health status of the individuals in the space. If you can't find guidance to the proposed scenario, my policy is to back it up to where it was, where we CAN have guidance or an acceptable level of risk everything else being equal.
I know of know regulatory guidance regulations or requirements on humidity. I would agree with what Kevin says above, and wait with eager anticipation to see what Dr. Hinton might offer to the conversation.
If I was still unsure, and I was in your shoes, I would consider calling either or both of my friends for further guidance. One is an Occupational Health Board Certified DO (= to an MD) with many years of experience in Occ. Medicine. The other is a CIH with over 40 years of IH experience. He also has a MS in Bio-Chemistry and actually had 2 years of Med School, before he decided IH was a better career move.
In So Cal you got have some resources like that! Interesting question!
I am having trouble understanding the benefits of bring the humidity down that low. If you are already concerned about workers not realizing how much they sweat, bringing the humidity down will make this problem worse. Plus, low humidity like this will also increase the insensible loss of fluid (moisture lost through breathing) because the inhaled air will remove moisture from the respiratory track.
Out West, in the summertime, we often see humidities below 20%. When this happens, you need to drink more fluid to stay hydrated.
Lower humidy vs. higher humidity has its trade offs. With lower humidity, it allows the moisture to evaporate more efficiently, which in turn, cools the body off quicker. On the other hand, when it's super humid (like here in Kentucky where our relative humidity in the summer runs around 80% or higher), you still sweat, but the sweat doesn't evaporate as easily, so it limits your body's ability to properly cool off because their clothes will just be absorbing and holding the moisture. The higher humidity is often uncomfortable, so people naturally want to take more breaks anyway (if properly trained).
In general, I've always heard that worker's feel comfortable when the relative humidity is 30%-50%, so I would say that the RH you have right now (<50% RH) is acceptable as long as the employees don't complain too much about it. I'm not sure of the ambient temperature inside this space, so if the temperature is high (let's say >85°F), then the low humidity might make it difficult for them to detect heat-related illnesses. If the ambient temperature is <80°F or so (generally speaking), then they may be ok.
Do you know what the actual RH is inside the space when the mechanical ventilation is operating?
ANSI/ASHRAE Standard 55: Thermal Environmental Conditions for Human Occupancy is for indoor occupancies but may provide some guidance on your issue. Also, if there is any flammable liquid transfer involved in the space, then the low humidity can cause static buildup leading to fires or explosions.