Question about humidity

[TPring]

Is there an optimal/acceptable range for humidity [in relation to coins]? I am assuming less is better.


I keep my better coins in a safe and in that safe is an electronic hygrometer [to measure the air moisture] and, upon opening the safe, it usually reads in the mid-to-upper 50's [55-58].


I have three different methods of trying to reduce the moisture: an electric element (that came with the safe), moisture-absorbing beads and, a bowl of rice. However, I have noticed on a few occasions where the sensor reading actually dropped a couple of points after opening the safe.


Any suggestions/comments?


Thanks,

[mustbebob]

I think that the 55-58 reading is fine for your coin storage. You are correct in that lower is better but the condensation can get to be an issue in the 60-70% range. Something as simple as the rice and/or desiccant will not hurt anything either. When the reading drops a few points upon opening the safe, it is just showing that the humidity level in your room was lower at the time you opened the safe. The humidity just equalizes... that's all.

[jfines69]

The desiccant beads should be sufficient... Even tho rice is suppose to be dry my experience is that rice retains some moisture normally below 5%!!!

[TPring]

Thank you for the replies -- That's a measure of comfort.


Now, the fact that the humidity actually drops after opening the door has me baffled. With the three methods at work in the safe, I should think that it should be lower inside and the humidity reading should actually rise after opening the door.


Any thoughts?

[mustbebob]

The only way to measure that is to measure the humidity both in and out of the safe independently. Without knowing the humidity in the room, we can only assume which one is higher or lower.

[jfines69]

Any time you open the safe out side air enters... That air is still there when you close it up... Keeping the dehydrators fresh should also help... Also very few safes are completely air/water tight those type of safes are normally special made...Hope that helps a little!!!

[TPring]

The only way to measure that is to measure the humidity both in and out of the safe independently.

There in lies the conundrum, the humidity reading is about 55 in the area where the safe is kept but, inside the safe the reading is even higher [even with three preventative measures].

[jfines69]

There in lies the conundrum, the humidity reading is about 55 in the area where the safe is kept but, inside the safe the reading is even higher [even with three preventative measures].

Have you tried removing the rice???

[mustbebob]

There in lies the conundrum, the humidity reading is about 55 in the area where the safe is kept but, inside the safe the reading is even higher [even with three preventative measures].

Without ever having gone to meteorology school, I would say that relatively stagnant air in the safe would tend to hold more moisture than the room where the air can circulate. I think in this case, the percentage is so minimal that it really isn't an issue.

[silver1985]

This topic can get confusing if there isn't any distinction between humidity and relative humidity.
Most instruments measure relative humidity.

One example that is most explanatory to me, is that if you open a quart jar in Las Vegas when the temperature is 114 deg and the relative humidity is 5%, and then put a lid on it tightly, and take it to the north pole, or your freezer, (i.e. lower the temperature of the contents) the relative humidity in the jar would probably read close to 100%.

Thus, You have to be consistent when your compare the different conditions and changes in the results by the instrumentation of "inside and outside" the vault.

Therefore: If the "relative" humidity drops in the vault when you open the vault, that suggests that the air temperature in the vault increases. The reasoning that the air temperature could/would rise when the vault door is opened, would be supported, if the vault was sitting on a cool concrete floor. Does this represent your experience?

[Petespockets55]

Good info on humidity vs. relative humidity.

[VAB2013]

Good info on humidity vs. relative humidity.

Just be glad you are not in Alabama today, it just rained a little bit then the scorching sun came back... it's like 105 in the shade .... but the good news is, I saw a few leaves falling in the wind (probably couldn't stand the heat)

[TPring]

Have you tried removing the rice???

Not yet. In fact, I only put in the rice after the other two methods were not effective.

[TPring]

... The reasoning that the air temperature could/would rise when the vault door is opened, would be supported, if the vault was sitting on a cool concrete floor. Does this represent your experience?

It does -- It is mounted on a concrete slab.


Thanks for that explanation.

[ray_parkhurst]

Keep in mind that dessicants need maintenance, or they can actually cause problems by increasing the RH. A bowl of rice or a silicon based absorber will absorb moisture to a certain extent, somewhat independent of RH, and if the temperature drops they can release moisture back into the environment of the closed safe. The electric element simply stabilizes the temperature, ensuring it never gets cold and thus maintaining low RH. Anyway, key to ensuring low RH is to replace the dessicants often so they don't cause more problems than they are worth.