I am currently searching for a portable dehumidifier but notice that most of them come with a indicator that actually using the Blue Silica Gel, which I believe that it may contain Cobalt Chloride.

So, I would like to ask,
(1) if that is the case, would the portable dehumidifier become a harmful product?
(2) would an Orange Silica Gel contain other harmful chemical that is currently not found?


I had a poke around in an effort to determine the dye used in orange silica gel and was able to find two material safety datasheets (MSDSes) for orange silica gels which both gave different empirical formulae for the dye ($\ce{C25H30ClN3}$ and $\ce{C20H14O4}$), which suggests that there are multiple formulations of orange/yellow silica gel. Both of these dyes are organic molecules (as opposed to transition metal salts), and now their possible identities are given at the bottom of this response. Suffice to say that orange silica gels were designed specifically to avoid the use of cobalt chloride, which is fairly toxic.

As a document1 from the US National Parks Service indicates, the chief danger of cobalt chloride is its environmental toxicity if it enters soil or water through improper disposal. Cobalt salts are often rather evil, and this is actually reflected in the name, which is ostensibly an alteration of 'kobold'. However as long as the beads are kept in a suitable enclosure such as a filtered dessicator plug, they should not present a hazard. Inhalation of dust from the silica gel beads, direct handling of beads or cobalt chloride-impregnated materials or complete inundation of the dessicant (which could dissolve some of the cobalt chloride) are three possible ways the cobalt chloride could present a direct hazard, but the disposal of blue silica gel-containing products in landfill and subsequent leaching of cobalt chloride is probably the chief concern.

As far as the orange beads go, as I was not able to determine the specific indicator molecule(s) I can't ascertain their toxicity, suffice to say that they are by design less harmful than cobalt chloride and appear to be generally considered safe under normal use.

P.S. (finally, after chrome crashing multiple times)

F'x points out that $\ce{[C25H30N3]^{+}Cl^{-}}$ is crystal violet, which is not super toxic but for which there is evidence of carcinogenicity2 and which is considered an environmental pollutant.

$\ce{C20H14O4}$ may very well be phenolphthalein, which is considered to be a carcinogen by some authorities, most notably appearing on the California Prop. 65 listing3.

I guess the idea is that cobalt chloride is less desirable than either of these dyes. Don't eat the beads, and wash your hands!

(1) U.S. National Park Service; Cobalt Indicating Silica Gel Health and Safety Update; 2005, pp. 1-3

(2) Littlefield, N.A.; Blackwell, B.-N.; Hewitt, C.C.; Gaylor, D.w.; Chronic toxicity and carcinogenicity studies of gentian violet in mice; Fundamental and Applied Toxicology, 2004, pp. 902-912

(3) Chemicals Known to the state to cause cancer or reproductive toxicity; State of California EPA; March 16 2012, p. 17

  • $\begingroup$ Wikipedia says “An alternative indicator is methyl violet which is orange when dry and green when hydrated”. Isn't that simply it? $\endgroup$
    – F'x
    May 21 '12 at 10:05
  • $\begingroup$ @F'x - Yeah I noticed that C25H30ClN3 is the empirical formula of crystal violet but didn't mention it because, well, it's typically violet. Additionally, C20H14O4 could be phenolphthalein, but that's violet as well! I'll add that. $\endgroup$ May 21 '12 at 10:15
  • $\begingroup$ Wrt. toxicity: 1. Wikipedia says: "antibacterial, antifungal, and anthelmintic properties" (and has a link to a proper paper). This implies that it is toxic for quite a number of organisms. 2. It is used as (non-toxic) DNA dye. I.e. it does stain DNA, but cells do not (immediately) die from that. While this does not imply carcinogeneity, it shouldn't be too surprising, either. $\endgroup$ May 21 '12 at 13:48
  • $\begingroup$ @cbeleites - Hi, I can't access the referred paper and there's no abstract available. Ref. 2 in my answer points to a paper that indicates that crystal violet is carcinogenic in mice. As always, the medicinal use of substances such as crystal violet and phenolphthalein go to show that there are many degrees of carcinogenicity and that substances can have markedly different acute and chronic toxicities. $\endgroup$ May 21 '12 at 14:12
  • $\begingroup$ @RichardTerrett, Hi Richard, It good to hear that "as long as the beads are kept in a suitable enclosure such as a filtered dessicator plug, they should not present a hazard." from a expert like you. Now, I can feel safe when buying a portable dehumidifier. $\endgroup$
    – Jack
    May 22 '12 at 0:48

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