Michael Holliday ac017 at FreeNet.Carleton.CA
Sun Feb 22 07:42:16 EST 1998

"R Williams" (force4 at onlink.net) writes:
> what are unsafe levels of amonia indoors and when could you tell when levels
> are unsafe
> Richard

Estimated LC values for human exposure to ammonia:

Exposure (minutes)      LC50 (ppm)      LC10 (ppm)

     120                 3,700           1,900
      60                 5,300           2,600
      30                 7,500           3,800
      10                13,000           6,600
       5                19,000           9,400
       2                30,000          15,000

Give or take factors of two or so.

DISCLAIMER (which appeared in the source identified below):  It 
cannot be emphasized enough that these dose-lethality values are 
based on few data and considerable speculation -- they should be 
used predictively only with appropriate circumspection.

Source:  Engelhardt, F.R. and Holliday, M.G., "Dose-lethality
         Relationships of Acute Exposure to Anhydrous Ammonia",
         Report No. INFO-0153.  Ottawa, Ont.: Atomic Energy
         Control Board (1 March 1985).

And, if memory serves, the ACGIH TLV(R) is 25 ppm.

The odour threshold is of the order of 10 ppm and, I am assured on 
good authority, concentrations above 400 or 500 ppm cause 
noticeable discomfort in the genital area (especially if one is 
hot and sweaty :-).  Of all mammals, bats seem the most resistant 
to ammonia and appear to tolerate atmospheric concentrations of 3000 
to 5000 ppm without adverse effects.

Michael Holliday
Ottawa, CANADA

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