Welcome to the NavList Message Boards.


A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Add Images & Files
    Re: Artificial horizons and mercury
    From: Peter Ifland
    Date: 2003 Jul 20, 12:50 -0400

    What follows is a lift from
    http://acc6.its.brooklyn.cuny.edu/~scintech/mercury/WhatBigDeal.htm .
    [m^3 means cubic meter]
    "VC = S-Q   [I think this equation is a little fuzzy]
    Where V is the room volume in cubic meters (m^3), C is the
    concentration in micrograms per hour, and Q is the air flow
    rate from the room in m^3. S, the mercury evaporation rate,
    is the rate of mercury vaporization per unit area of
    mercury. This is a constant value of 7 ug/cm^2/hour at
    The Agency for Toxic Substances and Disease Registry
    (ASTDR)'s minimal risk level (MRL) for mercury vapor
    inhalation is .3 ug/m^3. This is an estimate of the daily
    human exposure that will most likely not result in risk. The
    occupational exposure limit set by the U.S. National
    Institute for Occupational Safety and Health is 50 ug/m^3."
    Here's a simple example, use a 6 cm X 10 cm mercury horizon
    for one hour in a 5m X 5m X 4m room at 20 degrees C with a 2
    m^3 per hour ventilation.
    The mercury lost from the horizon equals (7 ug/cm^2/hr) X
    (6cm X 10cm)             =420 ug/hr into a (5 X 5 X 4m) room
    with a 2 m^3/hour turnover of air
             = 420 ug/hr /(100-2) m^3 = 4.2ug/m^3/hr.
    If left for 12 hours, the concentration builds to 50.4
    ug/m^3 , i.e.. the occupational exposure limit.
    Conclusion: Keep the mercury container in a sealed flask
    indoors, fill and use the horizon outdoors. If you inhaled
    ALL of the evaporation of mercury from a 6cm X 10 cm horizon
    for six minutes out of every hour while taking sights, you
    would still not exceed the occupational limits. Thus,
    personal exposure will be well within safe limits.
    Did I get it right?
    Peter Ifland
    P.S. Thanks to Paul Hirose for pointing us to a very
    informative site.

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.

    Email Settings

    Posting Code:

    Custom Index

    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site