PREMIERE ISSUE

October, 1999

Greetings, Colleague:

I am not sure this was sent to you previously but I thought to
send it again on the off chance that its content would interest
you.  This is the first in a series of technical newsletters
about materials and methods in toxicology, in particular, the
practice of inhalation toxicology.

This first issue is being sent to you because we
know that you have a special interest in the environmental
sciences, toxicology in particular. Should you wish to be removed
from the mailing list, see the note below.

We expect to cover a wide range of topics relating
to general toxicology, aerosol science, animal bioassay, health
risk assessment and respiratory biology. We will try to do this
on a monthly basis and we will archive the documents on our web
site - http://www.inhalation.net

In this first note, we summarize some of the advantages of
directed-flow, nose-only systems:

Q. Why should a directed-flow, nose-only inhalation
system be used instead of a whole-body chamber?

A. There are, in fact, several reasons. Some of these are:
1 - The dose to the lungs can be more readily controlled.
2 - There is greater safety for laboratory personnel.
3 - More animals can be exposed simultaneously under
certain conditions.
4 - A single individual can operate the nose-only system.

More information on the advantages of the nose-only
system as well as diagrams are available at
http://www.inhalation.net.

Choose the publications tab on the opening page.

Another topic of interest is the use of the critical orifice for
flow control.

Q. What is a flow restricting orifice, how does it
control flow and how is it useful in inhalation exposure
sampling?

A.  To hold the sampling flow rate constant, one solution places
a "critical" orifice in the air line leading to a pump
or other vacuum source.  When the air pressure between the pump
and the restricting orifice is less, by a defined ratio, than the
pressure between the orifice and the location sampled, the flow
through the particular size orifice achieves sonic velocity. 
This condition stabilizes the flow rate at a value defined by the
orifice.  Then, flow rate is no longer sensitive to changes in
the downstream pressure. The pressure ratio at any given orifice
size must be maintained at or below the critical ratio (a value
of 0.53 for air) so that the restricted flow rate remains
constant.

More information on this topic is available at
http://www.inhalation.net. Choose the publication tab.

ABOUT CH TECHNOLOGIES (USA) INCORPORATED. 

CH Technologies designs and manufactures a variety of inhalation
toxicology related systems including a patented directed-flow,
nose-only inhalation chamber.  A newly designed cigarette smoking
machine has recently been introduced.  CH technologies equipment
can be viewed at their web site, www.toxics.com.

Questions, comments and requests for additions to our circulation
list may be sent to "jaegerr@idt.net".

REMOVAL FROM OUR MAILING LIST

To be removed from the circulation list, send email to
loppa@bellatlantic.net. Place the word REMOVE in the subject
line.

Rudolph J. Jaeger, PhD, DABT, Publisher of this newsletter
Douglas W. Cooper, PhD, Editor, Technical and Aerosol Sciences
Susan G. Shami, ScD, Editor, Respiratory Biology & Graphics
Coordinator
Arlene L. Weiss, MS, DABT, Editor, Indoor Air Pollution and
Epidemiology