Less than severe worst case accidents Page: 4 of 6
This article is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
Penetration of the system by puncture probes may also defeat the containment integrity,
cause shorting of electrical circuits, allow water penetration that leads to shorts, provide a
conductive pathway for electrical threats or even act as an antennae to attract and conduct
lightning energy into the system.
Thermal
A severe fire will ultimately burn everything to slag and ashes and render a system safe
while lesser thermal environments may create many of the same concerns as mechanical
environments in that they may cause partial breach of a protective container while leaving
the internal system intact and operable. Insulation may be melted and allow shorting,
organic materials may become carbonized and create electrically conductive pathways,
and solder may melt and open some circuits while flowing to complete other circuits. The
electrolyte in batteries can expand due to heating, rupture burst discs, flow into the cells
and produce power.
There are many examples of thermal responses which are actually reversible up to final
destruction. Resistors can heat up and fail to operate, but when cooled can function again.
High explosives can become heated and actually become more sensitive to mechanical
shock initiation while heated or after recooling. Organic materials may have a high
electrical resistivity at benign temperature, undergo a resistance drop as the temperature
rises and then, if the temperature decreases prior to carbonization, the resistance is
recovered as cooling occurs.
There are also examples of thermal activated safing devices which have interesting
responses in less than severe environments. Explosive charges have been incorporated
into circuits to explosively open the circuit in a fire. Some of these can be desensitized
when subjected to heat transients below their initiation threshold so that they don't work
later. Thermal fuses, often made with a solder plug which melts at nominal temperature
thus allowing a spring to open the circuit have been known to open predictably, then melt
further and the molten metal flows back together at higher temperatures prior to final
destruction. Thermal batteries can be heated and produce voltage, and later be reheated
and again produce energy.
While a full raging propellant fire of near 5000 degrees Fahrenheit will quickly destroy
virtually every system, a slow cook fuel fire can allow slow carbonization, pressure buildup,
and material interactions. One such interaction occurs between aluminum and steel. Steel
normally melts at roughly 1850 degrees F, but when the lower melting aluminum comes
into contact with the steel, the materials interact and the steel melts at about 1000 degrees
F.2C4-3
Upcoming Pages
Here’s what’s next.
Search Inside
This article can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Article.
Sanders, Gary A. Less than severe worst case accidents, article, August 1, 1996; Albuquerque, New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc673196/m1/4/: accessed April 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.