ASHRAE Journal - June 2019 - 72

COLUMN REFRIGERATION APPLICATIONS
Andy Pearson

A Design for Life
BY ANDY PEARSON, PH.D., C.ENG., FELLOW ASHRAE

After an incident or accident there seems to be no end to the people willing to step
up and offer an opinion on just where exactly things went wrong. Engineers have
a relentless desire to understand things better and I regularly tell my staff that it is
smart to learn from your mistakes, but smarter to learn from someone else's.
few minutes later, the slow ﬂow of oil had ﬁnished and
This can be healthy but can also create problems; particularly in our litigation-rich environment.
was replaced by a high velocity jet of much less viscous
When the incident or accident has happened it usuammonia. This had blown the hose out of the barrel and
ally is, on the face of it, caused by human error at the
the contents of the high pressure receiver were being
time of the accident. Oftentimes, there needs to have
emptied onto the ﬂoor. Of course, the hose had not
been multiple errors before the disaster can occur, but
been tied to the barrel. The mechanic entered the room
these should not be viewed as independent COULD THE DESIGNER HAVE DONE BETTER? without any face mask or other respirachance events. If one mistake creates the
tory protection. The ammonia content in
circumstances for another, and goes uncorthe air at head level was apparently low
rected, then it is really only a matter of time
enough to be tolerable, but when he bent
before the next domino falls, and so it condown to close the shut-off valve with his
tinues until the tragedy is complete.
adjustable wrench he inhaled the much
Consider for example a fatal accident that occurred
higher concentration at ﬂoor level and keeled over.
about ﬁfteen years ago. A mechanic was tasked with
Clearly, the mechanic carried a lot of responsibildraining oil from the shell side of a refrigerant-cooled
ity for his mistakes but with more foresight he would
oil cooler on an ammonia cold store plant. The drain
never have been put in that position in the ﬁrst place.
point on the bottom of the shell & tube oil cooler had a
The designer should have speciﬁed that the drain point
capped shut-off valve but no spring-loaded safety valve,
would be ﬁtted with a spring-loaded valve and should
despite the fact that these had been required by code
also have ensured that the liquid line valve was in an
in the jurisdiction for many years. The justiﬁcation for
accessible location. The installation crew should not
the omission was that this was not a point from which
have been permitted to put that valve in a place conveoil was usually drained. There were shut-off valves in
nient to them but of no use in practice-it was probably
the refrigerant liquid pipe leading down from the high
installed when the whole room was scaffolded, hence
pressure receiver and the gas pipe leading back there
its unreachable location. Recognizing the previous failbut while the valve in the gas pipe was at ﬂoor level
ings, site management should have ensured that suitthe one in the liquid line was 20 ft (6 m) in the air with
able access was provided, either by insisting the valve
no way of accessing it. The longest ladder on site was
was relocated, or by providing a permanent access
apparently only 10 ft (3 m) and this had been the situaplatform or at the very least by buying a ladder that was
tion for many years. There was no ammonia alarm syslong enough to reach. Finally, rather than tasking the
tem in the machinery room and not much ventilation.
mechanic with oil draining on his own while also fulﬁllThe mechanic connected a hose to the shut-off valve and ing other duties, he should have been given assistance
ran it into a barrel. He removed the seal cap, opened
and a clear schedule to ensure that the oil drain was
the shut-off valve with an adjustable wrench, checked
never left unattended.
that oil was slowly ﬂowing to the barrel and then left
Andy Pearson, Ph.D., C.Eng., is group managing director at Star Refrigeration in Glasgow, UK.
the room to attend to other duties. When he returned a
72

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ASHRAE Journal - June 2019

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