ASHRAE Journal - April 2023 - 56

REFRIGERATION APPLICATIONS
COLUMN
Andy Pearson
Nontoxic?
BY ANDY PEARSON, PH.D., C.ENG., FELLOW ASHRAE
I have been delving into the art of risk assessment for industrial refrigeration systems
and unearthed some surprising and interesting quirks. Here are a few anomalies that
help keep the daily workload interesting. I preface this column with a disclaimer that
I am not suggesting that we abandon safe working practices-just sayin'.
The international standard ISO 817:2014 recognizes
two classes of refrigerant toxicity, described in clause
6.1.2 of the standard as " lower chronic toxicity " (class
A) and " higher chronic toxicity " (class B). ASHRAE
Standard 34-2022 defines toxicity as " the ability of
a refrigerant to be harmful or lethal due to acute or
chronic exposure by contact, inhalation or ingestion "
and goes on to say " For this standard, temporary discomfort
at a level that is not impairing is excluded. " ISO
817 doesn't have a definition of toxicity but it
does define acute toxicity as " adverse health
effect(s) from a single short-term exposure "
and chronic toxicity as " adverse health
effect(s) from long-term repeated exposures. "
The puzzle is that study of cause and effect
in dozens of documented serious industrial
refrigeration accidents showed that when
fatal accidents occur with ammonia the casualties
are almost always within a few feet of
the point of release. However, the traditional methods
of analyzing the consequences of ammonia releases
don't seem to acknowledge this and use calculation
techniques more suited to other chemical hazards.
Looking more deeply into references on ammonia toxicity,
I found that there are no chronic toxic effects and
the threshold level for serious permanent injury from
inhalation was more than 1,500 ppm. So why would it
be classed as " higher chronic toxicity " by ISO 817?
The threshold limit value (TLV) for long term exposure
to ammonia is low because it has such an irritating
reaction with moist body parts (eyes, nose, throat) that
the occupational exposure limit (OEL) is therefore typically
set in workplace regulations as 25 ppm. This value
assigns it to class B in ISO 817, but this has nothing to do
with toxicity; it is what Standard 34 calls " temporary
56
ASHRAE JOURNAL ashrae.o rg
A P R I L 2023
Refrigerant classification is
complicated.
discomfort at a level that is not impairing, " an effect
supposedly excluded from the classification process.
This reminded me of my favorite refrigerant safety
joke (credit to Professor Joachim " Joe " Paul, former head
of IIR's Science and Technology Council): Joe was a great
proponent of the use of water as a refrigerant in vapor
compression systems, but he always gave the stern
warning that water was obviously the most hazardous
refrigerant " because it's the only one that contains
sharks. " There is a serious point behind Joe's
quip: the assessment of risk has to be relevant
to the circumstances. Suitable metrics
and methods need to be used, otherwise the
conclusions reached will be inappropriate
and possibly even counter-productive.
In the case of ammonia risk assessments,
the client needs to be clear about the objective.
Worker safety should be paramount
and leads to a number of key requirements
in training, managing and equipping staff. Comfort and
convenience for the surrounding community is also a
relevant objective but requires a different set of measures
and is not really a safety concern; it is more about
being a good neighbor. Measures that ensure neighbor
comfort will not guarantee worker safety and vice versa.
I worked on this puzzle with Alex Pachai, chair of the
IIR's Safety Working Group and Kent Anderson, former
president of IIAR, following a safety workshop held a
year ago at the IIR's Cold Chain conference. We hope to
present the findings in a series of papers in Paris later
this year. Meanwhile, ISO 817 is currently being revised
and the anomaly about chronic toxicity mentioned
above will hopefully be resolved.
Andy Pearson, Ph.D., C.Eng., is group managing director at Star Refrigeration in
Glasgow, UK.
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ASHRAE Journal - April 2023

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