Pierre River Mine Project

AIR AENV SIRS 6 – 14
Section 11.1
Risk management requires that the criticality of the failure be considered. This
requires that both the probability and the consequence of failure be considered
jointly. A piece of equipment that fails frequently but whose failure carries little
consequence poses a low risk. On the other hand, equipment that has a low
frequency of failure but whose failure has serious consequences is a high risk
management issue. In the response to this SIR 250d, Shell acknowledges that
there is a potential to create concentrations sufficient to cause acute injury to
vegetation.
13a Discuss potential human health effects as a result of accidental releases of SO2.
Provide quantitative evidence in support of the discussion.
Response 13a The health assessment for this upset scenario was included in EIA, Volume 3,
Appendix 3-8, Section 4.3.3.
Question No. 14
As part of the health assessment, maximum predicted ground-level air
concentrations of SO2 were compared to varying concentrations at which health
effects are known to occur. As discussed, the aim of the health assessment was to
establish the nature and severity of the health effects related to the predicted air
concentrations associated with the described upset events.
The findings of the health assessment indicated that some of the predicted SO2
concentrations were high enough to potentially cause adverse health effects.
However, Shell has committed to redundant SO2 pollution control equipment that
will switch to natural gas within 15 minutes and, consequently, decrease the
exposure time.
Request Volume 2, SIR 235a, Page 20-2.
Shell indicates The typical odour threshold for each compound was determined
by calculating the geometric mean of the available odour thresholds. It is
common practice in sensory evaluation to use geometric means as they account
for the wide range of responses over several orders if magnitude. The SIR
response then demonstrates the calculation of an H2S threshold using the
maximum and minimum values from the 9 pieces of cited literature. The
calculation assumes that all of the reported H2S odour thresholds in the cited
references are equally valid in calculating the geometric mean. Many of the
references Shell cites for odour thresholds are outdated and not appropriate for
the objective of assessing the effects of odour. More recent sources of
information provide confirmation of much lower odour thresholds for H2S (e.g.,
Harvard University 2005 1 ; Iowa State University 2004 2 ; Lenntech 2006 3 ). All of
these sources confirm an odour threshold of 1 ppb for H 2 S. The use of the
geometric mean concentration value of 14 µg/m 3 underestimates H2S odour
impacts due to the proposed development knowing that there are observation
data to demonstrate that H2S is detectable at instantaneous odour concentrations
April 2010 Shell Canada Limited 11-13
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