Examination of Witnesses (Questions 7040
- 7059)
7040. At that stage, was the Crossrail route
being safeguarded?
(Mr Methold) I would imagine it was, yes.
7041. Thank you very much. That is all I wanted
to ask by way of re-examination.
7042. Chairman: Mr Methold, there are
one or two things. You referred, when you were taking about noise
reduction, to the Thames link and Jubilee line extension about
the hardware and that you could not understand why it had not
been included as it was 100per cent available. Can you elaborate
a little bit on that?
(Mr Methold) Can you repeat that?
7043. Chairman: You were talking about
the hardware put together for the building of the Jubilee line
extension and the Thames Link, all the noise reduction standards,
that the hardware which had been prepared for the construction
was fully available.
(Mr Methold) I think my reference to the hardware
was in relation to whether a preferred design of a L90-5 could
be achieved by the Crossrail project.
7044. Chairman: Can you elaborate on
that a little bit because if there is something available it might
be helpful to the Committee and that is why I am interested?
A.(Mr Methold) Absolutely. What
we have had to do to understand whether an L90-5 was achievable
for Crossrail was to understand what Crossrail had assumed would
be the level of reduction inside the ventilation shaft as part
of their environmental statement work. They gave a fairly detailed
report giving us the predicted noise levels that they had from
their ventilation shafts but nothing about what was inside the
shafts. Some internet searching on our behalf revealed a report
which gave us the sound power levels and the assumed level of
attenuation inside the ventilation shafts. From that point we
were then able to work out the additional attenuation that was
required. To step back slightly, there are two types of mitigation
that can be applied to ventilation shafts. One we call an "in-line
attenuator". Essentially it is placed in front of the coaxial
fan, the fans that are blowing the air through the shaft. It is
made with an absorbent material and it lets the air flow through
it but at the same time it absorbs the noise, in very simple terms.
We know that the Promoter assumed an attenuator that is three
metres long, which is a reasonably hefty unit. We have found that
they do not need to have any more than an extra metre and a half
on top of that to achieve L90-5 across all of their ventilation
shafts. That is not an enormous extra amount of—
7045. Sticking with that, you also referred
in questioning to the costs that might be attributed to doing
that in these sections. You gave a figure, less labour costs,
of about £100,000. Is that just pie in the sky? Do you have
any analysis?
(Mr Methold) I do have analysis. We contacted
the supplier that we know Crossrail used to generate their noise
source terms and their attenuation performance, the very same
supplier, and we had costs from them on a per square metre basis.
I am hoping that is consistent with the budget that the Promoter
has in place.
7046. Could you prepare a note on that and get
back to the Committee, but only in respect of that which we just
discussed there, not for the whole of the Crossrail project?
(Mr Methold) Certainly. Just to add to that,
the reason we looked a the cost analysis on the
vent shafts only was because the Promoter was
making the point that it was the main reason
they could not accommodate the Thameslink 2000
L90-5 design criterion.
7047. On the question on scientific evidence
which Mr Taylor put to you on at least three occasions, I never
heard an answer. Albeit you said at one point that there have
been complaints at a oneper cent increase and that indicated that
there was a problem, you never really answered his question as
to whether there was any scientific evidence of fact that it did
have that effect.
(Mr Methold) In so far as it was a logged complaint
at the local authority from a resident.
7048. I understand where you are going, but
his question to you was: Has there been any evidence which showed
conclusively that that was a fact or not or was it still a matter
that was conjecture and which has not been established yet?
(Mr Methold) Certainly there is a noise assessment
done by specialist acoustic consultants in that case and a report
was produced which indicated that that complainant was likely
to be experiencing L90+1.
7049. You would hold that as fact?
(Mr Methold) I would, yes. That was a report
7050. Could you supply the Committee with a
copy of that?
(Mr Methold) Certainly.
Chairman: Thank you.
The witness withdrew
Mr Rupert Thornely-Taylor, Recalled
Examined by Mr Taylor
7051. Mr Thornely-Taylor is well known to the
Committee. I will not introduce him again. What is the objective
of the National Planning Policy so far as development that has
the potential to cause noise is concerned?
(Mr Thornely-Taylor) It is contained in paragraph
10 of PPG24 which we have already looked at. In a nutshell, it
is that there should not be an unacceptable degree of disturbance.
7052. What does the National Planning Policy
say in regard to reducing existing ambient noise levels?
(Mr Thornely-Taylor) PPG24 has no section devoted
to reducing existing ambient noise levels.
7053. What does the National Planning Policy
say with regard to meeting the guidelines for community noise
levels set out in the document published by the WHO?
(Mr Thornely-Taylor) The only place you find
reference to the WHO material in PPG24 is where it explains how
it derives its system for categorising new residential development
according to its noise exposure category. That is all.
7054. We have seen from PPG24, paragraph 10
(page 72 in document A75) the reference to: "Much of the
development which is necessary for the creation of jobs and the
construction and improvement of essential infrastructure will
generate noise. The planning system should not place unjustifiable
obstacles in the way of such development."[75]
If a design target is set by reference to the absolute levels
set out in the guidelines for the Crossrail fixed installations,
what do you say about practicability of design to that sort of
target?
(Mr Thornely-Taylor) One has to
take a different view by day and by night. By day in some locations
it would be a major engineering obstacle to achieve the levels
and would place an unjustifiable obstacle in the way of development.
In other ways, at night time the WHO levels are nothing like good
enough because they use the whole eight-hour night period as the
averaging time and since the fans we are talking about may run
for only a few minutes in a night, you could in fact have a fan
making a noise well up into the 50s and still not exceed the WHO
figure of 45. From that point of view, they are very unhelpful.
I really think they are a bit of a red herring in the present
circumstances because the WHO document is all about transportation
noise sources and nowhere in the document do they address noise
from fixed plant. It is by extension that people such as Mr Methold
seek to apply them to fixed plant. They were never intended for
that purpose.
7055. In the context of National Planning Policy
indication that the development should not cause an unacceptable
degree of disturbance, how do you see a design criterion of background
plus 5 dB in BS4142?
(Mr Thornely-Taylor) It fully complies with
the requirements of PPG24 and it certainly achieves the objective
of not causing an unacceptable degree of disturbance and it is
implementable and practicable and shown to work well on previous
projects.
7056. You heard the point that was made earlier
on this morning that if the plus 5 criterion is adopted, the nominated
undertaker will simply design to that so as just to meet that
level. In the light of the paragraph to which I drew Mr Methold's
attention in the draft IP, paragraph 2.12, what do you have to
say to the Committee about that suggestion?[76]
(Mr Thornely-Taylor) Most certainly
that will not happen because, as we saw in the draft IP, paragraph
2.12: "While a degree of attenuation required is site dependant,
not least because of different levels of background noise at different
sites, the nominated undertaker will be required to use reasonable
endeavours when designing the shafts to reduce the noise below
the assessment criterion where it is practicable to do so."
And, as Mr Methold has said, Crossrail have provided information
to Havering which shows that there are many cases where it is
entirely practicable to do that and many of the shafts will improve
on the Crossrail policy and it certainly will not be an upper
limit which a contractor will just achieve at every single site.
It will be a limit that we need to meet at the severe engineering
constraints at a few of the most difficult sites.
7057. Chairman: Mr Taylor, we have to do our
duty. We will return in 20 minutes.
The Committee suspended from 2.59 pm to
3.12 pm for a division in the House
7058. Mr Taylor: Mr Thornely-Taylor, what scientific
evidence is there that a minus 5 dB criterion would result in
material benefit to the amenity of those who might otherwise be
affected by noise from fixed installations compared to a plus
5 dB criterion?
(Mr Thornely-Taylor) On this particular
topic I already mentioned the fact that most noise targets are
about transportation noise for which there is information about
the relationship between the number of people, a noise and the
levels, but for fixed plant we do not have that kind of scientific
evidence. In general, one can say if noise levels are sufficiently
satisfactory to avoid an unacceptable effect, then there is no
advantage in going below a noise level.
7059. If the plus 5 dB design criterion is adopted,
what can you tell the Committee about the prospects of meeting
that criterion in terms of the mitigation that is available?
(Mr Thornely-Taylor) It does present some severe
engineering challenges. The Committee did receive a slightly over-favourable
impression from Mr Methold's evidence. The noise levels we are
talking about are low and after incorporation of the fan noise
attenuators that were referred to, the dominant noise source is
just aerodynamic noise of the air coming out of the louvres of
the ventilation shaft. Mr Methold talked about bolting another
metre of attenuator on but you cannot bolt an attenuator on the
outside of the louvres of a vent shaft and that is the kind of
thing which is the reason why there are engineering difficulties,
which admittedly can be reduced at a cost somewhere along the
line, but they are the top-line concern that we must take into
account when considering this policy.
75 Crossrail Ref: P75, Planning Policy Guidance 24:
Planning and Noise, Development Control, Noisy Development (HAVGLB-14704-072). Back
76
Crossrail Ref: P75, draft Information Paper, Noise from Fixed
Installations (HAVGLB-14704-120). Back
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