This technical note aims
at investigating the appropriate helicopter noise metric other than Lmax
to be adopted for evening time criteria for helicopter noise assessment. This exercise covers a critical review of
helicopter noise criteria adopted in Hong Kong and overseas countries, and
international standards. Based on the
results of the review, the recommended noise metric/metrics assessment criteria for
evening period (1900 – 2300 hours) would be adopted in the helicopter noise
assessment of the Environmental Impact Assessment (EIA) Study for Expansion of
Heliport Facilities at Macau Ferry Terminal.
The
study was conducted with the following objectives:
(1) To review
the existing Hong Kong helicopter noise criteria;
(2) To review
the helicopter noise criteria in overseas countries.;
To identify the appropriate noise metric/metrics
other than Lmax with reference to the
review findings on overseas criteria and past research studies.
In Hong Kong, helicopter noise criteria are a guideline as stipulated in the Hong Kong Planning Standard and Guideline until the establishment of Environmental Impact Assessment Ordinance (EIAO). As a Designated Project under the EIAO, the helicopter noise levels are under the control of the statutory requirements. The history of helicopter noise criteria in Hong Kong is de scribed as following paragraphs.
In June 1989, the Government published a major policy
document, the White Paper on 'Pollution in Hong Kong'. The White Paper placed considerable emphasis
on environmental planning, stating that "serious environmental pollution
in Hong Kong is an unfortunate by-product of economic success and population
growth. One of the Government's major
priorities is to halt the decline in environmental conditions and to do more to
improve our environment".
The Hong Kong Planning
Standards and Guidelines (HKPSG) was established in 1991 and Chapter 9 provides
guidance for including environmental considerations in the planning of both
public and private developments. It
applies both to the planning of permanent or temporary uses which will have
potential to cause significant changes to the environment or which are
sensitive to environmental impacts. The
standards and criteria included in the HKPSG will need to be applied with a
degree of flexibility and not in isolation.
But any departure from them should not be accepted without full
consideration of all the implications and the long-term adverse effects on
living conditions in Hong Kong.
As stated in Section 4.2.3
of the HKPSG, night-time operations of helicopters will generally be more
intrusive than daytime operations. For
application in Hong Kong, the helicopter noise is presented in terms of Lmax
dB(A) during daytime period (07:00 – 19:00) and the noise criteria for
residential development and commercial developments are as follows:
Residential Development Lmax 85 dB(A)
OfficeEducational
Institution Lmax
90 dB(A)
Note: The standard applies to the external façade at
operable windows for ventilation of habitable rooms.
Advice from EPD should be sought if it is
anticipated that helicopters will be operated:
(a)
in a
tranquil environment; or
(b)
during
late-evening and night-time.
In 1998, Environmental
Protection Department (EPD) established the EIAO against pollution in the
planning stage of new development projects and proposed residential
developments with a projected population greater than 200,000 to undertake an
environmental impact assessment during planning stage. This statutory provision includes the issue
of helicopter noise. In the EIA stage,
compliance of helicopter noise standards (Lmax) under the HKPSG at
all residential and office facades is required when the proposed project is a
designated project under the EIAO.
However, this noise criterion is applied for daytime period
(07:00-19:00) only.
In considering appropriate evening time criteria for helicopter noise to
be adopted in this EIA Study, review on existing helicopter noise criteria of
overseas countries was carried out, as a guide to the noise levels considered
appropriate in sensitive areas. In
this section, the noise criteria & noise metric of different countries and
international standards for helicopter noise impact is discussed in the
following paragraphs.
The FAA Advisory Circular
Number 150-5020-1, entitled “Noise Assessment Guidelines for New Helicopters
recommends the use of a cumulative noise measure, the 24-hour equivalent sound
level (Leq(24)), so that the relative
contributions of the heliport and other sound sources within the community may
be compared. The Leq(24) is
similar to the Ldh used in assessing the
impacts. The helicopter Leq(24) values
are obtained by logarithmically adding the single-event Sound Exposure Level
(SEL) values over a 24-hour period but without any weighting factors for time periods.
The FAA
recommends exterior noise criteria for individual heliports
based on the types of surrounding land uses.
The following table shows the recommended noise levels.
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Source: FAA Advisory
Circular Number 150-5020-2, 1983
The maximum recommended
cumulative sound level (Leq(24)) from the
operations of helicopters at any new site should not exceed the ambient noise
already present in the community at the site of the proposed heliport.
There are no specified
helicopter noise criteria but it can make reference to the aircraft
criteria. The Ministry of the
Environment assesses the impact of aircraft noise on planned noise sensitive
land uses and the suitability of development. The noise impact assessment is
based on the NEF/NEP contours, approved by Transport Canada.
The NEF rating is based on the Effective Perceived Noise Level (EPNL)
which is given by the Perceived Noise Level (PNL), adjusted for the duration of
fly-over and the presence of discrete tones. The PNL is the maximum perceived
noise level calculated from the third octave band noise levels. The NEF value
is then calculated from the EPNL for each fly-over, the number of fly-overs and
adjustments for day-time and night-time operations. The NEP is similar to the
NEF with the exception that the NEP uses a longer time frame. Neither NEF nor
NEP can be measured directly and can only be calculated from measured
quantities.
The aircraft noise criterion in terms of an NEF/NEP value in any outdoor
area, including the outdoor living area is shown in following table. The criterion
applies to the entire 24-hour period. The distance separation from the airport
and, consequently, the location of the noise sensitive land use with respect to
the NEF/NEP contours, is the only measure that controls the outdoor noise
impact.
|
Time Period |
NEF/NEP |
|
24 hours |
30 |
No standard for
helicopter noise but can make reference to the aircraft noise criteria. In accordance with the provisions of Article
16 of the Basic Environment Law (Law No. 91 of 1993), the environmental
conditions relating to aircraft noise standards are notified as follows.
The standards for regulating the environmental conditions of aircraft noise
(hereinafter referred to as "environmental quality standards") are
established as follows according to Article 9 of the Basic Law for
Environmental Pollution Control and the target dates thereof. The maintenance
of the standards is desirable to preserve the living environment and to
contribute to protecting people's health.
The
values of the environmental quality standards are established for each category
of area shown in following table.
Prefectural governors shall designate the category of area.
|
Category of area |
Standard value (in WECPNL) |
|
I |
70 or less |
|
II |
75 or less |
Note: Area category I refer to areas used exclusively for residential
purpose and Area category II refers to other areas where the normal living
conditions shall be preserved.
The values of the environmental quality standards above are
measured and evaluated by the following method.
(1) Peak levels of aircraft noise, which is higher than background noise
level by 10 dB or more, and the number of such aircraft, shall be recorded in
dB (A) for, in principle, for seven consecutive days.
(2)
Measurements shall be carried out outdoors and at points selected as
representing the points of aircraft noise in the area concerned.
(3) The
timing of measurements shall be chosen as representing the duration of aircraft
noise at the point of measurements, taking into consideration the flight
conditions and meteorological conditions including wind directions.
(4) The
aircraft noise shall be evaluated as follows. The WECPNL values for each day
will be calculated from peak levels of aircraft noise and numbers recorded
under subparagraph (1) using the following equation. The energy mean of daily
WECPNL values is used to calculate the noise level in question.
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Note: dB(A) stands for the energy mean of all peak levels of any one
day, and N stands for a value calculated by the following equation: N = N2 +
3N3 + 10(N1 + N4), where N1 is the number of aircraft between 0:00 a.m. and
7:00 a.m., N2 the number between 7:00 a.m. and 7:00 p.m., N3 the number between
7:00 p.m. and 10:00 p.m., and N4 the number between 10:00 p.m. and 12:00 p.m.
(5) Anyone of the following instruments can be used for measurement: the
sound level meter provided for in Japan Industrial Standards C-1502, precision
sound level meter under International Electric Standards Conference Pub/179, or
any other equivalent instrument. In these cases, A-weighted calibration and
slow dynamic response shall be used.
The environmental quality standards shall not be applied to areas around
airports where there are 10 or less daily landings and take-offs and to those around
airports in remote islands.
There are no specified noise criteria for helicopter noise. The
helicopter noise impact will be evaluated in assessing based on the same
standards as for aircraft noise.
According to Anabeim General
Plan/Zoning Code, the maximum recommended cumulative sound level Leq(24)
from the operations of helicopters at any new site should not exceed the
ambient noise already present in the community at the site of the proposed
heliport.
The exterior noise criteria
for individual heliports based on the types of surrounding land uses. The following table shows the recommended
noise levels.
Normally Compatible
Community Sound Levels
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Type of Area |
Lt 24 |
Residential
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Suburban |
57 |
|
Urban |
67 |
|
City |
72 |
|
Commercial |
72 |
|
Industrial |
77 |
The noise impacts of
helicopter operations were based on the cumulative noise exposure of multiple
operations over daily periods. The
noise method that was utilized was Day-Night Average Sound Level (DNL),
Ldn. This noise metric was based on
social survey research that was conducted over the years to quantify people’s
reaction to noise exposure levels in the community. It divides 24 hours into two time periods: day (0700 – 2200) and
night (2200 – 0700). For events that
occur during the night time hours, a night penalty of 10dB is added to take
into account the greater sensitivity of people to sounds that occur during
these time periods.
The DNL noise results
range from 65 dB DNL to 68 dB DNL by measuring noise levels for the background
ambient around San Francisco general hospital.
An annual average of DNLs
is used by the Federal Aviation Administration to describe airport noise
exposure. Areas with noise impacts less
than 65dB DNL are considered “compatible” with residential use; areas at or
above 65dB DNL are designated “incompatible” with residential use.
For night time noise,
between the hours of 22000
– 0700, an additional 10 decibels is added to compensate for sleep interference
and other disruptions caused by night time noise.
For noise assessment,
equivalent sound level (Leq) correlates well and can be combined
with other types of noise analyses such as Composite Noise Rating, Community
Noise Equivalent Level and day-night noise levels characterized by Ldn
where an Leq(24) is measured and 10dB(A) is added to all noise
levels measured between 2200 – 0700.
These different types of noise analyses basically combine noise
measurements into measures of cumulative noise exposure and may weight noise
occurring at different times by adding decibels to the actual decibel level.
In California, noise
levels are described using the Community Noise Equivalent Level (CNEL)
metric. The terminology is the same as
the DNL except that it includes a 4.77 dB penalty for each aircraft event that
occurs between 1900 – 2200, and a 10 dB penalty for each aircraft event that
occurs between 2200 – 0700.
In year 1978, The Federal
Government via the FAA established a noise threshold which it thought residents
should be expected to tolerate, the
threshold level was set at 65 DNL. It
was agreed that if the DNL exceeded 65 dB, the airport operator or local
government could implement mitigation procedures such as buying out residents living within the 65
DNL contour, or sound proof the owner’s home. The Environmental Protection Agency (EPA) argued
that for people’s health
and peace of mind, the threshold should be set lower, 55 DNL. However, the aircraft technology at that time
could not achieve better
performance that 65 DNL, and the Government knew that it they used a lower threshold
, it would have to spend
hundreds of billions of dollars to solve the noise problem at the receivers. After
that, the American National Standards Institute (ANSI) codified the threshold
levels for human activities, the
standard specified that threshold
above 65 DNL is incompatible with residential living.
There is no restriction for helicopter noise but a
control plan including noise criteria would be established for individual
project. Followings are some examples
of the project relating to the helicopter.
Night time criteria,
which offers to provide noise insulation grants to homes near located military
airfields which are exposed to significant night time flying (2300 – 0700) and
which are subject to recurring maximum sound levels (defined as greater than 20
movements) of 82dB(A) or greater.
Night time rotary wing
criteria, which offers to provide noise insulation grants to homes located near
military airfields which are exposed to significant night time flying (2300 –
0700) and which are subject to this nightly average sound level.
Recommended Noise Exposure Categories for New Dwellings Near Existing
Noise Sources under this project is as follows:
|
Noise Levels
Corresponding to the Noise Exposure Categories for New Dwellings LAeq, T
dB |
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Noise Exposure Category
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Noise Source
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A |
B |
C |
D |
|
Air Traffic 0700–2300 hrs 2300–0700 hrs |
<57 <48 |
57 – 66 48 – 57 |
66 – 72 57 – 66 |
>72 >66 |
Key to Noise Categories
(NEC)
A Noise need
not be considered as a determining factor in granting planning permission,
although the noise level at the high end of the category should not be regarded
as a desirable level
B Noise should
be taken into account when determining planning applications and, where
appropriate, conditions imposed to ensure an adequate level of protection
against noise.
C Planning
permission should not normally be granted.
Where it is considered that permission should be given, for example
because there are no alternative quieter sites available, conditions should be
imposed to ensure a commensurate level of protection against noise.
D Planning permission should normally be refused.
New
Plymouth District Plan
A set of helicopter noise standard is proposed for the
helicopters operating from helicopter landing areas under this project. The maximum noise levels, measured at any
point within the boundary of any receiving site within the residential
environmental area or measured at the notional boundary within the rural
environment area should not be higher than Ldn 50 dB(A) when day-night average
sound level over any period of 5 consecutive days or maximum noise levels and
its Lmax should not be higher 70 dB(A) on any day between 10 pm to 7 am the
following day.