This guideline is to share the information with the Construction Industry on the use of Hydraulic Concrete Crusher (HCC) for demolition works and on the implications of its use based on the experience gained in the trial use of HCC in a number of Housing Authority (HA) projects.

In an attempt to address the problems of frequent public complaints about excessive noise nuisances from HA demolition sites, the HA initiated studies, with advice kindly given from the Environmental Protection Department (EPD), to find out ways to minimize these nuisances to nearby Noise Sensitive Receivers (NSRs). The use of HCC was recommended for further investigation and trials had been conducted in some selected projects. The findings from these trials gave very encouraging results in noise reduction during demolition processes. This guideline summarizes experience gained and results obtained from these trials with a view to providing project teams with useful information on the use of HCC in demolition projects.

Statutory Requirements on Noise Control
Although currently there is no statutory requirement on the permissible maximum noise level emitted from a demolition site, the HA specification does impose a maximum noise limit according to an EPD's advisory document, Practice Notes to Professional Persons (ProPECC) PN 2/93, issued in May 1993. The maximum noise levels specified in the HA's Standard Specifications were developed based on this ProPECC. (Appendix 1)

Currently, the most popular mechanical plant used in demolition works is the excavator mounted Hydraulic Breaker (HB). Since the operation principle of HB is by percussive striking actions of its chisels, the sound power level for HB can be as high as about 122 . If the noise level reduction is purely relied on distance attenuation, it may require about 84 to 93 metres in order to reduce to a level of 75 . For two HBs working at the same time, the distance required may be up to 120 to 130 metres.
 

Specification Requirement
In the current HA specification, there are two main procedures to control the noise emitted from a demolition project:

	1.	Noise Control Regulations
		The contractor is required to comply with noise limits as prescribed by the Noise Control Ordinance.
	2.	Equipment noise level limits
		It specifies the noise level generated from equipment and tools used should not exceed:
		(a)	Leq of 75  if the ambient noise level < 70 ;
		(b)	5  above the ambient noise level if it is > 70 ; or
		(c)	Leq of 70  during normal school hours if the NSR is a school.
		Usually, the duration of measurement is 30 minutes.

General
To reduce the noise nuisance during the demolition works, the following methods can be considered:

Use of Quieter Plants and Equipments
There are various quieter plants, equipments or methods available for demolition works, such as HCC, saw-cutting, chain-cutting, high-pressure water jet and expansive chemicals. However, apart from HCC, the others are only practical in small-scale demolition works.
 

Use of Acoustic Enclosures
Noises from a demolition process are mainly airborne and structural borne. It is rather difficult to minimize the structural borne noise (from the vibration of the machinery and the building elements). The airborne noise is comparatively easier to handle. Using acoustic enclosure is one of the ways, which includes:

	1.	Enclosure for the HB The most common method is using an enclosure for the HB. At present, some HBs in the market claim to be designed to lower sound power levels (10 ) than ordinary HBs and / or made with materials with higher noise damping factors such as "Incramute". Some of them are with built-in acoustic enclosures, such as the brands "Krupp" and "Rammer". There are also excavators with lower noise level than ordinary ones and with a reasonable cost. The other method is by fixing noise-damping sheets onto the booms of the excavator. However, it is not very cost effective.
	2.	Enclosure for the plant / working area This method is being adopted in some other countries to enclose the whole working area by acoustic enclosures. The method is very expensive and given the site constraints commonly encountered in Hong Kong, it is considered not practical.

Other Methods
There are other various noise reduction methods, but they are also impractical for the use at construction sites. One example of these methods is the "active" method by using out-phased noises to counter-reduce the noise emitted and combinations of different demolition methods to be used together. Another example is the saw-cutting method to cut the building into larger pieces and transport them to ground level by crane. HCC or crusher will then be used to break them into smaller sizes.
 

The use of HCC is at present the most practical and economical demolition method, with its low noise emission and effectiveness having been verified in previous trials. This method provides a practical solution if the predicted noise level at nearby NSRs will be exceeded by using traditional HB.

What is HCC?
Both HB and HCC are excavator mounted mechanical tools for demolition works. The action of HCC is by the opening and closing of its jaws to crush concrete, powered by the hydraulic fluid supplied by the excavator. For details, please refer to Appendix 2. The main noise source from HCC is from the excavator itself. Noises created by HCC and its crushing actions are very low and can be negligible in noise assessment. Currently, the supply of HCC in Hong Kong is limited and requires a delivery time of about one month. HCC is commonly used in other countries and there are wide ranges of types and suppliers of HCC from most construction plant manufacturers (Appendix 2).
 

Findings and Observations

	1.	Effective in noise reduction Noise measurement results from all previous trials demonstrated that noises emitted from HCC were significantly lower than the conventional HB. In the trial project at Lam Tin, four noise stations were established during the demolition works. Noise measurements had been made throughout the whole demolition process. The results agreed quite well with the Technical Memorandum on Noise from Construction Works Other Than Percussive Piling issued by the EPD (Appendix 1). The sound power level of the HCC was about 110  and the HB was about 120 . (In the Technical Memorandum, the figures were 112  and 122  respectively.) Table 1 shows some comparisons between HB and HCC.   Table 1: Summary of Noise Level measured between HCC and HB   Station Background Noise Level Noise Level of HCC Working   (5 min)   Noise Level of HB Working   (5 min)   Increase in Noise Level by HCC Increased in Noise Level by HB A 61.9 63.8 71.3 1.9 9.4 B 62.0 66.3 74.1 4.3 12.1 C 62.0 68.8 75.8 6.8 13.8 D 62.4 65.7 72.8 3.3 10.4
	2.	Lower working efficiency The demolition rate of HCC is about 50% slower than that of HB due to the time required in locating HCC in the right position, the opening of the jaws and the crushing action. Basing on past experience in demolition projects, using the traditional HB requires about three days to demolish one floor of a typical HA's residential block of size 17 x 100 square metres. The efficiency is therefore about 567 m / Day. Basing on the trials, the efficiency level of HCC is in the range of 270 to 340 m / Day. Basing on the maximum output of HCC, i.e. 340 m / Day, the time required for these two types of plants is calculated and listed in the Table 2. It can serve as a useful reference for project teams to determine the contract period in case they consider the use of HCC. Table 2: Comparison of Demolition Time between HCC and  HB   No. of Storeys Demolition by HB (Day) Demolition by HCC (Day) Additional Time Required (Day) 7 21 35 14 12 36 60 24 16 48 80 32 20 60 100 40
		(Assuming to demolish a 17m x 100m typical residential block)
	3.	Maintenance of plant The maintenance of HCC is similar to that of HB. Most of the HCCs are as durable as HB. The hydraulic part of HCC is similar to that of HB and therefore maintenance requirements would be similar. Although the moving parts of HCC are more than those of HB, the maintenance technique is simple and can be provided by the supplier.
	4.	Limitation of HCC There are occasions on which it would be difficult to start the crushing actions, such as at the start of each level and in areas where the "jaws" of HCC cannot reach both sides of the elements to be demolished.
	5.	Assistance of other plants The assistance of an excavator mounted HB and / or a back-toe is required under some circumstances to enhance the efficiency. The use of HB for the said purpose was adopted in the trial projects and its use was limited to 12:00 noon - 1:00 pm with prior agreement with site staff in order to minimize the nuisance created.

Safety Precautionary Measures
These trial projects only involved demolition of seven-storey high residential blocks and therefore structural member sizes were less than 450 millimetres in width / thickness. HCCs used were not heavy duty and the weight of excavator used could be as low as 12 tonnes. However, if a larger size HCC is required for thicker member sizes, the excavator mounted has to be much heavier. This is because the excavator has to provide sufficient hydraulic fluid for the operation of HCC and to act as a counter-weight for HCC. It is therefore necessary to select the suitable HCCs for the demolition works at the planning stage by considering:

Cost and Time

Although the use of HCC can solve most of the problems in noise nuisance created during demolition works, it is necessary to consider the following before specifying the use of HCC in demolition contracts.
 

Time and Cost

Need
Since the use of HCC will increase both the contract sum and the contract time, before deciding to use HCC, it is worthwhile to consider the following:

	1.	Will the noise level exceed the specification? (Carry out a noise level estimation on the closest NSR using the method specified in the TM (Appendix 1), assuming HB has SPL = 122 ). In case the blocks are with considerable floor area, more than one HB may be used.
	2.	In case the predicted noise level exceeds the allowable limits, can quieter type HB (those with acoustic enclosures) be used instead of HCC?
	3.	Apart from HCC, are there any other feasible methods that can be used to reduce the noise impact? For example, can demolition works be carried out on school holidays? Or can the demolition sequence be planned to make use of existing blocks as noise barriers, etc.?
	4.	Can the project allow the additional time and cost for using HCC?
	5.	Will there be any other benefits and considerations in using HCC, for example, reduced vibration and improved public images, etc.?

Appendix 1: Regulatory Ordinance, Regulations and Practice Notes

Appendix 2: Common Types of HCC
There is a wide range of suppliers of different types of HCC. In the selection of the suitable HCC, it is necessary to consider:

	1.	The minimum weight of the carrier excavator;
	2.	The maximum jaw opening size (maximum member size < 0.7x maximum jaw opening is recommended); and
	3.	HCC with the 360 rotation function.

Brand	Mantovani Benne	Brokk	NPK	Sango	Atlas Copco
Model	CR5	CC 620	S-15X	TS500RCD	HCC 550
Made	Italy	Sweden	Japan	Japan	Sweden
Carrier Weight (ton)	5 - 14	4	10 - 18	6 - 11	5 - 14
Weight (kg)	520	480	1410	550	570
Output (ton)	50	45	70	40	-
Working Pressure (bar)	200 - 250	250	210	210	150 - 250
Oil Flow (l/min)	50 - 90	60 - 120	80 - 150	-	50 - 90
Max. Opening Width (mm)	450	620	750	500	450
360 Rotation	Yes	Yes	Yes	Yes	Yes

Appendix 3

Photo 1: Common types of HCC	Photo 2: Common types of HCC	Photo 3: HCC used in the Valley Road Trial	Photo 4: HCC used in the Lam Tin Pilot Project