Articles & Case Studies


Posted: Thursday 5th March 2009

A major fire at a Candle factory on the Blandford Heights Industrial Estate, in Blandford, Dorset, UK gave rise to a serious sewer network problem for Wessex Water, the regional water company responsible for services to this part of the country.

The fire, at temperatures of up to 1000oC, caused stored candle wax and the containers in which it was contained, to melt and flow freely into the main drainage system serving the industrial estate. This network comprised largely 150 mm and 225 mm diameter clay and concrete pipes. Unfortunately once clear of the raging fire, the wax and melted plastics cooled and reverted to their usual solid form. This caused serious blockages in the drainage network including the gravity section taking run-off from the factory area itself, a pumping station which transferred flows towards the local treatment works and the rising main out of the pump station. The wax flow remained liquid long enough to flow through the gravity pipes into the pump station, to fill the pump station almost to capacity thereby activating the pumps which pushed melted wax into the rising main before it solidified sufficiently to almost totally block the system.

The job of removing the wax from the sewer network fell to engineers Julian Britton and Mark Harris of the Wessex Water Critical Sewers Team (WWCST), part of Wessex Engineering Construction (WEC). After carefully considering the options available, WWCST called in main contractor Barleymans Environmental Services of Cubley Common, Derbyshire, to undertake the task of removing the wax and other detritus created by the fire out of the sewer system.

Barleymans is a long established family business with a staff that can boast a combined experience of over 100 years in the jetting and tanker business. As time has moved on so has Barleymans, keeping abreast of technology and equipment to ensure the company can handle the most demanding of jobs. This was just such a job.


Subsequent to the fire, some 500 m of drainage system, varying between 150 mm and 225 mm diameter was found to be between 50% and 75% restricted by solid wax. Being relatively small diameter drains this meant the available drainage capacity serving much of the industrial estate was severely limited. With the pumping station also effectively out of action, it too being filled with wax, Wessex required a speedy and effective clean up at the earliest possible time. In the meantime, the main issue was to keep the industrial estate’s drainage flowing by use of over-pumping to ensure that disruption to the remaining businesses on the industrial estate was kept to a minimum.


To this end, Barleymans brought in some heavy-weight equipment in the form of its Weirdermann Recycler Super 1000 tanker/jetter unit to clean out the effected pipelines.

In just five working days using the tanker/jetter unit Barleymans managed to completely clear some 300 m of the gravity sewer pipes.

Barleymans then turned to opening up the pumping station. For this part of the work the contractor utilised a hired compressor and small hand jack hammer to pick out the solid wax from the pumping well. In total, the wax removed almost filled an 8 yd3 skip set up on site to remove the waste material.

More recently, Barleymens went back to try to complete the cleaning of a further 60 m length and a 27 m section of the concrete pipe that had previously proved difficult to clean using the original jetting technology. This time the contractor brought in, from Holland, a ‘hot box’ which allowed the use of high temperature water (100oC) at flow rates of 86 gpm (390 l/min) at 140 bar pressure to be used to remove the wax remaining in the pipe, by melting it out as much as jetting it. The new system was effective over the first 27 m length of the pipe, which took only 2½ hours to complete. A final solution to reopening the final +60 m section of this pipe was still under consideration at the time of writing. Attention was then turned to the rising main section leading off the pumping station. This part of the works was handed over to specialist high pressure jetting contractor.


The rising main comprised a 150 mm diameter PVCu pipe. Originally, when the jetting specialist attempted high pressure jetting to complete this part of the work, attempts to clear the pipe using the jetting technology were not completely successful and there was concern that further attempts might cause significant material damage to the plastic pipe.

This was when WWCST approached ClearView Surveys Ltd to see if there was another solution to the problem.

Clearview Surveys is an experienced Dorset based Wessex Water Framework Contractor which runs a variety of mainline CCTV Survey vehicles and lorry-mounted jetting units and which has developed a reputation for problem solving in a variety of circumstances including those encountered at Blandford

After careful consideration of the project requirements, ClearView suggested that a high volume Fullers Combination Jetting Unit combined with an Enz Impact Drilling Cutter, supplied by Jetting Systems, could be used to mill a 100 mm diameter hole through the wax. This, in conjunction with a Warthog spinning nozzle, would then break up the remaining wax, which could then be easily removed from the pipelines using flushing. All works would be carried out in conjunction with ClearView’s mainline Pearpoint CCTV Survey unit to enable complete viewing and monitoring of the cutter progress.

An initial CCTV survey of the pipeline was carried out to ascertain the scale of problem, although the full extent remained unknown due to the large quantity of wax present.

The section of pipe in which ClearView had to work was some 80 m long with virtually 100% wax blockage. It was expected that the cleaning work using the cutter arrangement would be completed at a rate of up to 10 m/day. However, in the event, this target advance rate was exceeded by a very significant margin with the whole 80 m length being completely cleaned in just 3 days.

According to Paul Coombes, of ClearView Surveys Ltd: “We did not encounter any problems with the wax removal on this part of the project. This was because prior to arrival we researched all of the suitable products available to complete the work. This was done with the help of our equipment supplier, Jetting Systems. Between us we came up with the most effective method. High Pressure water jetting was tried by other contractors but had limited success.”

Subsequent to the rising clean cleaning effort it was WECs’ responsibility to establish whether there was any diminution of the bar rating of the PVCu rising main after the high pressure cleaning and use of the Enz hammer. This was because it was WEC’s main concern to put the network back to the operational position it had prior to the fire, whilst trying to keep the costs down for the loss adjuster for the candle factory.

To this end Julian Britton commissioned testing of sections of the rising main with samples being sent to Bodycote and Dr David Lowe. Two tests were undertaken, Dichloromethane immersion and Notched C Ring Fracture toughness testing. These indicated that a reduction in the bar rating that the pipe could accommodate and subsequently showed that the original 12 bar pipe had reduced in efficiency by some 50% due to inadvertent damage during removal of the wax. Julian did state that: “This was not a criticism of the contractors as they tried very hard not to damage the pipe in any way.” The rising main section was subsequently replaced using pipebursting techniques.

Commenting on the project for WWCST Julian Britton said: “'Wessex Engineering Construction has been delighted by the fast mobilisation to site of both Barleymans and ClearView and their expertise has been instrumental in returning these sewers to service. The Weirdermann recycling machine from Barleymans was very efficient in removing the wax and ClearView brought innovation to the rehabilitation of the rising main through use of the Enz Technik ‘down the hole hammer’, removing the cadence mechanism to effectively us it as a miniature TBM.”

Commenting on the project from the Barleymans perspective Danny Godfrey, works director said: “All in all the works proved to be an interesting challenge at times, due to the use of such a large machine on such a small diameter sewer. Wessex Water handled the job extremely well and we enjoyed working on their behalf.”

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