Hertfordshire FRS and Delta Fire Smooth Bore Nozzle
In 2012 Hertfordshire Fire and Rescue Service (HFRS) decided to carry out trials to find a replacement for the branch then in use at operational incidents where high flow rates were required. This branch, the Delta DM 600, had been in service for over 12 years and was incorporated into the Service’s Standard Operating Procedure for incidents requiring high flow rates with low branch inlet pressures, as encountered on the upper floors of high rise buildings. Some data was already available from dry riser tests that had been conducted in 2009/10 at high rise premises within Hertfordshire. This comprehensive data detailed flow rates and branch inlet pressures obtainable on the top floor of numerous high rise buildings in Hertfordshire.
While conducting these pressure and flow tests, in particular during exercises conducted at a 13 storey block of flats in St Albans, a potential hazard was discovered in the form of debris being introduced into the hose line from the rising main, causing reduction in flow and in some instances a total blockage at the branch. Further research revealed that debris in risers was not a new problem, as rubbish and in some instances discarded syringes had been found in risers in other parts of the country. With three documented accounts of branch blockages caused by debris from a dry riser, which could potentially have caused total water failure for the branch team in a fire compartment, HFRS issued a Hazard Bulletin to all operational personnel.
Equipped with the data from the dry riser tests as well as information and experience gained by the HFRS from previous branch trials, the project team from HFRS set out to find a replacement for the DM 600. Following several high profile incidents, high rise fire fighting was a very topical subject at the time, with many Fire Services looking into smooth bore branches specifically for high rise incidents. The possible use of smooth bore branches for high rise fire fighting had previously been identified and proposed in a report sanctioned by HFRS in 2007.
Against this background, numerous branches were tested against a set of rigorous criteria devised by the HFRS project team, including weight, ease of handling, ease of operation and in particular, specific flow tests focussing on the four criteria listed below:
- Able to deliver 350 litres per minute (lpm) minimum at 3 bar branch inlet pressure.
- Able to control the flow rate and jet reaction if higher pressures encountered such as 10 bar.
- Able to be used for gas cooling techniques when the branch inlet pressure and droplet size permits.
- Difficult to block with debris.
A range of branches were trialled and were found to satisfy some, or in a few instances, many of the above criteria, but none satisfied all. Consulting with Delta Fire, the HFRS project team were invited to Delta’s manufacturing facility to discuss HFRS requirements. This quickly resulted in a partnership between HFRS and Delta to develop a branch that met all the criteria outlined. Several prototypes were produced and trialled over several months, culminating in the production of the Delta Smooth Bore.
This branch consists of 5 components:
- The body
- The nozzle
- A pair of stacked smooth bore tips 15mm into 19 mm
- A single 24 mm smooth bore tip
In order to achieve the above without major cost implications, Delta was able to adapt existing successful fire fighting branch, the Delta Attack. This branch is already used by some Fire Services specifically for high rise fire fighting and the additions required by HFRS were achievable with the expertise of the Delta technical team.
The new branch has three flow settings of 250 lpm, 375 lpm and 500 lpm at 7 bar branch inlet pressure. It is a simple concept but gives the branch operator great control with regard to flow rate, droplet size and jet reaction. This is very useful when fighting a fire in a high rise building as, depending on the water required, the flow rate can be reduced or increased, with a respective impact on the jet reaction.
For example, a Delta smooth bore branch working on the 18th floor of a high rise building, with the dry riser charged to 10 bar, will have a branch inlet pressure of approximately 3 bar. On the 500 lpm setting the branch will deliver approximately 350 lpm. If this amount of water is not required, then the flow rate can be reduced by selecting the 375 lpm or 250 lpm setting. This will reduce the flow rate significantly, but will have a positive effect in reducing the droplet size and increasing the branch inlet pressure slightly. This would be beneficial if, for example, gas cooling techniques are required.
If the same branch is working on the 1st floor of the same high rise building and the dry riser is charged to 10 bar, the branch inlet pressure encountered will be approximately 8 bar. On the 500 lpm setting the branch will deliver approximately 570 lpm. Selecting the 375 lpm or 250 lpm setting will not only reduce the flow rate to approximately 410 lpm or 280 lpm respectively, but the jet reaction will also be reduced, making the branch easier to manoeuvre.
Due to these selective flow settings, the branch operator has the benefit of selecting, depending on the size of the fire encountered, the amount of water required to extinguish it or make an effective attack.
If, in either scenario, the branch should become blocked by debris, the branch can be shut off by the operator and the end nozzle can be unscrewed, leaving an internal 25 mm smooth bore. At 3 bar branch inlet pressure this will deliver approximately 660 lpm and at 8 bar pressure it will deliver 1090 lpm. The jet reaction with the latter branch inlet pressure will be significant, but this is an emergency situation and gives the branch operator team water as they retreat from the fire situation. The control handle can be closed down to reduce the jet reaction.
Branch in smooth bore mode.
The branch also has a pair of stacked tips 15mm into 19mm to convert the branch from a spray/fog nozzle into a smooth bore. In this smooth bore mode the branch is very difficult to block as the debris has a clear path to pass through. The 15mm and 19mm stacked tips were chosen so that the branch operator has some control over the amount of water (flow) as required. For instance, in the first scenario on the 18th floor, a 3 bar branch inlet pressure with the 19mm smooth bore tip would give approximately 390 lpm and with the 15mm tip this is reduced to 240 lpm. In the second scenario where the fire is on the first floor, with 8 bar branch inlet pressure the 19 mm tip would deliver approximately 660 lpm while the 15mm tip would provide approximately 410 lpm. The choice would rest with the branch operator and depend upon the situation he/she was facing.
As demonstrated by the examples above, the branch is very versatile and capable of delivering close to 400 lpm on any floor of a high rise building in Hertfordshire, in either spray/fog or smooth bore mode In addition; HFRS requested a separate 24 mm tip so that the branch can be used as a monitor. At 8 bar branch inlet pressure in monitor mode, the branch can deliver approximately 1000 lpm.
Assistant Chief Fire Officer Darryl Keen stated “The newly developed branch has been in operation in HFRS for nearly 12 months and the feedback from operational crews has been excellent. Many firefighters find the versatility of the branch is its most useful aspect and, although each HFRS appliance carries three different branches, this branch has become the branch of choice for many firefighters”
ACO Keen also went on to add “that the support provided by Delta in the development of this branch was an excellent example of industry proactively supporting and reacting to their customers needs”.
The Project team
Assistant Chief Officer Darryl Keen HFRS, Bruce Fixter Delta Sales manager, Station Commander Les. Jones HFRS Project lead, Group Commander Paul Hardy HFRS Tech Services manager.
We at Delta are able to adjust the above designed branch ‘The Delta smooth bore’ to your individual requirements.