TECHNICAL 41
For this revised article , I thought a brief listing of areas of concern , activities an installation types would be in order , also a brief list of the more common types of backflow prevention devices used . I then want to give some examples of documented backflow incidents to sober us all up .
Please remember though , that this is just an article , not a substitute for knowing the standards . Remember also to consult your local authority for any additional requirements regarding backflow prevention
The following are some examples of where and when backflow prevention should be present : 1 . Any fire installation or combined installation 2 . Medical treatment of people or animals . 3 . Medical , pharmaceutical , or chemical research and manufacturing . 4 . Agriculture , including dairies and nurseries . 5 . Laundering and dry-cleaning . 6 . Photographic processing . 7 . Metal plating ; or 8 . Treatment of hides and skins . 9 . Any installation with hoses attached to fittings 10 . Boat yards 11 . Clinics 12 . Fields or parks 13 . Irrigation systems
Here are some examples of common backflow prevention devices . Note that not all devices are suitable for any type of hazard . The risk level of a particular hazard should be determined as either low , medium , or high , and the appropriate backflow prevention device ( s ) should be employed . 1 . Double check valve assemblies 2 . Various types of vacuum breakers installed withing anti-syphon loops 3 . Break tanks 4 . Air gaps 5 . Reduced Pressure Zone backflow preventers ( RPZ )
There are thousands of examples where cross-contamination of potable water took place , and just to remind ourselves why we need backflow prevention , here are a few examples . 1 . June 1983 , Calgary , Alberta , Canada- Veterinary clinic contaminates residential drinking water . E-Coli .
2 . July 1993 , Oregon- Irrigation system pumping from a stagnant pond . Pump breaks is removed for repairs . Occupant wants to irrigate grass , connects hose to irrigation system , backflow occurs . Neighborhood affected
3 . January 1981 , Norfolk Virginia- A shipyard ’ s high pressure fire protection ( pumped sea water ) system was primed using potable water and left open . Pumps overwhelmed potable pressure and seawater flowed into municipal lines . All drinks and food prep at nearby restaurant contaminated . Guests reported all drinks were ‘ salty ’.
4 . January 1990 Brighton , Colorado- Glycol from a school ’ s space heating system backflowed into the water supply due to a maintenance valve being left open . No backflow preventer in place . Several children affected .
5 . October 1991 Southgate , Michigan- Domestic irrigation system supplied by potable water , failed backflow preventer failure ( Atmospheric vacuum breaker ). When a main water line burst , water was sucked into municipal supply . Residents reported ‘ worms ’ in the tap water , later identified as Nematodes .
6 . July 1989 , Cincinnati Ohio- An anti-fungal chemical used in an office building ’ s air-conditioning system backflowed due to no backflow preventer . 12 resultant illnesses .
7 . June 1991 , Casa Arkansas- Backflow of antibiotic solutions used in the poultry industry contaminated nearby homes close to a poultry farm . Existing backflow prevention included two single check valves plumbed in series .
8 . June 1987 , Ontario Canada- 29 workers at an electroplating plant took ill after drinking from a drinking fountain . 11 hospitalized . Cause was a submerged potable water inlet to a rinse tank , with no air gap , and no other backflow prevention .
7.4.3.3 Unless other approved measures are taken to prevent the backflow of water from terminal water fittings that discharge water into a sink , wash-hand basin , bath , or other similar appliance , a . such terminal water fittings shall be so installed that the vertical distance between the point of discharge of the fitting and the spill-over level of the receiving appliance is at least equal to the distance given in table 13 for the size of the fitting concerned . b . a double check valve shall be incorporated as close as is practicable to the point of discharge ; or c . a combined check valve and vacuum breaker shall be so installed that the vacuum breaker is at least 300mm above the spill-over level of the receiving appliance .
Look at section 7.4.3.3 above and think about Nikki spouts in baths . It clearly says here that for fittings that discharge into for example a bath , there must be a gap between the outlet and the spill-over level of the appliance ( not the overflow outlet level — the spill-over level means the rim of the bath ) with a certain vertical distance separating them .
A Nikki spout does not have this gap , so we need to install either ‘ b ’ or ‘ c ’ as above . How many of us do this ? As a side note , in Annexure D of SANS 10252-1 ( D . 1.6.1 ), it says that if the terminal water fitting already has a backflow prevention device incorporated within the fitting that is suitable for the hazard generated , we need not install additional backflow prevention . Given that a single check valve is not a suitable backflow prevention device , how many of us have installed Nikki spouts that comply ?
In essence , our role here is quite simple : we need to determine the hazard level and from that , we need to decide on the type of backflow preventer we need to install , if any . Note that a break tank with an air gap is also a suitable means of backflow prevention , but not easily employed . Note also that if there is no break tank , the two most
January 2022 Volume 27 I Number 11 www . plumbingafrica . co . za