50 mg/L and the whole chlorination certification myth…
The stated new main chlorination specification required for free chlorine level is generally documented as 50 mg/L (ppm) for 1 hour in the PD855468:2015 (the TGN 2 does quote 20 mg/L but this has a 16 contact time).
Yes you can achieve the elusive 50.0 mg/L as shown here but it is very difficult to get exactly 50 mg/L when using digital equipment as there are many variables such as background demand, temperature and pH of the parent main water so even with highly sophisticated dosing equipment such as ours there are acceptable variances.
As 50 mg/L is stated many chlorination companies consistently write 50 mg/L at both the start and at the end of chlorination on their certification and this should ring alarm bells.
If something were to be challenged this very point would be scrutinised and questions asked.
Generally it comes down to a number of factors including the following:
- Poor test equipment or worse still no test equipment. Many companies use inaccurate test strips that at best give a very wide range between visual interpretation measurements and at worst show very little other than the presence of a reasonable amount of chlorine. Digital equipment is readily available so ask why it is not being used. Cost, competence or both? However, you as the client end up with the risk of failed connections and increased cost.
- Inexperience or poor training. You often can’t blame the engineers as this training and expertise should come from the top tiers of the company but if this is missing or the emphasis is purely on financial gain then this will not filter down to the chlorination engineers on site. If the engineers aren’t trained in something as fundamental as using the correct test equipment think how well trained they are in other areas?
- Sub-contracting. Not only will you most likely pay more if you end up with a subcontractor but often there is a reduction in accountability and this can often manifest on site as poor quality work resulting in failed connections.
- Colour blindness. Some engineers are colour blind and when relying on a visual colorimetric scale they are unable to determine the actual chlorine level in the mains. Not their fault but again a risk to your connection.
Think about this… We all have a computer in our pocket (mobile phones) so why are we still happy to accept the most basic technology or a small, one use, plastic strip to test for chlorine? Insist on digital measurements and insist on photographs of said as proof of effective disinfection.
This will give accurate mains chlorination certification that will stand up to scrutiny by the Water Authorities and will give them confidence in granting your new main connection, giving you water to your investment and easing the stress.