Schematic drawings – Are they required? How detailed should they be?

There is huge inconsistency amongst companies and risk assessors about whether schematic drawings are required for a risk assessment, who produces them and what level of detail they need to be. Sadly, as with a number of technical aspects of this industry there is conflicting information in the guidance we follow. This leads to companies taking different views and leaves customers at the mercy of their interpretation.

Here is some information taken from the Technical Guidance HSG274 Part 2 and my thoughts:

Page 5, paragraph 13: “the risk assessment should consider and evaluate… a description of the water system, including an up-to-date schematic diagram”

MH comment - This implies a schematic should be available and is a necessary part of the risk assessment.

Page 5, Info Box: Schematic Diagram: “A schematic diagram is a simplified but accurate illustration of the layout of the water system, including part temporarily out of use”. “These are not formal technical drawings but show what the systems comprise of, illustrating plant equipment, including services and control valves, any components potentially relevant to the legionella risk, including outlets, strainers and filters or parts that are out of use.”

MH comment – This is meant to be a ‘simplified' schematic and not ‘formal technical drawings’, however, to include all the mechanical components suggested above you are producing a drawing akin to a formal technical drawing (as-fitted drawings), so this is contradictory! The difference between creating a simplified schematic and formal technical drawings is huge from a time perspective, and therefore has a cost implication. There is a big difference in access requirements too.

Page 55, Appendix 2.2 Legionella written control scheme: “…information to include in a legionella written control scheme… up-to-date schematic plan showing the layout of the system(s)…”

MH comment - This implies a schematic should be part of a customer’s written scheme.

Page 27, paragraph 2.64 Subordinate and tertiary HWS loops,

Page 31 Table 2.1 Checklist for hot and cold water systems and

Appendix 2.5 Example of sentinel points in a complex hot water system (HWS).

MH comment – For complex recirculating hot water systems HSG274 Part 2 recommends taking temperatures from the return leg of subordinate and tertiary loops. In order to identify these locations you need a very detailed schematic drawing. This implies that formal technical drawings (as-fitted drawings) are required for complex recirculating hot water systems.

For healthcare customers following HTM 04-01, the guidance is more clear cut.

HTM 04-01 Part B, paragraph 5.1 Operational Management:

"Managers should ensure that an operational plan is in place for each site under their control. This document should comprise:

a. up-to-date as-fitted drawings, schematic diagrams and descriptions of all the supply, storage and distribution systems within those premises;"

MH comment – Healthcare premises following HTM 04-01 will require up-to-date as-fitted schematic drawings if they wish to fully comply.

Watermark Compliance view:

We believe that a ‘simplified’ schematic should be provided with every legionella risk assessment. This helps to demonstrate that all areas of the system have been accessed. By identifying all assets it helps the client set up a monitoring regime, for example, knowing the location of all thermostatic mixing valves (TMVs). When we encounter complex water systems such as those in hospitals or factories we supply an Asset Register instead, which shows this information in a tabular format. Be aware that some companies may sell risk assessments with no schematic drawings and then charge for this additionally at a later date.

For complex water systems with hot water subordinate and tertiary loops, we recommend customers have formal technical drawings (as-fitted drawings) produced. Be aware that most water hygiene companies do not have the capability to produce drawings of this detail and complexity. These are typically provided by engineering companies and should not be confused with simplified schematics.