Preventing or controlling the risk from exposure to legionella bacteria

Question 1

Where the assessment shows that there is a reasonably foreseeable risk
of exposure to legionella bacteria, the use of water systems, parts of water
systems or systems of work that lead to exposure must be avoided so far as
is reasonably practicable. Where this is not reasonably practicable,

Answer 1

there
should be a written scheme for controlling the risk from exposure that should
be properly implemented and managed. The written scheme should specify
measures to take to ensure that it remains effective.

Question 2

The risk from exposure should normally be controlled by measures
which do not allow the growth of legionella bacteria in the system and which
reduce exposure to water droplets and aerosols. Precautions should, where
appropriate, include the following:

Answer 2

(a) avoiding water temperatures between 20 °C and 45 °C and conditions
that favour the growth of legionella bacteria and other microorganisms;
(b) avoiding water stagnation which may encourage the growth of biofilm;
(c) avoiding the use of materials that harbour bacteria and other
microorganisms, or provide nutrients for microbial growth. The Water
Fittings and Materials Directory 10 references fittings, materials, and
appliances approved for their compliance with the UK legal requirements
for plumbing fittings and water using appliances;
(d) controlling the release of water spray;
(e) maintaining the cleanliness of the system and water in it;
(f) using water treatment techniques;
(g) taking action to ensure the correct and safe operation and maintenance
of the water system.

Question 3

The written scheme should include, where appropriate, and with
reference to the risk assessment:

Answer 3

(a) an up-to-date plan showing the layout of the plant or water system,
including parts temporarily out of use (a schematic diagram is sufficient);
(b) a description of the correct and safe operation of the system;
(c) the precautions to take;
(d) checks to carry out to ensure the written scheme is effective and the
frequency of such checks;
(e) the remedial action to take if the written scheme is shown to be not
effective.

Question 4

The written scheme should give details on how to use and carry out the
various control measures and water treatment regimes, including:

Answer 4

(a) the physical treatment programme – eg using temperature control for hot and
cold water systems;
(b) the chemical treatment programme, including a description of the
manufacturer’s data on effectiveness, the concentrations and contact time
required;
(c) health and safety information for storage, handling, use and disposal of
chemicals;
(d) system control parameters (together with allowable tolerances); physical,
chemical and biological parameters, together with measurement methods and
sampling locations, test frequencies and procedures for maintaining
consistency;
(e) remedial measures to take in case the control limits are exceeded, including
lines of communication;
(f) cleaning and disinfection procedures;
(g) emergency procedures.

Question 5

The written scheme should also describe the correct operation of the water
system plant, including:

Answer 5

(a) commissioning and recommissioning procedures;
(b) shutdown procedures;
(c) checks of warning systems and diagnostic systems in case of system
malfunctions;
(d) maintenance requirements and frequencies;
(e) operating cycles – including when the system plant is in use or idle.

Question 6

For precautions to remain effective, the condition and performance of
the system will need to be monitored. The appointed responsible person
should oversee and manage this. Or, where appropriate, an external
contractor or an independent third party can do it. Management should
involve:

Answer 6

(a) checking the performance and operation of the system and its
component parts;
(b) inspecting the accessible parts of the system for damage and signs of
contamination;
(c) monitoring to ensure that the treatment regime continues to control to
the required standard.