Welcome to issue 35, this time we look at what to do if you suspect Sick Building Syndrome, how to prevent scaling issues in reverse osmosis membranes; and review what the UK's HSE recommends when dealing with the control of Legionella in cooling systems.

In this issue:

• What to do if you suspect Sick Building Syndrome... more >>
• Preventing scale problems in reverse osmosis membranes ... more >>
• Controlling Legionella in cooling systems ... more >>

What to do if you suspect Sick Building Syndrome?

If you start getting complaints from your workforce about the symptoms associated with Sick Building Syndrome, or your supervisors warm of reduced efficiency and staff unease, it is important that you investigate promptly and systematically. The problem may or may not be Sick Building Syndrome. Even if it is, there could be a number of unrelated causes requiring co-ordinated action across a variety of areas. A prompt response can help improve staff morale and make it easier to get at the real causes. However, a hasty and ill-considered response could involve you in a lot of wasted effort and money in making unnecessary changes.

Remember, your investigations will be most cost-effective if checks start with the most likely sources of the problem and you take the simplest actions to remedy faults as they emerge. More costly systems reviews and sophisticated remedial actions should only be considered if the simple approach does not work. You should discuss your approach with your staff or their representatives, for example the safety representative or the health and safety committee.

How do I investigate Sick Building Syndrome?

A reasonable order of priorities for investigation would be:

• Look for the obvious
• Check the symptoms
• Ask the staff what the problems are
• Check procedures and working practices

If these fail

• Seek professional help

Look for the obvious

A sudden increase in complaints after long occupation of a building may well point to an obvious explanation. Before you do anything else just think whether there is something you know of which could be relevant, such as a local epidemic of colds or 'flu', or a breakdown in the air conditioning system. If you can, take prompt remedial action and keep the staff advised of developments.

Check the symptoms

If there is nothing obvious you will need to investigate the symptoms more carefully. Sick Building Syndrome symptoms are common in the community at large and the number of complaints may simply reflect what is normal in your area. On the other hand, they might also reflect the early stages of a more serious problem.

An analysis of staff sickness and absence records could help you to highlight any major problems, for example by pinpointing where in the building the problem might exist, or providing evidence of a viral infection. If there does seem to be a specific medical problem you will need to get a doctor or occupational health nurse to interview the sufferers and advise you on possible causes and remedies.

In the main, however, Sick Building Syndrome symptoms do not lead to time off work. So the best way to check the symptoms will probably be to ask the staff themselves the following questions:

• What are the symptoms?
• How frequently, and at what time of day, do they appear?
• How long have they been going on?
• Do they go away after leaving the building?

A group of experts working with the Royal Society of Health has designed a questionnaire specifically for this purpose. It could enable you to identify whether or not your problem is Sick Building Syndrome and give information on parts of the building, groups of staff or time of day particularly affected.

Ask the staff what the problems are

If your investigation of the symptoms does not point to the cause of your problem, you will need to look more closely at the workplace environment. The easiest way to highlight problems is, again, to ask the staff themselves. They will generally be the first to know about problems with temperature control, lighting, noise levels, stuffiness, fumes and tobacco smoke. You may also learn something about people's attitudes to their work. These can also be important clues in the search for the causes of Sick Building Syndrome.

For more detailed information about the situation, you can combine canvassing staff opinions with your survey of symptoms or with a more wide-ranging attitude survey. The important thing, however, is to encourage staff to make their views and complaints known by assuring them that action will be taken to alleviate problems where it is reasonably practicable to do so.

But remember, complaints may tell you more about the personal preferences of those putting forward the complaints than point to real problems with the working environment. For example, one person's "draught" will be another person's "fresh air". Survey results need to be carefully interpreted if they are to help you get at the real problem.

Check procedures and working practices

If action on specific staff complaints does not alleviate the problem, you will need to carry out a comprehensive review of the building services, maintenance and cleaning procedures. Where appropriate, you should compare these with the specification drawn up when the building was commissioned or when equipment was installed, and remedy discrepancies. In most cases, this work should be within the capabilities of your own specialist building services personnel or contractors.

You may also need to review other relevant areas related to the working environment such as work organisation.

Seek professional help

If, in spite of all your efforts, symptoms persist, you may need to call in expert professional advice.

Building service engineers will be able to assess the performance of the building services, particularly their ability to cope with the demand produced by the occupants and the work activities.

Occupational health doctors or nurses can examine affected workers to identify whether they have been exposed to irritant, allergenic or toxic substances.

Occupational hygienists will be able to assess likely sources of such exposure, and to measure the indoor environment (eg temperature, humidity and rate of air movement). Sampling and monitoring indoor air for pollutants is normally only of value in certain situations, for example if there is a known source of a particular compound or to identify the source of a suspected pollutant. Pollutants in offices are usually present at very low levels and there is little information on what levels are acceptable.

Ergonomists can advise on job and workstation design.

Management specialists will be able to advise on organisational factors affecting morale and job satisfaction.

For further information or specialist advice please call Accepta on +44 (0) 161 877 2334 or email info@accepta.com.

Content extracted from the HSE document “How to deal with sick building syndrome”, and is reproduced in accordance with Accepta’s agreement with and courtesy of the United Kingdom’s Controller of HMSO and the Queen’s Printer for Scotland.

Top ^^

Preventing Scale Problems in Reverse Osmosis Membranes

Reverse osmosis, often abbreviated to “RO” is a separation process that uses pressure to force a solvent through a special membrane that retains the solute on one side and allows the pure solvent to pass to the other side. RO is used extensively in many commercial and industrial applications and forms an important part of many water purification processes.

Commercial reverse osmosis systems have at their heart a complex membrane that is essential to the reverse osmosis process. Most RO membranes are formed from hollow fibre or thin film composite sheets, and allow pure water to pass through the membrane barrier, rejecting unwanted contaminants and dissolved solids. If such a membrane becomes damaged or contaminated it can lead to reduced output efficiency, increased costs and reduced water quality. It is therefore important to keep these RO membranes in a good, clean condition in order to maintain operational efficiency and optimise running costs.

Membrane Scale Problems

As water enters an RO system it passes along the membrane surface. As this process occurs the solids concentration of the water entering the system can often increase, and “sparingly soluble” salts that are already present can begin to exceed their solubility and precipitate out. When such precipitation occurs, particularly onto the membrane surface itself, membrane fouling results and this may lead to reduced output and an increase in product water conductivity. The most undesirable of these precipitated solids being calcium carbonate and calcium sulphate. If a membrane is to function effectively it is essential that the precipitation of these salts is prevented.

De-alkalisation

Traditionally, techniques involving the use of sulphuric acid were used to prevent the precipitation of calcium carbonate and calcium sulphate, a technique known as “de-alkalisation”. However, there were a number of problems associated with this approach that included the hazardous handling of sulphuric acid, increased sulphate content and increased corrosivity of the water on both sides of the membrane. Although calcium sulphate problems were eliminated these factors led to reduced plant recovery rates and efficiency and hence, increased costs.

Effective Scale Inhibitors – What to Look For?

An effective RO membrane scale inhibitor should be:

• Both safe to handle and safe to use.
• Good at reducing scale problems.
• Be membrane compatible.
• Effective across a wide pH range.
• Compatible with other products.
• Cost effective.

Iron Fouling

It is also normal operating practice to keep residual iron levels in the RO feed water as low as possible, normally below a maximum set by the RO membrane manufacturers. Precipitated iron is a membrane foulant and adversely affects the performance of many antiscalants and so should also be avoided.

Membrane Antiscalant

Accepta 2051 has been developed to overcome the hazards associated with the use of acid in RO systems. It offers excellent performance characteristics and is a high performance, general purpose membrane antiscalant for use in sea water, brackish and process waters and can be used in place of acid control programmes and is also an effective iron sequestrant.

Further Information & Specialist Advice

For more information on Accepta’s membrane antiscalant, Accepta 2051 or if you need RO related advice please call our specialist team on +44 (0) 161 877 2334 or email info@accepta.com.

Top ^^

Controlling Legionella in Cooling Systems

Part 10 of the HSE's Approved Code of Practice "Legionnaires' disease: The control of legionella bacteria in water systems"

Guidance - Cooling systems

There is a range of evaporative cooling systems available which vary considerably in size and type. These systems are designed to dissipate heat, using water as a heat exchange medium, from industrial processes and air-conditioning systems. However, such systems can provide an environment for the growth of many micro-organisms, including Legionella, which can be spread widely by aerosol into the area around the cooling tower.

Processes and systems

Cooling towers/evaporative condensers

There are two main types of evaporative cooling towers: (a) mechanical draught; and (b) natural draught. Mechanical draught towers use fans to move the air through the tower. The air can be either forced or induced through the tower. The forced draught tower, with the fan located in the side, pushes the air through the tower and out at the top. Conversely the induced draught tower, with the fan located at the top, pulls air through the tower and out at the top. In natural draught towers the warm return water heats the internal air causing it to rise. Cooler air is drawn in at the tower base and passes through the falling water droplets, causing evaporation.

Heat removal and dissipation is achieved primarily by the evaporation of a portion of the recirculating cooling water. To optimise the cooling process there needs to be a large area of contact between the water and the air stream flowing through the cooling tower. This is achieved either by distributing the water over a system of splash bars or filming the water over a large surface area of packing.

Different types of cooling towers and equipment are used because of the very wide range of cooling process applications. Open recirculating cooling systems are widely used in industry. Natural draught hyperbolic towers are commonly used in the power generation industry. Chemical, petro-chemical and steel industries may also use such towers but, more often, induced draught towers are used. Smaller industrial plants use forced or induced draught cooling towers. The cooling tower used will depend on the nature of the system duty.

Evaporative condensers are sometimes used for air-conditioning or industrial cooling applications. The evaporative condenser combines the function of both the cooling tower and the conventional condenser, as water is sprayed directly over the cooling coils. The volume of water in the evaporative condenser is usually less than in a cooling system. However, cases of legionellosis have been attributed to evaporative condensers and they should therefore be regarded as presenting a similar risk and requiring similar precautions.

Air-conditioning systems

Air-conditioning is a process of treating air to control its temperature, humidity and cleanliness and distributing this air to meet the needs of the conditioned space. Since temperature and relative humidity are interdependent, typically control is established by passing the air over chilled or heated coils and this may include humidification. The air is cleaned by filtration and heat from the refrigeration cycle is removed by the condenser which is often cooled by water from a cooling tower. The cooling water is heated to around 30°C and with the potential for scale formation, corrosion and fouling this may provide an environment for the proliferation of legionella.

Alternative methods of cooling

In some circumstances it may be possible to use alternative methods of cooling. Dry cooling, for example using air blast coolers or air-cooled condensers, will avoid the risks presented by a wet cooling tower or evaporative condenser. The option of dry cooling should therefore be considered, particularly when cooling towers are due to be replaced or when new cooling systems are planned. Large dry cooling systems have some disadvantages as they are generally larger and heavier than cooling towers, so they may be impractical where space and load limitations are limited. They may also be noisier and, while running costs and energy use are comparable for small units, cooling towers are generally cheaper to run for larger systems. These drawbacks will be partially offset by reduced maintenance requirements and savings in the use of water treatment chemicals, cleaning and disinfection costs, regular monitoring and management costs. Adiabatic cooling systems are used increasingly but if used intermittently, they may pose problems associated with water stagnation; this may result in microbiological proliferation. In practice, each case should be considered on its individual merits.

The ACOP says that plant or water systems should be designed and constructed to be safe and without risks to health when used at work. The following section on design and construction offers guidance on how to do this in cooling systems

Cooling systems should be designed and constructed so as to control the release of drift, to aid safe operation, cleaning and disinfection (see BS 4485:Part 3: 1988 and BS 4485:Part 4: 1996).6 In particular, the following points should be considered:

(a) Drift eliminators, usually made of plastic or metal, should be installed in all towers. In spite of the name, the function of a drift eliminator is to ‘reduce’ rather than actually ‘eliminate’ aerosol drift. Although some types are more effective than others, there is no industry standard. However, they should be well fitted and selected on the basis of their ability to reduce the release of small water droplets – there should be no visible drift released from the tower. Wooden slats do not control the small droplets and should be replaced. Operating conditions, especially the discharge air velocity, affect the efficiency of drift eliminators, for example, if the fan is not running. They are not always fitted on natural draught cooling towers because they may be ineffective.

(b) The area above the cooling tower pond should be as well enclosed as possible to reduce the effects of windage. Wind movements around the tower may cause spray to escape through the sides, especially if it is poorly enclosed. This is particularly significant when the tower runs with its fan off. It may also be necessary to screen the tower or its pond to prevent the entry of birds, vermin, leaves or other debris or contaminants and to reduce solar heat gain.

(c) The water distribution system within the cooling tower should be designed to create as little aerosol (ie small water droplets) as possible. The water circuitry should be as simple as is practicable, with the avoidance of deadlegs and ‘difficult to drain’ loops and bends. Easily understood and accurate schematics of the various water circuits should be available, with any deadlegs or dead ends highlighted and redundant pipework removed. The absence of water circulation means that any microbial population can be left undisturbed for long periods, allowing growth and multiplication. Any subsequent disruption of the deadleg/dead end could lead to a rapid colonisation of the water system.

(d) Those parts of the tower which become wet should be accessible for cleaning; packs should be readily removable and easily dismantled. The wetted areas of the tower should, where possible, be shaded from direct sunlight to discourage the growth of algae. The pond should have a sloping bottom with a drain connection at the lowest point which is large enough to carry away water and slurry quickly and easily. A suitably-sized drain-down valve should be located at the lowest point of the system so that it can be conveniently and completely drained, including all pipework and items of equipment. It may be necessary to fit supplementary drain valves to the bottom of individual items of equipment.

(e) The tower should be constructed of materials which can be readily disinfected and which do not support microbial growth. Preserved (see BS5589:1989)7 timber may be used for the manufacture of cooling towers and packs but it needs to be impervious and easy to clean and disinfect.

(f) Make-up water may not necessarily be mains-supplied (or from another treated water supply) – it may come from rivers, lakes, bore holes and other sources. It may therefore need pre-treatment to be of equivalent quality to the mains supply. If it does not come from a treated water supply, then the quality of water entering the make-up system may show considerable variation in both chemical composition and microbial activity. This may contribute to potential risk and a strategy is required to overcome any identified problems. Inclusion of a water meter in the tower supply pipeline both for the measurement of make-up rates and for the proportional dosage of treatment chemicals is recommended.

(g) A full water treatment programme should be integrated into the system design, with provision made for sample, injection, bleed and drain points and for the incorporation of dosing and bleed equipment; ideally this should be automated.

(h) Cooling towers should be positioned as far away as possible from air-conditioning and ventilation inlets, opening windows and occupied areas, taking note of the prevailing wind direction and the wind distribution over neighbouring buildings. This should also be considered when replacing old cooling towers as it may be possible to reposition them to a more suitable location.

For further information or specialist advice please call Accepta on +44 (0) 161 877 2334 or email info@accepta.com.

Extracted with permission from "Approved Code of Practice (ACoP) and Guidance "Legionnaires' disease: The control of Legionella bacteria in water systems" (L8)" © Crown copyright

Top ^^