Why do Fire and Flood Damaged Buildings often suffer from bad odours?
Of the two types of disaster, flooding produces the worst odour problems. Even though the damage to the fabric of the building appears to be less than with a fire the penetration of foul smelling river water is very deep and it takes a long time to remove. In addition to the bad odour from drying mud and silt there is the wet fabric of the building that provides an ideal breeding ground for mould to develop, generating further smell.

In fire situations vast quantities of water are used and the effect is similar to that produced by a flood. Although the problems of mud and silt are unlikely to be present, smoke damage in other rooms can be equally troubling.

What is the best way of eliminating the bad odours?
Fresh air will do much to reduce the odours and help to dry the building however the process is slow and in winter, when most floods occur, may be difficult to achieve. Dehumidifiers can get rid of the worst of the water problems but this still leaves the odour to be tackled. Artificial chemical fragrances can be used to mask the smell but these generally only makes matters worse. Ozone has been found to be highly successful in eliminating unwanted odour in rooms affected by fire or flood and provided the amount used is accurately controlled it is the ideal solution. Not only will it eliminate odour but it will also help reduce the moulds and bacteria that may exacerbate the odour problem. The ozone is usually dispensed from a portable unit where it is used to flood a room with ozone while it is unoccupied. The ozone generator can be left running as long as necessary to bring the odour under control.

What is ozone?
Ozone is a naturally occurring substance that is sometimes called "activated oxygen". It contains three atoms of oxygen (O₃) instead of the usual two found in normal oxygen (O₂) that is essential for life. High in the atmosphere the ozone layer is created by the action of the solar radiation on the oxygen atoms. At ground level the unmistakeable fresh smell in the air following a thunderstorm is ozone created by the effect of the lightning discharge on the oxygen atoms. Ozone is also created naturally as a result of photochemical reactions due to the pollutants such as NOx and SOx that are found in the atmospheres of cities and industrial areas. Ozone can also be created artificially by generating a high voltage electrical corona across a dielectric to form what is known as a "silent discharge".

Ozone is the second most powerful oxidant known and the naturally occurring level not only protects all life from the harmful effects of solar ultraviolet radiation but also is very effective at destroying bacteria, viruses and odours. Artificially generated ozone is just as effective as naturally occurring ozone provided that the amount is carefully controlled and this requirement for control is a key consideration when selecting an ozone generator.

How does ozone work?
The ozone gas molecule O₃  is unstable allowing it to readily decay into O₂ thereby releasing a single oxygen atom that is highly reactive. When the ozone comes into contact with an odour or a Volatile Organic Compound (VOC) an oxygen atom splits off from the ozone molecule and reacts with the odour or VOC, oxidising it into harmless and non odorous substances that are predominantly CO₂ and H₂O. The ozone will also react with certain surfaces. When it comes into contact with a bacteria or a virus, the oxygen reacts with the cell membrane. Initially the ozone attacks the glycoproteins, glycolipids and certain amino acids such as tryptophan in the bacterial membrane. It also acts upon the sulfhydral groups and some enzymes resulting in the disruption of normal cellular activity. Bacterial death is rapid and is often attributed to changes in the cell permeability followed by cell lysis.

As each of these reactions occur the amount of ozone present continuously reduces until all the ozone has decayed back to the original normal bi-atomic, oxygen making it a safe and environmentally friendly with no harmful residues. As the ozone molecule is unstable, even if none of these reactions occur the ozone (O₃) rapidly reverts back to oxygen (O₂). As a result of this natural decay back to oxygen the use of an ozone generator in a room does not lead to a continuous build up of ozone. The level of ozone will stabilise at a predetermined level that is a function of the room size, air changes, temperature, odour/VOC/bacteria content and the reactivity of any surfaces. Because these parameters are all highly variable the need for the ability to control any generator used is essential.

What is the right level of ozone?
The occupational exposure levels for ozone vary across the world. In the UK there is no limit on exposure below 0.2 parts per million (ppm). In many European countries there is an eight hour time weighted average exposure limit of 0.1ppm, while in the U.S.A the comparable level is 0.08ppm. The World Health Organisation has an average Air Quality Guideline of 0.05 - 0.06ppm measured over an eight hour period.

Ozone has been shown by extensive laboratory trials to be effective at reducing odour and bacteria when used at levels no higher than 0.05ppm. These levels are considered safe to breathe 24 hours per day. Ozone Industries has found that by accurately controlling the amount of ozone generated it can be used very safely and effectively to destroy unpleasant odours and control bacteria.
In fire and flood situations it usual to flood the room with as much ozone as possible to reduce the odour level quickly. During such treatments people should be excluded from the room.

How is ozone produced?
The silent corona discharge method that mimics the action of the lightning is the most usual method of ozone production for odour control in a room. The corona discharge electrodes are simple and inexpensive to clean or replace and they consume very little electrical energy. The output from the machines can be easily controlled to suit the size of room and the level of odour.

How can you tell the level of ozone?
The level of ozone is dependent upon the size of the room, the output of the generator, the number of reaction surfaces, the number of air changes and the contaminant load. At high concentrations, ozone has a sharp smell similar to bleach that tingles the nose. This tells you immediately that the level is too high and above the occupational exposure limit. At lower levels it has a slightly metallic odour. At this level you are above the naturally occurring levels but likely to be below the occupational exposure limit. Ozone at 0.05ppm and below has a fresh open air smell.

Ozone Industries supply a sizing chart with each ozone generator to enable the user to install and set up the machine correctly for optimum safety. The sizing chart provides easily understood instructions relating to different room sizes as an initial set up. Once the generator is put into service, small adjustments can be made to the output setting in order to achieve the optimum performance as the actual requirements for each room are slightly different.

Further control can be achieved by using a programmable timer built into the unit in combination with the output level setting control. This enables the generator to be automatically turned down or turned off at the most appropriate times of the day or week to suit the use of the room. The incorporation of such controls substantially increases the flexibility of the generator making its range of application almost limitless.
In a badly affected room a portable unit can be used with a count down time control enabling the room to be flooded with ozone while it is unoccupied ensuring that the process is conducted quickly while staff attend to other matters.

Disposable paper test strips are available that change colour depending on the ozone level to aid the user in validating or monitoring a particular set up and these can be very helpful especially in rooms with unusual shapes where poor air circulation can occur.

Maintenance of the equipment?
Although the ozone generator is long lasting and trouble free it does require some attention from time to time to remove accumulated dust and dirt to ensure that it is operating at peak performance. The generator should be cleaned every 3-4 months depending on the environment and level of usage, primarily to remove any dust and dirt that has accumulated. This operation is normally very simple and should take no more than 5 minutes.

The ceramic electrode should be replaced annually.

Fire and Flood Remediation Q & As

© Ozone Industries Limited 2008