Observation techniques for evidence gathering
Issuing a smoke abatement notice (SAN) relies entirely on visual evidence of excessive smoke gathered by an authorised officer of a local authority. The issuing of a Penalty Notice for failing to comply with a SAN also relies on visual evidence of excessive smoke. Thus, it is important to be very thorough in the gathering of this visual evidence and in keeping adequate records of the observations. There is no method prescribed by the Protection of the Environment Operations Act 1997 or the regulations in relation to observing excessive smoke from a residential premises. These notes are intended only to provide some guidance and suggestions for observing excessive smoke from residential premises. Councils may wish to adapt these suggestions to meet their own particular requirements.
- Excessive smoke is defined as the emission of a visible plume of smoke from a chimney for a continuous period of not less than 10 minutes, including a period of not less than 30 seconds when the plume extends at least 10 metres from the point at which the smoke is emitted from the chimney (see s 135A of the POEO Act). (Note: s 135A of the Act defines 'chimney' and 'residential premises'. These definitions are provided in Overview of legislative provisions for smoke abatement notices.)
- A SAN may be issued within 7 days of when an authorised officer of an appropriate regulatory authority that is a local authority observes excessive smoke emitting from a chimney on or in residential premises. More information is available under Evidence gathering (see also s 135B of the POEO Act). A SAN may be issued to the person whom the authorised officer believes to be the occupier of the premises and directs the person to ensure excessive smoke is not emitted from the chimney of the premises at any time after 21 days from when the SAN is issued (s 135B(1)). Issuing a SAN is the first step in the formal process to ensure excessive smoke is not emitted from a residence. In most cases, the occupier will have already been alerted to the fact that their heater emits more smoke than it should. This means that the occupier will generally have received a brochure explaining why wood smoke is a problem and how to operate and maintain a heater to minimise smoke.
- A contravention of a SAN occurs when a person to whom the SAN was given fails, without reasonable excuse, to ensure that excessive smoke is not emitted from the chimney of the residential premises in relation to which the SAN was issued. This contravention must occur more than 21 days after the date the SAN was issued, and while the SAN is still in force (see s 135C(1)) (SANs have effect for 6 months, unless earlier revoked: see s 135B of the POEO Act and the section on Evidence gathering in this document.
- The information below contains guidance and suggestions for observing excessive smoke and record keeping in relation to observations, and covers:
- smoke observation techniques for gathering evidence
- suggestions for record keeping
- issues influencing smoke visibility
- estimating the length of smoke plumes
- photographing and videoing smoke plumes.
These notes provide suggestions and guidance for authorised officers of local authorities on making visual observations of excessive smoke relevant to s 135B and s 135C of the POEO Act.
- Visual evidence may be used when issuing a smoke abatement notice (SAN) or establishing that a contravention of a SAN has occurred.
- Formal observations are likely to commence after an authorised officer of a local authority has noticed a smoke plume from a chimney on or in residential premises that seems to extend beyond 10 metres from the chimney.
- The authorised officer should select an appropriate, convenient and safe location for making observations (e.g. standing nearby) and should make sure that they have a clear line of sight to the chimney. The discharge point (top) of the chimney should be visible from the observing position. Nearby buildings, vegetation and the location of the chimney on or in the residential premises might make it difficult to see the smoke discharge point from any public land. In these cases, authorised officers may need to seek permission from the occupier of the residential premises or a neighbouring property to enter that property and observe the smoke. The length of the smoke plume is often easier to judge if the plume direction is roughly at right angles to the direction of observation.
- The time that the observation commences should be noted. Ideally a stopwatch could be used to time the smoke emission (noting the time that the observation commenced and finished). Visible smoke must be emitted from the chimney for 10 minutes or more. During this period it is reasonable to glance at a watch but the authorised officer should try not to look away from the smoke emission for more than a few seconds when glancing at their watch/stopwatch. The authorised officer should not attend to any other business that would distract his/her attention.
- During the observation period (of 10 minutes or more) the visible smoke plume must extend for a distance of 10 metres or more from the discharge point of the chimney for at least a continuous period of 30 seconds. The time (and the length of time) when the visible smoke plume exceeded 10 metres in length from the discharge point should be noted. This observation requires an estimate of the length of the smoke plume.
- Information about the observation that the authorised officer considers relevant should be recorded as soon as practical after making the observations. Some of the information that an authorised officer might record is discussed below under record keeping.
In the case of issuing or observing a contravention of a SAN four aspects of the observation are important: the fact the smoke plume is visible, whether or not the plume is visible for 10 minutes, whether or not the visible plume extends more than 10 metres for at least a 30 second period and whether the smoke plume is emitted from a chimney on or in residential premises. It is suggested that authorised officers make notes as follows:
- As soon as is convenient, preferably immediately after making the observations, prepare a written record of the observations.
- Note that the smoke plume was visible and the source of the plume was a chimney on or in residential premises. Local authority records can be checked to confirm whether a premises is a residential premises. The top of the chimney (discharge point) should be visible from the observing position.
- Note the time and date when observations commenced and the time when observations ended (minimum 10 minutes) (if a stopwatch is used record the length of time shown on the stopwatch and the time that the observation commenced and/or finished) and the fact that visible smoke was emitted throughout this period. The date is important because a SAN must be issued within 7 days of the observation of excessive smoke being made. An offence of failing to comply with a SAN can only be committed after 21 days from the date the SAN was issued and while the SAN remains in force.
- Note the time (and the length of time) when the visible smoke plume exceeded 10 metres in length from the discharge point. This must occur for a continuous period of at least 30 seconds.
- Note the length of the smoke plume and how the length of the smoke plume was estimated, including any objects or reference points used to estimate the length of the plume (see point 9 below). For more information on estimating distances see Estimating smoke plume length.
- Record the address of the premises emitting the smoke plume.
- Record any evidence used to establish the occupier of the residential premises, e.g. conversations with persons at the residential premises or records held by the local authority.
In addition to the above records, it is suggested that the following information should be noted:
- Record the general observing conditions as appropriate (such as wind strength and direction, cloud cover, sunlight, whether the street lights were turned on, weather (e.g. raining), location of any other objects emitting smoke in proximity to the chimney of the residential premises).
- Note the position of the chimney on the residential premises.
- Prepare a sketch map of the observing position, residential premises, chimney, nearby landmarks if used to judge plume length, and smoke plume (including the direction of the plume). If practical, the map could also note the location of sun, colour of the smoke plume, and location of any other objects emitting smoke in proximity to the chimney in question.
Observing smoke plumes
Visible wood smoke is made up of tiny droplets of organic oils and tars that escape as unburnt gas when wood is heated in a fire. If the combustion conditions are poor, as much as 10% of the weight of the wood escapes as unburnt gas and forms a dense, pungent plume of smoke as the gas condenses into droplets or particles of wood smoke. When wood is burnt well, less than 0.1% of the weight of wood is emitted as smoke particles/droplets. Individually these droplets are too small to be seen without the aid of a strong microscope, but when present in high concentrations they scatter light causing the smoke plume to become clearly visible as a white or pale blue plume. When wood is burnt well no smoke plume is visible.
Because the light is scattered by a plume of wood smoke, rather than reflected or absorbed, it is most clearly visible when light is passing through the plume (see sketch below). This property of smoke plumes means that the smoke is more visible when the sun is relatively low in the sky (early morning and late afternoon), but very thick smoke is visible at any time during the day. Street lighting can make smoke plumes visible at night in some circumstances. Torches, spotlights and flash cameras have not proved very useful in observing smoke plumes after dark.
Other factors, such as the position of a house relative to the street (line of sight), wind direction, the times of day that a heater is used and the availability of authorised officers, may mean that less than ideal observing conditions are often encountered. In these circumstances, it is best to make initial smoke observations from several convenient locations to determine the most appropriate location for the formal observation.
A smoke plume will often be seen twisting in complex shapes as it moves in turbulent air flows around a structure. The estimated length of the plume should be a straight line distance from the chimney top to the end of the plume.
Estimating smoke plume length
Authorised officers may issue a SAN if it appears to the authorised officer that excessive smoke is being (or has within the past 7 days been) emitted from a chimney on or in a residential premises. Excessive smoke is the emission of a visible plume of smoke for not less than 10 minutes including a period of not less than 30 seconds when the plume extends at least 10 metres from the discharge point. Authorised officers may estimate whether the plume extends more than 10 metres, however officers should be able to justify this estimation. It is important to be able to justify the estimated length of the smoke plume to establish that the smoke plume reached or exceeded 10 metres. Essentially, an estimate of distance will rely on common sense. The use of various geographical features is one useful way of establishing the distance. For example:
- The distance along the road frontage of the property could be used to estimate the length of the smoke plume. This could be confirmed from plans or by measuring it.
- Nearby trees, power poles, or neighbouring houses along the line of the smoke plume are useful geographic indicators that can provide a material reference point to establish the length of the plume.
- The height of the house or other nearby objects with known dimensions can be used as a mental yardstick to judge plume lengths.
- When using features such as these, record the objects used to judge distance in your notes.
Photographing or videoing smoke plumes
Photographs of smoke plumes usually do not capture as clear an image of the plume as is apparent through visual observation, in other words the photograph tends to understate the thickness and length of the plume. However, photographs can provide useful visual evidence of the smoke and should be taken if practical in the circumstances discussed below.
- One of the reasons smoke plumes are visible is the constant movement of the smoke. This rapid changing in how clearly parts of the background can be seen catches our attention. For this reason short video clips of smoke plumes tend to show the plume more clearly than a still photograph. Many digital cameras have a capacity to record short video clips, or longer records can be obtained with video cameras.
- The smoke plume will show up most clearly under good viewing conditions in the early morning or late afternoon.
- The smoke will also be more visible when there is a darker background of hills, trees or buildings.
- Photographs of smoke plumes against clouds usually show poor resolution of the plume. In such cases a short video clip is often the only practical means of obtaining a visual record of the smoke.
- It is useful to gain some experience in taking photographs of smoke plumes before using this method to support the evidence presented in a prosecution regarding a contravention of a SAN.