Laboratory Test: Soot on Surface – Wipe Samples

LCS laboratory offers tests for soot contamination caused by fire. Soot is formed from a fuel-rich flame, when air supply is insufficient. The inner part of any flame contains billions of carbon particles heated to about 600 °C. Elemental carbon emits a yellowish light, familiar to us as the light of a burning candle (see picture on the right). If the temperature suddenly drops or oxygen supply is limited (like in a house fire), carbon particles precipitate on colder surfaces forming a characteristic soot stain.

Soot particles are small (less than 15 microns) and can travel a long distance from original source of the flame. Eventually, soot precipitates on floors, furniture, and walls giving them that characteristic “after-fire” appearance.

Soot is highly adhesive to porous materials, once absorbed by paint, wood or concrete it cannot be extracted using traditional wiping techniques. We highly recommend to collect soot samples ONLY from glass, stainless steel, or glazed ceramic (Examples include: windows, mirrors, decorative vases, stainless steel kitchenware, fridges, decorative plates, elevators, toilet bowl, sinks etc.).  OUR METHOD DOES NOT WORK for samples collected from painted surfaces, wall paint, wallpaper, plywood, floors, or any naturally dusty surfaces.  These all contain soot-like particles that give a positive reading even from the cleanest room.

Samples are collected using alcohol pads (wipes). We can supply the pads or you can purchase them from your local pharmacy. To make the results quantitative, please keep record of the wiped surface. If possible, use 4″ by 4″ or 1′ by 1′ templates.

LCS Laboratory, reports soot in micro grams (μg) per sample with sensitivity of 10 μg/sample.

Please note, that environmental soot is a natural part of the industrial environment. It may be formed by any source of open fire: candles, wood fireplace, oil lamps, oil heaters, and diesel engines. To take into consideration the actual, historical level of soot, you can also collect a few samples from an “unaffected” area of the same property. If those samples result in a readable soot level,  this would be considered a baseline “pre-fire” reading.

As a standard QC procedure, we would recommend submitting a blank sample of wipe gauze.  Once the samples are collected, each sample needs to be placed into an individual Ziploc bag, labeled and shipped to our lab along with a filled request form.

We analyze the samples using an internally developed method. Soot is first extracted from your samples into a water based solution, and separated from dust particles like char, rust, sand, wood and paper dust. The residual solution is further analyzed for soot concentration using UV-VIS spectroscopy.

Common dust can mildly interfere with analysis. Dust from 4 different sources were tested. All dust samples gave a positive soot reading, which can be expressed as μg of soot per 1000 μg of dust (shown in brackets); carpet dust (14μg/1000μg), wood (saw) dust (21μg/1000μg), ash of burnt wood and paper (31μg/1000μg), cement dust from a garage floor (16μg/1000μg).  The interference is generally low and is insignificant for the purpose of the test.

Soot sampling is commonly used as an indicator of initial surface contamination right after a fire. Soot contamination is considered negligible if it was either not detected or the soot concentration doesn’t exceed its historical level.  Repeat soot testing is performed after a professional cleanup and gives an indication of the efficiency of the remediation procedure.

If you’d like to discuss this test or have any questions, please email us.