Environmental effects of large fires

Introduction

Effects on Vegetation

Advantages/Disadvantages of Fire

Large fires can have number effects both positive and negative on the ground in which the fire has occurred. Fire causes damage to the soil by the burning of the litter layer and the organic material that is present in the soil. The purpose of this organic material is that it acts as a layer to protect the soil from erosion. The removal of this layer from the soil causes erosion. Depending on the heat intense of the fire the soil particles might become incapable of dissolving in water thus causing the soil to lose its nutrients. The consequence of this is that rainwater tends to run off the soil rather than to infiltrate through the soil which again leads to the erosion of the soil. This results in very little vegetation growth (Wildland Fire, 2006).

The main advantages that fires can have on the vegetation are that sometimes different species of plants begin to grow on the area that was previously occupied by the fire. When trees decay after been burned, they return even more nutrients to the soil. Another advantage is that the burned ashes that remain after a fire can add nutrients often locked to the soil for trees and other vegetation. Fires can also help to provide a way for controlling insect pests by killing off the older or diseased trees and leaving the younger, healthier trees. When these trees decay, they return even more nutrients to the soil (Wildland Fire, 2006)

Effects on Soil

The effects that fire can has on the soil varieties with every type of fire, as the frequency, duration and intensity of the fire is different each time.The characteristic of the soil also plays an important role that contributes to amount of damage that is done to the soil. The impact fires have on soils include physical, chemical and biological. High soil temperatures can kill soil microbes and plant roots; destroy soil organic matter; and alter soil nutrient and water status. The degree of soil heating during fire depends on a variety of factors, including fuel characteristics, fire intensity and residence time, and properties of the soil and litter layer (Kennard .D & Callaham M.A, 2008).

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Low-intensity fires have a much more positive effect on the soil as they speed up the process of returning nutrients back to the soil where they are again made available to the plants. Burning also increases nitrogen fixation in the soil and thus compensates for nitrogen loss to the atmosphere those results from burning the litter layer. Evidence indicates that low-intensity prescribed fires have little adverse effects on soil properties, and in fact, may even improve soil nutrient availability. On the other hand severe fires alter soil physical properties over a longer time period by consuming soil organic matter, and potentially may increase surface run-off and soil erosion (Kennard .D & Callaham M.A, 2008).

Effects on Air

Prescribed fires may contribute changes in air quality. Smoke consists of small particles of ash, partly consumed fuel, and liquid droplets. Other combustion products include invisible gases such as carbon monoxide, carbon dioxide, hydrocarbons, and small quantities of nitrogen oxides. Oxides of nitrogen are usually produced at temperatures only reached in piled or windrowed slash or in very intense wildfires. In general, prescribed fires produce inconsequential amounts of these gases. Except for organic soils forests fuels contain very little sulphur, so oxides of sulphur are not a problem either. Particulates, however, are of special concern to the prescribed burner because they reduce visibility. The amount of particulate put into the air depends on amount and type of fuel consumed, fuel moisture content, and rate of fire spread as determined by timing and type of firing technique used. Rate of smoke dispersal depends mainly on atmospheric stability and wind speed (The Environment Agency, 2010).

Effects on Human Health and Welfare

Occasional brief exposure of the general public to low concentrations of drift smoke is more a temporary inconvenience than a health problem. High smoke concentrations can, however, be a very serious matter, particularly near homes of people with respiratory illnesses or near health-care facilities.Smoke can have negative short-and long-term health effects. Fire management personnel who are exposed to high smoke concentrations often suffer eye and respiratory system irritation (The Environment Agency, 2010).

Effects on Wildlife

Large fires such as forest fires dramatically affect wildlife. Large animals that habitat these forests such as elk and deer are normally able to move out of the direction of the fire. While the smaller animals normally burrow to escape the fire. The long- term impacts is more important as immediately following a fire, beetles and other types of fungi are attracted to the burned trees. This influx of beetles attracts a large population of woodpeckers, who feast on the beetles. As the woodpeckers dig for beetles, they hollow out holes that will in turn become homes for other bird species such as bluebirds and swallows. And so the cycle of life begins, as animals move back into a burned area almost immediately after the flames have died (Montana, 2001).

Carbon dioxide (CO2)

Large fires release an enormous amount of carbon dioxide been into the earth’s atmosphere. The main consequence of this gas been released into the atmosphere is that carbon dioxide contributes towards global warming i.e. the heating up of the earth’s blanket (The Environment Agency, 2010).

Fire fighting techniques and their environmental effects

Some fire fighting techniques can have negative impacts on the environment. When a large fires break out sometimes it is necessary to create a fire line to prevent the spread of the fire. Fire line construction kills and removes vegetation and it displaces and erodes the soil. This has a negative effect on the environment. Tree feeling also involves tree cutting and vegetation removal. Both small-diameter understory and large-diameter over story trees are felled to construct fire lines and safety zones. These methods do not for the environment but only damage it. Often fire-fighters use different chemicals to try and control a large fire. Some of these include toxic chemical fire retardants. Concentrated doses of retardant in aquatic habitats can immediately kill fish, or lead to algae blooms that kill fish over time (Ingalsbee Timothy, 2004).

Case Study

The Buncefield oil depot explosion

On Sunday 11 December 2005, explosions at the Buncefield Oil Storage Depot, Hemel Hempstead, and Hertfordshire resulted in a large fire on the site the fire was caused by a leak which lead to a massive explosion. The fire burned for several days, destroying most of the site, including 22 tanks containing approximately 60 million litres of fuel (Cabinet Office, 2009).

The Buncefield site is operated by Total and Texaco and is the fifth largest oil storage facility in the UK, storing some 30 million gallons of fuel, including petrol, diesel and aviation fuel supplied by underground pipe work to Heathrow Airport (Hemming, 2006).

More than 180 fire fighters were deployed from 16 fire services, 26 appliances and 20 support vehicles and as much as 300,000 litres of foam concentrate used, resulting in 20 million litres of firewater (Hemming, 2006).

Over 40 people were injured there were no fatalities. Significant damage occurred to both commercial and residential properties in the vicinity and 2,000 people were evacuated on emergency service advice (Cabinet Office, 2009).

During the operation to put out the fire more than large 786,000 litres of foam concentrate was used and some 40 million litres of water were used to try and bring the fire under control (Edie, 2006).

What we do not think about is the 20 million litres of firewater runoff, containing foam and the inevitable pollution from the site. Pollution such as oils and particulates can be separated by centrifuge from the firewater on site. However, the foam used is likely being PFOS-based (Perfluorooctane Sulphonate) or will contain fluorinated material. The only viable way to remove this type of damaging molecule is via carbon tower filtration such as the perfect filtration system – the carbon is then destroyed through incineration. PFOS, as with any other persistent substance, is a List 1 material as described in the Ground Water Regulations 1998. If the firewater contains persistent substances such as PFOS and this firewater finds its way into groundwater, then the environmental implications and contaminationin the groundwater could last for many years – not three weeks like the smoke (Hemming, 2006).

In the aftermath of the incident, environmental monitoring was undertaken by a multi-agency group led by the Environment Agency. Particular attention was given to the impact of contaminated firewater on local water supplies (Edie, 2006).

But fuel and chemically contaminated water used to put out the fire may also seriously pollute the chalk aquifer underlying the Hertfordshire site, which supplies groundwater for the region, the report said. So far, only low-level water contamination has been found. But because water may take years to drain though the ground, the effects of the blast may only be experienced years down the line (Hemming, 2006).