Environment Agency experts say sulphur dioxide levels were elevated by last Thursday’s (February 16) flare-off at the Stanlow oil refinery but remained within allowable limits.
The giant flame from the top of the stack sparked alarm across the region as it turned the night sky orange but there was also concern at the thick black smoke released into the atmosphere.
Essar said the flare was a safety mechanism that allowed excess gas to be burnt off but accepted the flaring was ‘heavier’ than normal.
The Environment Agency monitors the plant to ensure the company complies with its environmental permit.
In 2014, a investigation was launched after the monitoring station at Thornton Le Moors revealed the sulphur dioxide target was exceeded dozens of times during a 12 month period.
Sulphur dioxide is a major air pollutant with the potential to have a significant impact on people’s health, particularly those with heart or lung problems such as asthma.
An Environment Agency spokesperson said on Friday, February 17: “We can confirm we received a call from the public following the flaring at Stanlow Refinery yesterday (Thursday, February 16). Although we had not been told about the flaring, such activity is permitted.
“Our environment officers meet with the site on a regular basis to discuss a range of matters relating to the environmental permit – the frequency and nature of flaring is one of the matters covered. Flaring events are a contributor to emissions from the site and are reviewed periodically as part of our routine compliance work.
“Typical products of combustion are oxides of carbon (CO2/CO), oxides of nitrogen (NOx), sulphur dioxide (SO2) and particulates. Hydrocarbons (derivatives of crude oil) are what’s being burnt off – the quantities emitted are determined by the amount of fuel that has gone to the flare.
“Much of this is dispersed into the atmosphere but there are a number of ground level monitoring stations surrounding Stanlow that measure and report air quality.
“The impact on the environment has been measured by the monitoring station in Elton . Although elevated levels of SO2 were recorded, these met the air quality standard. We would like to reassure the local community that the Environment Agency will continue to regulate the site and review its compliance with their permit.”
Essar spokesman Ian Cotton said of the incident: "Plant maintenance was carried out on Thursday afternoon and this resulted in the activation of a safety control system. On restart of the unit involved, this led to a short period of heavier flaring of LPG (liquefied petroleum gas) than had been planned.
"Flares (which allow the controlled burning of gases) are important safety devices used throughout the refining industry to ensure gases from process plants can be safely handled when required.
"If we plan to have heavy flaring, we notify local community representatives in advance. On this occasion the maintenance work was not expected to lead to heavy flaring, so this was not possible. We do everything we can to minimise flaring at Stanlow.
"Like all other UK refineries, Stanlow operates under an environmental permit and works closely with the government’s regulator, the Environment Agency, to continually reduce emissions.
"Since acquiring the refinery in 2011, Essar has reduced overall sulphur dioxide emissions by 48%. We are working with Cheshire West and Chester Council and the Environment Agency to agree a plan to address the 15-minute SO2 emissions exceedances previously monitored in Thornton-le-Moors.
"Stanlow plays a strategic role in the nation’s economy, supplying 16% of all UK road transport fuels. It is also a major regional employer with over 900 staff, an additional 500 on site contractors and a further 5,000 people employed indirectly through the extended value chain."
In 2015, Essar Oil (UK) Limited was fined £497,284 and ordered to pay costs of £40,000 in relation to two separate pollution incidents at Stanlow which occurred in 2012 after pleading guilty to three breaches of their environmental permit following a prosecution brought by the Environment Agency.
On July 31, 2012, the roof of an oil storage tank failed under pressure at Stanlow Oil Refinery. This caused a plume of steam and oil to be released into the atmosphere and fine droplets of oil were reported over a large area affecting gravestones at Overpool Cemetery in Ellesmere Port .
In a separate incident on August 19, 2012, approximately five tonnes of oil entered the Manchester Ship Canal following failures in the operation of Essar’s effluent management system. As a result of the incident, the Manchester Ship Canal was closed for two days to all shipping traffic whilst an extensive clean-up operation was carried out.