This is the moment the haunting sound of an air raid siren filled the air in and around Oldbury near Birmingham at noon on Friday 7 October.

The warning alert was due to an annual siren test by Solvay Solutions UK Limited in the West Midlands.

The company produces many different types of chemicals and sounds the alarm during incidents for 5 minutes if chemicals are  released into the air.

The siren was tested for 60 seconds before an all clear was given at 12:01pm.

The annual event was pre-warned by both the council and police to prevent anyone from panicking.

The siren sound travels for about a kilometre in distance depending on weather and wind direction.

Sandwell Council posted on Facebook “Solvay Oldbury will be testing their alarm today (Friday 7 October) at midday.

“The alarm is a very loud siren that will sound for about a minute.

“It will be heard from at least a kilometre away.

“No need to panic - it's just a test. Please share and make others aware.”

Solvay handles materials that include toxic, very toxic, highly flammable, dangerous to the environment and corrosive ingredients.

The plant is located in the shadow of the elevated section of the M5, close to Junction 2 and is on the outskirts of Birmingham.

Advice given to the public by Solvay on what to do if the alarm is sounded for real:

“In the unlikely event of a major emergency involving the release of a toxic substance, the off-site siren would be sounded for five minutes and the police would issue information and advice via the local radio and television channels and by any other means deemed appropriate.

“It is important that you cooperate fully with any instructions from the emergency services.

“After any gas cloud has passed, the police, through local radio stations, would broadcast advice on the action to be taken.

“Anyone affected by toxic gas fumes and experiencing breathing difficulties, should be kept at rest with head and chest raised, and kept warm until medical attention is available.

“Advice can be sought from NHS Direct, telephone 111.

“These radio stations would be used by the police to broadcast advice: Radio WM – 95.6 FM BRMB – 96.4 FM”

In 2016, the company was fined 440,000 pounds after a dangerous gas cloud wafter across Oldbury in 2009.

The M5 was shut down, a nearby ASDA supermarket closed and thousands of people were told to stay indoors during the incident on January 2nd 2009.

A dangerous gas of phosphorus and phosphine was unknowingly released and workers and residents who came into contact with the gas had breathing problems and streaming eyes as well as other ailments.

During the incident the police set up road closures, part of the M5 was closed by the Highways Agency, and an estimated 4,500 people were asked to stay indoors for two to three hours.

The released gas was phosphorus and phosphine which, upon contact with air, spontaneously ignited to produce phosphorous pentoxide.

This reacted with the moisture in the air to produce a mist of phosphoric acid which drifted to a densely populated area.

The HSE investigation found a welded steel bar (‘rodder’) failed at the weld and broke in two.

One piece fell back and the other piece pulled clear, leaving an opening through which the dangerous substance escaped.  

The incident was reported to the European Commission.  

Solvay Solutions UK Limited, formerly Rhodia UK Limited, was fined a total of £333,000 and ordered to pay costs of £110,000 after pleading guilty to an offence under Sections 2(1) and 3(1) of the Health and Safety at Work etc Act 1974.