Dr Phathutshedzo Khangale is a senior lecturer, department of chemical engineering technology, University of Johannesburg.
He recently published an opinion article that first appeared in The Citizen on 25 July 2023.
A week after Johannesburg experienced an explosion which led to road infrastructure damage in parts of the city centre, officials are still scrambling for answers.
Officials suspect the explosion could have been as a result of a gas leak.
In this case, it is important to understand which gases are transported underground within the vicinity of the affected area.
Gas explosions explained
It is also important to understand the danger which is posed by these gases. Also, it is of interest to understand how a gas explosion could occur.
The area affected by the explosion is a residential and business area and for that reason, one would expect the gases transported underground in that area should be for domestic use.
Gases for domestic use
It is worth noting that there are various gases which are used for domestic purposes, such as natural gas, methane and liquefied petroleum gas (LPG).
All these gases are flammable, meaning they can cause a fire in the event they are exposed to oxygen, which is readily available in the air.
Also, they are normally transported at low pressure, and this leaves a question whether they are capable of causing an explosion similar to what was witnessed in the Jo’burg CBD.
It is my contention that it is less likely the explosion – which occurred in Lilian Ngoyi Street, formally known as Bree Street – could have been caused by any of the gas that could be carried in the pipes which are located underground in the area.
How gas explosion happens
First, for a gas to ignite, its concentration in the air plays a critical role. If a gas is at a concentration below 5%, one does not expect an explosion to occur as a result of a gas leak.
This is because the leak will be so insignificant, and the leaked gas could be diluted in the air rapidly. For this reason, one would eliminate the above as a possible case of explosion in the incident.
Secondly, if a gas is at a concentration of between five and 15%, the explosion will not lead to a fire.
However, one would expect physical damage on the leaking gas pipeline and an immediate gas supply cut to the end user.
Also, the supplier would detect a significant pressure drop in their pipelines.
In this case, the supplier confirmed that their gas lines were not damaged and no leak was detected, which again could eliminate this as a possible cause of an explosion.
Lastly, if the concentration of a leaked gas in the air is greater than 15%, a gas ignition would lead to a fire and the affected area would burn to ashes.
In the case of the Joburg incident, there was no fire, which eliminated the latter as a possibility.
How gas ignites
For a gas to ignite, there are three things which are required:
- The fuel, which is a gas being transported through the pipelines;
- Oxygen, which is readily available in the air; and
- A spark, which could be generated by static electricity.
Another interesting detail from the investigation was that Egoli Gas – the company which legally operates the gas pipelines within the vicinity of the affected area – released a statement confirming their pipelines were not damaged during the explosion.
Furthermore, the City of Joburg civil engineer, Johan La Grange, also confirmed in a television interview the city had conducted some gas analysis in the area but could not detect any trace of the gases from the pipelines operated by Egoli Gas.
The company is said to transport ethane through the pipelines located in the area.
The gas analysis report from the city indicates there were some traces of methane, which makes one wonder if there are other gas pipelines in the area which the city may not be aware of.
The main question remains whether a gas pipeline could have caused an explosion in Joburg.
Gas pipelines not damaged
From the latest information available to the public, it appears that the gas pipelines in the area are not damaged and unless some critical information is missing, they may not have caused the explosion.
If the explosion was indeed caused by a gas pipeline, it is most likely to be an inflammable gas.
This could mean there could be some gas pipelines being operated illegally and the city may have no knowledge of.
If the explosion emanated from the gas pipelines, they would have been destroyed, especially in the vicinity of the affected area.
As such, the city has to dig deeper and be as precise as possible in finding answers.
Without that, its competence will continue to be called into question, casting further doubt on its claim as a world-class African city.
*The views expressed in this article are that of the author/s and do not necessarily reflect that of the University of Johannesburg.