Unconfined vapour cloud explosions (UCVEs) in a semiconductor foundry can pose a severe threat to personnel, resulting in casualties and costly damages if left unchecked.
As such, it is of utmost importance for personnel working in a semiconductor foundry to be aware of the basics of UCVEs - what they are, how they occur, why they occur but most importantly, how they can be prevented.
This article will cover what constitutes a UCVE and several preventative measures that may assist to mitigate its devastating effects.
What is a UVCE?
UVCE is a type of explosion that occurs when a cloud of flammable vapour mixes with air and is ignited within a vast foundry space.
The sequence leading to a UVCE typically involves the release of a flammable gas or vapour, its dispersion within the foundry space and its subsequent ignition.
When these vapours mix with oxygen present in the foundry space, they can form an explosive mixture capable of releasing large quantity of energy when ignited.
UVCEs are particularly dangerous because explosions can occur far beyond the original point of release
This energy then propels and spreads rapidly, resulting in a powerful explosion that may devastate anything in its blast sphere.
UVCEs are particularly dangerous because explosions can occur far beyond the original point of release due to vapours being carried by air movement inside the foundry space.
It means a UVCE has the potential to travel vast distances in search of ignition sources, resulting in a much larger blast sphere and increased destruction.
What are the factors that contribute to a UVCE in a semiconductor foundry?
Many factors can contribute to a semiconductor foundry’s UVCE. Listed below are several factors that can contribute to a UVCE and should be considered when working in hazardous environments.
- Poorly maintained equipment such as pipes, tanks, valves and hoses et cetera
- Excessive temperature and/or pressure inside a tank or pipe
- Ventilation and air handling systems poorly designed and/or constructed are ineffective to prevent the accumulation of hazardous vapours
- A lack of preventive measures that can limit the size and scope of a UVCE, such as gas leak detection system, spark detection system, fire retardants and flame arrestors
- A lack of proper storage and handling procedures to minimise potential risks
- Poor housekeeping practices that increase the likelihood of ignition sources such as static coming into contact with flammable vapours
- Untrained personnel handling flammable chemicals or personnel failing to adhere to safety protocols
- The presence of vapour with gas/oxygen mixture between the lower flammable limit (LFL) and upper flammable limit (UFL)
What are the potential consequences of a UVCE?
The consequences of a UVCE can be devastating, resulting in massive destruction and possibly loss of life. Blast wave from a UVCE may result in severe property damage and fires are ignited due to the burning gases/liquid mix released during the explosion. There are three possible pathways that a blast wave from an UVCE can cause injury to nearby personnel, namely:
Pathway 1 - direct transmission of blast wave through body tissue, resulting in compression of organs. Lungs, ears, abdominal and brain may be affected.
Pathway 2 - due to fragments accelerated by the blast wind. Fragments may penetrate the eyes, puncture lungs and other organs.
Pathway 3 - related to the possible displacement of the body and/or possible displacement of objects that interact with the body.
Toxic fumes such as carbon dioxide are also released into the foundry space.
It was reported that a carbon dioxide level at 100,000 ppm was the atmospheric concentration immediately dangerous to personnel in the vicinity and that exposure to 100,000 ppm for only a few minutes may cause a loss of consciousness.
Given these potential consequences, it is essential for personnel operating in hazardous environments to be aware of preventive measures that can help mitigate the effects of a UVCE.
How to mitigate a UVCE?
There are several steps that personnel and plant operators can take to help prevent the occurrence and reduce the severity of a UVCE. These include:
- Conducting plant hazard CFD simulation to reveal and identify hidden hazards
- Conducting CFD simulation on various flammable gas leak scenarios to predict the severity and impact to the immediate surrounding
- Design the facility with proper isolation and containment measures to prevent the spread of vapours. Use barriers, enclosures and physical barriers to contain potential releases
- Ensure the ventilation and air handling systems are correctly operated and regularly maintained which will help to prevent the buildup of any hazardous vapour
- Ensure the handling, storage and disposal of hazardous materials are performed according to the standard operating procedures (SOPs)
- Ensure operators or personnel handling flammable chemicals have undergone proper safety trainings or courses
- Conducting a thorough safety analysis such as failure mode effects analysis (FMEA) before implementing a new task
- Implement measures to control and eliminate potential ignition sources. This includes using inherently safe equipment and ensuring proper grounding/earthing of equipment and vessels
- Use explosion-proof electrical and mechanical equipment to minimise the risk of ignition sources
- Regularly inspecting pipes, tanks, valves et cetera, for any sign of wear and tear or damage
- Installing flame arrestors, spark detection systems and other preventive measures to limit the size of a fire/explosion in the event of a UVCE
- Install gas detection systems to continuously monitor for the presence of hazardous vapours. These systems can provide early warnings and trigger alarms if concentrations exceed safe levels
- Regularly testing safety equipment (fire extinguishers, ventilation systems, etc.) to ensure they function properly
- Implementing strict housekeeping rules, such as no smoking or open flames near combustible materials and using spark-resistant tools whenever possible
- Utilising pressure relief devices to prevent over-pressurisation of containers which in turn will reduce the risk of the release of vapours
- Installing fire suppression systems to quickly detect and extinguish any combustion in the event of a UVCE
By taking the right steps, personnel and plant operators can help protect their semiconductor foundry from the devastating effects of a UVCE.
For those working in hazardous environments, it is essential to be aware of the potential consequences of a UVCE and the preventive measures they can undertake to protect the foundry and personnel.
By implementing the right protocols and preventive measures, personnel can help reduce the risks associated with a UVCE.
What can personnel do in the case of UCVE?
If a UVCE occurs, personnel and plant operators should take immediate steps to minimise damage. These steps include:
- Immediately shut off all sources of ignition in the affected area
- Activate emergency protocols such as evacuating personnel, activating fire suppression and Desmoke systems
- Employ appropriate safety measures such as wearing protective clothing and respiratory system when entering the affected area
- Seal off the affected area to prevent the spreading of toxic gases and vapours
- Work with local fire and rescue personnel to ensure the area is safe before attempting any repair or clean-up
By taking the right steps, personnel can help minimise the damage caused by a UVCE and protect personnel in the affected area.
Conclusion
The risks associated with a UVCE are real. Nevertheless, a semiconductor foundry can ensure that their personnel and facilities remain protected by implementing proper safety procedures and preventive measures.
By understanding the potential consequences of a UVCE and taking the necessary steps to minimise if not to prevent them, personnel can help ensure foundry and personnel remain safe from harm.
Ultimately, the best way to protect against a UVCE is to be proactive and take the necessary measures to identify, address and eliminate any potential risk before an incident occurs.
