Tank Ventilation | Safety in Explosive Atmospheres & Confined Spaces

Published 20 Jan 2020

Tank Ventilation in Explosive Atmospheres

Special thanks to Tank Storage Association (TSA) for sharing the Editorial

Terry McDonald, Thorne & Derrick International, UK, and Scott Harding, Woodcock & Wilson, UK, outline the importance of using safe equipment for tank ventilation in explosive atmospheres.

There are many hazards associated with work activities carried out inside of storage tanks, such as flammable atmospheres, chemical exposure, toxic risk, and oxygen deficiency. These risks can and do cause serious injury or death.

This article will focus on tank ventilation and the associated risks of using ventilation fans in an explosive
atmosphere. It will specifically discuss electrical and non-electrical safety within explosive atmospheres. It is widely accepted that electrical knowledge and understanding of regulations throughout the industry is good, but non-electrical knowledge is poor and learning is a slow process.

This article serves to provide information relevant to electrical and non-electrical safety standards and regulations to anyone using portable ventilation fans in an explosive atmosphere.

When working inside tanks, an efficient ventilation system is critical. Safe working procedures dictate that a tank should be properly ventilated and/or forced ventilation should be used to ensure the tank is safe prior to man e try. There have been many accidents and fatalities caused by people entering tanks/confined spaces when it is not safe to do so. Breathing one or two breaths of air containing oxygen levels below 10% can cause immediate loss of consciousness.

The safe use of portable ventilation fans can be an area of particular confusion when they are being used in a
potentially explosive atmosphere. They are essentially a mechanical piece of equipment, which is electrically
powered. It is important to ask a number of questions, including the following:

Which standards should be considered?
Who is responsible for ensuring compliance?
Who is responsible for maintenance?
How often should the equipment be inspected?
Is a competent person required to install/use such equipment?
Who takes responsibility for ensuring any equipment is compliant with explosive atmosphere regulations?

In the Dangerous Substances and Explosive Atmospheres Regulations (DSEAR), an explosive atmosphere is defined as a mixture of dangerous substances with air, under atmospheric conditions, in the form of gases, vapours, mist or dust in which, after ignition has occurred, combustion spreads to the entire unburned mixture.¹

In Europe, explosive atmospheres are regulated under the ATEX directive. ATEX 2014/34/EU is the latest standard
and was originally launched in 1996. It became mandatory in July 2003 within the EU. Its purpose is to protect
employees from explosion risk in areas with a potentially explosive atmosphere.

These directives place responsibility on the original equipment manufacturer (OEM) and the ultimate end user to ensure safe and proper use of any equipment which is to be used within a potentially explosive atmosphere. The ultimate end user is considered to be the duty holder/site owner on which the equipment will be used.

Explosive atmospheres are classified dependant on the likelihood of risk, for gases, vapours and mists, these are
defined as follows:

Zone 0 – a place in which an explosive atmosphere consisting of a mixture with air of dangerous substances in the form of gas, vapour or mist is present continuously or for long periods or frequently

Zone 1 – a place in which an explosive atmosphere consisting of a mixture with air of dangerous substances in the form of gas, vapour or mist is likely to occur in normal operation occasionally

Zone 2 – a place in which an explosive atmosphere consisting of a mixture with air of dangerous substances in the form of gas, vapour or mist is not likely to occur in normal operation but, if it does occur,
will persist for a short period only.²

Under the ATEX equipment directive, manufacturers of electrical equipment designed for use in Zone 1 hazardous
areas, must obtain third party certification from a notified body. This process involves stringent testing procedures
and technical review to ensure that the product is safe for use in an explosive atmosphere. Although not a legal
requirement, manufactures more often than not also obtain third party certification for Zone 2 electrical equipment.

However, under current ATEX regulations, manufactures of mechanical equipment can self-certify for both Zone 1
and Zone 2. To self-certify, an OEM has to lodge a technical file with a third party notified body. The notified body does not have to read the file and the file may never be looked at unless there is a subsequent problem/failure/accident with the piece of equipment.

There are many advocates of self-certification and there are occasions when there is no other option. Thorne
& Derrick International (T&D) would suggest that self-certification of any equipment should at least raise a doubt
in the mind of the ultimate end user. It is worth pointing out that any manufacturer of such equipment must take
their responsibility seriously and the majority do. But questions can be raised as to whether there is a conflict of
interest when a profit making, commercially driven organisation is permitted to self-certify its own equipment.

Without third party testing and certification, how can the end user ever be 100% satisfied? It is also worth
commenting that some manufactures knowledge and understanding of the regulations can be questionable.

While their electrical knowledge may be good, their mechanical knowledge may not. T&D has seen examples of
end users accepting a piece of equipment because the electrical motor is third party certified. A third party
certificate is issued, which the end user accepts, but the certificate only covers the motor not the product. Has
spark mitigation been considered? What about electrostatic discharge? Has the manufacturer considered this? Has the end user considered this?

Ventilation fans are also unique in that fans have their own specific standard ‘EN14986-2017 – Design of Fans
Working in Potentially Explosive Atmospheres’. There is no doubt that there will be people reading this article who are not familiar with the standard or know that it exists.

Before any piece of equipment is used in a hazardous area, it should be inspected by a competent person to ensure that it is fit for purpose and compliant with the full hazardous area classification (Zone, gas group, T-class, ambient temperature range). This normally involves a review of certification and the associated certificate of compliance.

But here lies the problem: this relies wholly on the knowledge of the person carrying out the inspection and places too much reliance on the certificate of conformity.

Does every inspector know that EN14986-2017 exists? When a portable ventilation fan is being inspected, is it
considered an electrical piece of equipment or a nonelectrical piece of equipment? What If EN14986 is not referenced on the certificate of compliance, how will the inspector ensure compliance?

It is often the case that inspectors are electrically biased and have excellent electrical knowledge and understanding of the electrical standards. Unfortunately their non-electrical knowledge may not be as good.

To further complicate matters and increase risk, portable ventilation fans are often hired for the duration of
a contract. The supply chain can involve OEM, distributor, reseller, hire company and contractor before the product is placed into use on site. This relies on the contractor’s knowledge and expertise, as well as that of the hire
company, to ensure the products they are bringing into their hire fleet are compliant.

Are such companies aware of difference between third party certification and self-certification? Allowing self-certification for mechanical equipment means there has to be too much trust placed on the supply chain and that each company carrying out their own due diligence at each stage is capable of doing so. This may not always be the case.

ATEX Fans

When it goes wrong

Figure 1 shows the catastrophic failure of an impeller on a fan which was in use within an explosive atmosphere. The manufacturer’s documentation issued with this fan read:

“Please note that under ATEX directive, it is the responsibility of the purchaser/installer to ensure compliance with ATEX directives and ensure safe operation of the unit. We are unable to accept liability for the design and specification of the product in its intended application.”

This statement puts the risk entirely with the end user and essentially negates the manufacturer from any responsibility.

Figure 1. Damage as a result of a 90 kW motor failing at 1450 rpm.

There are examples of fans that make no reference to the fan standard on their certificate of compliance, and it is
also possible that some ventilation fans may use fraudulent certificates. This is much more serious and obviously a
criminal offence. Again, it relies on the buyer of such equipment having the knowledge and expertise to question a certificates legitimacy.

IECEx vs ATEX

IECEx is an international certification scheme for electrical and non-electrical equipment. It is a voluntary scheme that provides an internationally accepted means of proving compliance with IEC standards.³

Self-certification under the scheme is strictly prohibited; manufacturers must be audited by an IECEx
notified body. The manufacturer’s quality procedures and facility are reviewed before a quality assurance report
(QAR) is issued. The equipment requiring certification is then tested/reviewed by the notified body against relevant international standards. An IECEx Certificate of Conformity is issued after successful assessment.

The IECEx scheme is arguably more transparent from an end users perspective. The certificate of conformity is
available to view on the IECEx website/database. The means the end user can quickly check and establish the
quality credentials of the OEM. It also means unscrupulous manufacturers cannot issue fraudulent certificates.

Within the EU, IECEx is a voluntary scheme rather than mandatory as with ATEX. As time moves on, more and more UK and EU specifications are requesting dual certification (ATEX & IECEx) for equipment.

Figure 2. The world’s first ATEX and IECEx certified

Conclusion

Although this article focuses on ventilation fans, the same regulations and said drawbacks of these regulations apply
to any equipment that is to be used in an explosive atmosphere. T&D would urge all end users/dutyholders to carefully consider their full supply chain. They should also continue to improve their own knowledge and understanding of electrical and non-electrical standards.

References

1. ‘The Dangerous Substances and Explosive Atmospheres
Regulations’, Health and Safety Executive (HSE), (2002).
2. ‘Explosive Atmospheres – Classification of Hazardous Areas (Zoning) and Selection of Equipment’, Health and Safety Executive (HSE).
3. https://www.csagroupuk.org/services/ex-product-certificationapprovals/iecex/

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