IEC Standard

To start your requirement is a bit weak.

Normally you ask for equipment which is approved to be mounted in a certain classified zone.

Typically you will specify whether it is for mining or surface applications, the type of risk you have (dust or gas) the severity of risc (the likelihood that an explosive atmosphere is present) and a temperature classification (at which temperature of a surface your flammable mixture will ignite)

I know that in old requirements they typically tend to specify the method of protection but in the modern world this is not done anymore.

Get your zone classification, someone once did this as the requirement for Eed has been specified.

Ask the suppliers to quote for a pump to be used in the specific zone.

Discuss the quotes with the authority having jurisdiction in your typical application (mostly the same organisation/person who give you the zone classification) and let them specify which solution is the best fit for the job. In the end they are legally responsible and will have to approve the decision anyhow, just take them along in the decision making process.

In the same run you will learn a lot of explosion prevention and next time you have to do something it will go easier and with less questions.

So the first thing you will have to solve is: who the hell is the authority having jurisdiction, a good starting point is the prevention officer, he must be able to tell you this.