Today's first witness, Bernie Brankin, is sworn in.

A long-serving civil servant, she was head of the finance branch within the finance division of DETI, and you can find her written witness statement to the inquiry on its website, external.

Image source, RHI Inquiry

Junior counsel Joseph Aiken runs through the Byzantine structure of DETI and its finance and energy divisions.

It appears we can look forward to a blizzard of internal emails in this witness session.

BBC News Northern Ireland

The civil servant who effectively ran the RHI scheme on his own said no extra staff were made available to help, even though he flagged up the shortage as a critical risk.

Image source, Pacemaker

DETI official Peter Hutchinson worked on the scheme's set-up and raised his concerns, but nothing came of them.

The inquiry also heard that he had been nominated for bonuses because he had been working hard for log hours to set up the scheme.

BBC News Northern Ireland

An independent inquiry into the RHI scandal was established in January by the then finance minister Máirtín Ó Muilleoir.

He ordered it in the wake of the huge public concern and what was then a developing political crisis surrounding the scheme.

Image source, Pacemaker

The RHI Inquiry began last month and Sir Patrick Coghlin (above), a retired Court of Appeal judge, is its chair and has been given full control over how it will operate.

It will look at:

• the design and introduction of the RHI scheme
• the scheme's initial operation, administration, promotion and supervision
• the introduction of revised subsidies and a usage cap for new scheme claimants in 2015
• the scheme's closure

For more information on the RHI Inquiry, you can read our handy Q&A.

When the scale of the overspend emerged, public and political concern rocketed.

As the minister in charge of the Stormont department that set up the RHI scheme, the Democratic Unionist Party (DUP) leader Arlene Foster faced calls to resign from her role as Northern Ireland's first minister in December last year.

Image source, PA

She resisted, and Sinn Féin's Martin McGuinness then quit as deputy first minister in protest at the DUP's handling of what had by then become a full-blown political crisis.

That move brought about the collapse of the Northern Ireland Executive, and as we near a year on from that Northern Ireland remains without a devolved administration.

If you want a bit more detail on the background to the scandal and the subsequent inquiry, here's our need-to-know guide on the RHI scheme.

There were critical flaws in the way the RHI scheme was set up that left it open to abuse and that later saw its budget spiral out of control.

Crucial cost curbs that existed in a similar scheme in Great Britain were not replicated and claimants could effectively earn more money the more fuel they burned.

That was because the subsidies on offer for renewable fuels were far greater than the cost of the fuels themselves - the scheme was later nicknamed "cash-for-ash" for that very reason.

As a result, the scheme racked up a huge projected overspend - £700m at the most recent estimate, if permanent cost controls are not introduced - and the bill will have to be picked up by the Northern Ireland taxpayer.

Need a quick refresher on what the RHI scandal is all about? Here goes...

The Renewable Heat Incentive scheme - or RHI for short - came to the fore of the Northern Ireland public's knowledge in autumn last year... and the fallout from the scandal attached to it is still being felt in the region's politics today.

Image source, Getty Images

The scheme was set up by the Northern Ireland Executive in 2012, as a way of encouraging businesses to switch from using fossil fuels to renewable sources for generating their heat.

Those who signed up were offered financial incentives to buy new heating systems and the fuel to run them.

Welcome to Stormont for another day on the red benches of the Senate chamber and more of our live video and text coverage of the RHI Inquiry.

Image source, Press Eye

We have two witnesses lined up for today - first up is Bernie Brankin, who was head of the Department of Enterptrise, Trade and Investment's (DETI) finance branch when the RHI scheme was being set up.

This afternoon we'll hear from Mike Brennan, an official from the Department of Finance, who appeared briefly last week.