Question- Headers in <figure> & <details> (Techniques for providing useful text alternatives)

Hello,
 
If I understand well, the headers structure in the figure, details
elements is separate and does not belong to the structure of the page. 
However, I wouldn't prefer to have many H1 in one page, For instance: 
 
How would be the order of the headers in Example 2.4
http://dev.w3.org/html5/alt-techniques/ 
if the longer text alternative contains headers? 
—--------
page content...
<h2>Power sources</h2>
<h3>Electrical Power Sources</h3>
     <figure role="group">
     <figcapion> Non-Functioning Lamps</figcaption>
     <img src="flowchart.gif" alt="A flowchart process - Dealing with
non-functioning Fluorescent lamp and Discharge lamp.">
     <details> 
     <summary><strong>Dealing with non-functioning Fluorescent lamp and
Discharge lamp</strong> </summary>
     <h??> Fluorescent lamp</h??>
     <p><strong>If the lamp doesn't work:</strong></p>
     <ol>
      <li>Check if it's plugged in, if not, plug it in.</li>
      <li>If it still doesn't work; check if the bulb is burned out.
      If it is, replace the bulb.</li>
      <li>If it still doesn't work; buy a new lamp.</li>
     </ol>
     <h??> Discharge lamp</h??>
     <p><strong>If the lamp doesn't work:</strong></p>
     <ol>
      <li>Check if it's plugged in, if not, plug it in.</li>
      <li>If it still doesn't work; check if the bulb is burned out.
      If it is, replace the bulb.</li>
      <li>If it still doesn't work; buy a new lamp.</li>
     </ol>
 
     </details>
     </figure>
<h2>Natural power sources</h2>
..rest of the page
—----------
 
Thank you,
Rabab Gomaa