When Louisa smashes the pane in Mrs Cronk's door to get in, she knocks out about 1/3 of the glass in that pane and reaches through to open the door. When she opens the door, it appears that all the glass in that pane has gone, but as the door continues to move the remaining glass can still be seen momentarily.
While Peter is wearing the oxygen mask, it constantly fogs up and the reservoir bag doesn't inflate, indicating little or no oxygen flow. Such a mask requires 10-15 liters per minute of oxygen flow.