Knock knock

Fire doors with powerful springs to keep them closed are a major problem when users have both arms full of files, shopping or cups of tea. In many offices, they end up being wedged open, which completely negates their function as fire doors. Do away with the powerful spring and they become ordinary doors. It is possible to come up with a mechanism that is normally free to move yet activates a strong closing force when a fire is detected but that still leaves problems when they are free to move. There is also a potential hazard if somebody is passing through the door if it suddenly starts to close. If doors are free to open and close, on the other hand, but are not carefully hung, they can easily drift open or slam in a draught. This is annoying in most homes, but even more so in a care home for the elderly, and an irresistible source of major sound impulse in the hands of teenagers. The Challenge Our challenge this month, therefore, is to come up with a door closing mechanism that closes firmly in the event of a fire, without risking the health and safety of anyone passing though it at the time, yet in normal use, is easy to open and close with minimum force. Yet, at the same time, it should not be possible to slam it, in the hands of either angry teenager or an elderly person suffering from dementia. The real answer, is, as in royal palaces when monarchs held real power, to have doors opened and closed by flunkeys. About the only place where there is a door that always has somebody available to open and close it at the present time in the UK is Number 10 Downing Street, but that is not a facility available to most of us. It is possible to have doors that open and close when they detect humans. An increasing number of shops and institutions have them. Apart from the cost, they do have the tendency to open when somebody stands near them, who happens to not want to pass through the door, so an ideal control system, would have to respond to either the voice of the user, or detect their intention in some way. The alternative is to have something clever but simple in the door closing mechanism. We do happen to know of one that solves the problem most elegantly, making use of traditional British engineering technology principles, which we will describe fully in our next edition. It works reliable and is patented. See if you can come up with anything better.