a) fire extinguishers

b) buoys

c) insulating flasks

The answer is a. The fire grenade was a popular addition to people’s houses from 1850 and was still in use in the mid 20th century, although there were some changes to its design.

It took the form of a light glass vessel. Early ones were filled with water and salt. The salt would stop the fluid from freezing. When a fire broke out the fire grenade would be thrown at the base of the fire. The vessel would shatter and the contents would cover the fire, cutting off the oxygen supply, and extinguishing the fire.

Later versions of the fire grenade were filled with carbon tetrachloride. This was very effective, but it could cause significant hazards for the user as in certain circumstances chlorine would be produced. Many of these grenades were suspended above a potential source of fire. They would be hung onto a bracket that would be designed to melt in the heat of the fire, thereby delivering the grenade to the source of the problem.

To see examples of these grenades why not try a fire museum or science museum near to you. Some can also still be seen in old houses. However, they should always be handled with care. They are designed to break when dropped and their contents can be nasty.

Sophie Duncan is a physicist and programme manager with Science Year www.scienceyear.com