SCENARIO

You work as a farm manager for a large commercial farming organisation. The farm where you

normally work mainly grows cereal grains and is located in a rural location near to the coastline.

Once harvested, the cereal grains are loaded into cylindrical steel silos by conveyor. The conveyor

discharges the grain into the silo at the silo’s highest point. The grain is then dried over a period of

weeks by blowing dry air through the grain from the base to the top of the silo. When the grain is dry,

it is discharged from the bottom of the silo by a screw conveyor. The screw conveyor collects the

grain and transfers it onto another flat-bed conveyor. This flat-bed conveyor moves the grain from

beneath the silo onto a waiting truck.

Your farm has 4 grain silos. Each silo is 15 metres high and has a diameter of 9 metres. There is an

inspection hatch/door at a height of 2 metres that is large enough to allow a person to gain entry. A

metal step allows access to this door. All the grain silos are approaching the end of their design life.

Recently, workers at your farm have reported reduced grain flow from one of the silos. You visit the

silo to find out what the problem is and suspect there is a partial blockage. Other farms within the

organisation have reported similar issues. You decide to close the silo for investigations once all the

existing grain has been removed.

You explain the problem to the farm’s maintenance engineer, who says that the maintenance team

will conduct a preliminary inspection of the silo. The maintenance engineer tells you that there is

often a build-up of fine grain, dirt and other debris at the bottom of the silo and this can cause

problems with the operation of the screw conveyor. Some of the grain could have been there for

some time and could have become compacted and damp. This encourages mould growth and

makes the emptying problem worse.

Following the visual inspection, the maintenance engineer reports back that the screw conveyor is

damaged and that the vents and roof hatch do not close properly. They also report extensive metal

corrosion to the inside surface of the silo. The recommendation is that the silo should not be put

back into service until repaired, but before this can happen the silo needs to be thoroughly cleaned

inside. This will need a team of three maintenance workers who have worked together before and

consist of a supervisor (55-years-old who has mild asthma), and two other workers (a 17-year-old

apprentice and a newly recruited 28-year-old).

It is likely that the work will take up to a week to complete and will be carried out in the summer

months when the weather can be very hot and humid. The maintenance engineer advises you that

they will complete a risk assessment of the silo cleaning and repair, and will send this to you for

review before any work starts.

Task 1: Confined space risk assessment

1 (a) What should you consider when assessing the risk from carrying out the grain silo cleaning operation?                                                                                                                                       (20)

(b) How could you control the risks before and during the cleaning of the silo?                          (20)

Note: You should support your answer, where applicable, using relevant information from the scenario.

Task 2: Typical cause of failures

2 Based on the scenario, what could have contributed to the extensive metal corrosion to the inside surface of the silo?                                                                                                                         (15)