Preventing entrapment in plastics rotational moulding ovens where there is whole body access

Health and Safety Executive - Safety alert

Introduction

This safety bulletin is being issued following a fatality in a plastics rotational moulding oven.  This information is issued without prejudice to any ongoing investigations.

HSE is using this alert to raise awareness of the issue of whole body entrapment inside rotational moulding ovens and to urge users of these machines to review their moulding machines and procedures to ensure whole body entrapment is not possible through:

• the layout and design of machinery;
• safe working procedures; and
• ensuring a means of escape from the oven is provided.

Background

Rotational moulding ovens are used to melt plastic powders or granules that are placed in a mould, which is then heated whilst being rotated and in some cases rocked. As the plastic melts it coats the inside of the mould to form the product being manufactured. Products being manufactured in this way range from small to very large items. Consequently, the ovens the mould is rotated in can vary greatly in size and some are big enough for whole body access and sometimes have conveying systems to carry the mould into the oven, The introduction of conveyor systems in any oven increases the likelihood of access into that oven in order to carry out either routine or breakdown maintenance on the conveyor system. In addition, as the plastic sometimes drips out of the mould during production there is a need for people to enter the oven to clean the residue off or to enter the oven for other maintenance reasons.

HSE has identified that on some rotational moulding ovens where there is the potential for whole body access there is a risk of entrapment. The consequences of a person becoming trapped inside an oven, which is then heated up, is almost certain death due to the high temperatures that the ovens can reach.

A number of factors are present that contribute to the risk of entrapment as follows:

• Positioning of the control panel – on some machines it was found that the control panel was positioned so the operator does not have a direct line of sight into the oven and therefore could not check in the oven to ensure there was no-one inside before they closed the doors. This situation was made worse if there was more than one door access into the oven.
• Powered locking doors – the introduction of powered locking doors meant that once doors are closed, any person trapped inside the oven cannot get out. In addition, where doors to the oven are powered and closed remotely (via the control panel) then the operator did not necessarily go near the oven to check that it was empty.
• Speed of door closing/locking – some machines had doors that closed very quickly and locked shut.  This meant that if a person was inside the oven they had no opportunity to escape before they were locked in the oven.
• Door closing warning systems – some machines had no door closing warning system.
• Means of escape/raising the alarm/stopping equipment – Most machines had no means of escape or a way of summoning assistance or providing a way of turning off the oven from the inside, despite there being the need for people to enter the oven.
• Safe Systems of Work – In some instances inadequate or non-existent safe systems of work were in place. Often it was found that if a safe system of work did exist it did not include areas such as isolation and oven entry procedures.

Action required

Users of machines with whole body access and the risk of entrapment should now carryout a risk assessment of their machines and procedures to ensure they have adequate control measures in place.  The risk assessment should consider the likelihood of getting trapped inside the oven, how a person could escape if they were trapped and the package of control measures that need to be in place to prevent this.  The factors outlined in this safety notice along with any other relevant factors should be considered as a part of the risk assessment process and the correct combination of controls for your machine should be put in place. Control measures may include:

• Line of sight into the oven - Ensure the operator has a good line of sight into the oven.  This will help the operator to ensure there is no-one in the oven before they close the doors and turn it on.  This is particularly important where there is more than one access door present.  If they do not have a good line of sight then take steps to provide this eg by relocating the control panel or providing other visual aids such as mirrors and CCTV.
• Door closing system - Consider the door closing system and identify if the door speed is appropriate and whether a door closing alarm is needed.  This combination will enable anybody inside the oven time to escape and also to give the operator time to register someone is in there.
• Managing multiple access points into the oven - Where there is more than one access door into the oven there will need to be robust management systems in place to ensure an operator does not become trapped. Sequencing door closing mechanisms, for example, so one door closes first while the operator observes the inside of the oven to make sure no-one enters it before closing the second door may reduce the risks.
• Providing a means of escape - Where there is a risk of entrapment then you will need to consider if a means of escape from the oven should be provided. Measures that can be implemented if a person does become trapped in the oven may fall into one or all of the following areas:
  • providing a means to escape easily eg through kick panels or by a means of opening the door from inside; or
  • providing means to raise the alarm from the inside of the oven to let people know they have become trapped; or
  • means to turn the oven and rotational moulding arm off from inside the oven eg by an emergency stop button that is actuated from inside the oven.

Whatever measures your risk assessment identifies you should ensure they are designed so that a person who is trapped within the oven is able to find and use them, eg if it were dark lighting may be needed etc.

Safe systems of work – when carrying out your risk assessment you should ensure that robust safe systems of work are in place that accurately consider and reflect your machine operation and procedures. The safe systems of work should include, but not be limited to isolation and oven entry procedures. Once established, appropriate information, instruction, training and supervision should be provided to all staff to ensure that the risk of entrapment is controlled.

Relevant legal documents

• Provision and Use of Work Equipment Regulations 1998
• Management of Health and Safety at Work Regulations 1999

References

None

Further information

Health and Safety Executive
OPSTD Manufacturing Sector - Plastics
Foundry House
3 Millsands
Riverside Exchange
Sheffield
S3 8TH

General note

Please pass this information to a colleague who may have this equipment or operate this type of process.