Container top safety frames

SIM 05/2008/05


This SIM updates and replaces SIM 05/2003/56 and offers inspectors guidance on the issues to consider during the inspection of container top safety (CTS) frames and the associated training and systems of work. Much of the guidance will also be applicable to other types of frame such as "Torpedo" and "Stinis" frames.

The guidance was written specifically for gantry cranes. Although many of the principles will apply to the use of CTS frames with slewing cranes, inspectors may wish to seek further advice from the sector on specific issues arising in these instructions.


1 Loading and unloading containers from ships usually involves access to the tops of container stacks to remove and place the securing devices holding the stacks together (known as twist locks).

2 Containers are normally around 3m tall and stacks can be up to 5 containers high above the deck of a ship. Despite the obvious risk of falling container operations were, traditionally, carried out by stevedores walking across container tops. This work was often carried out with no fall prevention methods. When fall prevention was provided it was in the form of a harness. This method sometimes had significant problems as access to suitable anchor points was difficult.

3 There are a number of methods for reducing the risk of falls when working on containers. Information on these systems and their relative merits can be found in international guidance (see 'Further information' below). The use of one of these methods, namely CTS frames, is increasing and this SIM deals with the specific issues arising out of the use of these frames.

4 CTS frames are cages suspended from a container crane in which workers are carried to and from the container stack and from which work on the stack can take place. They are usually the size of a container, with an enclosed roof and open sides with hand rails. Contact with the crane driver is by radio and/or hand signal. Many operations which previously required personnel to walk on container tops can be carried out from within the frame.

5 CTS frames usually operate above containers and access to twist locks is gained through flaps in the floor. The frame is designed for continuous motion over the container stacks usually working from sea to quay across the ship. Operators will stoop or kneel on the floor of the frame for these operations. Such operations are carried out over stacks of containers which are all the same height.

6 There are times, however, when the frame will be adjacent to rather than above containers and other fixed objects. If the frame is in motion, under these circumstances, there is the potential for any part of the body which is outside the frame to be trapped or crushed. One worker has been killed in this way.

7 In particular, there are times when the frame will be used beside other stacks of containers to undo twist locks etc. Examples include occasions when an adjacent stack is to stay on the vessel and go to another port (such containers are known as "remain on boards") or when adjacent container stacks have "over height" containers in them (containers which are taller than the standard version). There may also be the need to work beside container stacks to free jammed twist locks. These types of operation must only be attempted with the frame stationary.

8 To reduce any trapping risk to a minimum the use of CTS frames must be subject to an adequate risk assessment which should consider both the frame and the tasks that will be carried out from it. This will include consideration of the frame design, an adequate safe system of work and the training required by staff. The results of the assessment should be implemented, monitored and reviewed.

9 A good design together with a safe system of work and adequate training will help reduce the risk from container operations eg by minimising the need to work outside the frame.

Design of frames

10 The following issues should be considered for during a risk assessment for a CTS frame:

  • The provision of a top and intermediate handrail and toe boards (toe boards can only be fitted along the longest sides). The top rail should be about 1100mm high.
  • Frames will operate up to 50m from the ground, often in windy and wet conditions. The rails and toeboards must be adequate not only to prevent the personnel in the frame from falling out but also to protect those working below (eg from falling twistlocks).
  • The top rail should be colour coded (eg fluorescent orange and black stripes) to ensure it stands out from the rest of the frame. Frames will be used at night and in the fog and any paint must be suitable for this purpose and ensure that operators can quickly find the rail (eg to hold onto when the frame is in motion or sways in the wind).
  • The rails should be recessed by about 90 mm from the edge of the frame to reduce any finger trapping hazard if the frame strikes an adjacent container whilst in motion.
  • In the floor at the ends of the frame there are lift up flaps together with a knee rail. The rail allows operators to brace themselves as they reach through the flap. Toeboards cannot be fitted on the short sides as it interferes with the frame's operation.
  • The provision of mesh from the toeboard to the top rail. Additional meshing beyond this may have the negative effect of encouraging operators to work outside the frame as it could significantly reduce the versatility of the frame and hamper the use of hand signals.
  • Storage boxes for twist locks at each corner of the frame to ensure they are not loose and become a tripping hazard or fall through the flaps in the floor
  • A non-slip floor that quickly sheds water in adverse conditions.
  • Recessed access gates (again by 90 mm) to allow safe access and egress from the frame on occasions when this becomes necessary
  • A safe area for operators to stand whilst they are not working and the frame is in motion. Such an area must be designed to ensure that operators are not likely to be thrown about by the motion of the cage particularly when it is breezy. If seats are provided they must protect the operator from injury should the frame be set down onto the stack with a jolt.
  • Tested harness anchor points. Operators must clip on when exiting the frame or when leaning out of the frame. The frame itself becomes the anchor point overcoming previous difficulties of finding such a point in traditional systems of work.

System of work

11 There must be a written safe system of work in place covering the operation of these frames. It will usually need to cover (but not be limited to):

  • Staffing eg two operators and a signaller.
  • An instruction to users to ensure that all body parts are within the frame whilst it is moving (except for access to container tops through the flaps in the floor). Most frames are designed so that there is a large open space above the top rail for the reasons given above. The adherence to the SOW is a critical risk reduction measure whilst the frame is in motion.
  • Supervision and signalling arrangements for frame users including details for ensuring the frame is not moved until personnel are in positions of safety.
  • The operations which can only be carried out whilst the frame is stationary
  • Access from the frame to container tops including use of harness. Operators will need to understand that the frame is the preferred access method and will need guidance on the (limited) circumstances when they can work outside it.
  • Arrangements for monitoring and review.
  • Emergency arrangements (including instructions to remain in the frame during a crane breakdown).


12 Training is an essential part of CTS frame safety. Prior to any training employees must be assessed as being physically fit, as this is a heavy manual job. They must also have an ability to work comfortably at height.

13 Training must include a significant practical element which is carried out under close supervision preferably on a training rig to begin with. Following training, a competence test should be undertake by all trainees. Both training and competence assessment must cover the full range of operations carried out using the frame.

14 Training must include full details of the safe system of work and measures in place to protect employees using the frame.

15. It is good practice for trainees to be identified (eg by wearing different coloured safety helmets).

Relevant legislation

16 The legislation which applies is:

  • The Health and Safety at Work etc Act section 2, which covers the provision of safe plant, safe systems of work and training as far as is reasonably practicable.
  • The Lifting Operations and Lifting Equipment Regulations 1998, in particular regulation 5 (lifting equipment used for lifting people) and regulation 9 (thorough examination and inspection).
  • The Management of Health and Safety at Work Regulations 1999 regulation 3 (The requirement to undertake a suitable and sufficient risk assessment).
  • The Provision and Use of Work Equipment Regulations 1998, especially regulation 4 (suitability of work equipment) and regulation 9 (training).
  • The Work at Height Regulations 2005


17 The likelihood of a serious or fatal accident in a well-designed and operated CTS frame should be remote. Significant shortcomings in the frame design, systems of work and training when assessed against the criteria in this SIM will quickly increase the risk gap. Where inspectors find frames that are not being operated in accordance with a written SOW, where staff are untrained or where the design or condition of the frame has significant inadequacies a prohibition notice should be considered.

Further information

18 For further information on the issues raised in this SIM contact the STSU Transportation Section in East Grinstead on 01342 334261.

19 Further information can also be found in PSS's Health and Safety in Ports Guidance Sheet SIP003 - Guidance on container handling and in the International Cargo Handling Co-ordination Association (ICHCA) document "Guidelines for lifting persons at work for cargo handling purposes in the port industry".

Action by inspectors

20 Inspectors are asked to:

  • Apply the standards in this SIM when examining operations from CTS frames
  • Advise the STSU Transportation Section of any problems using this SIM.

Cancellation of instructions

21 Cancel and destroy SIM 05/2003/56.

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Updated 2020-12-15