TECHNICAL GUIDELINES
THROWING CAGES - SAFETY CAGESTRACK AND FIELD FACILITIES MANUAL, CHAPTER 6.3 - EQUIPMENT FOR
THROWING EVENTS – UPDATE 2020
(In addition to the Technical Rule requirements, special requirements are detailed here.)
6.3.2

SAFETY CAGES

Hammer and discus shall only be thrown from an enclosure or cage to ensure the safety of spectators,
officials and athletes. (Figures 2.4.1.2 and 2.4.2.2) The maximum danger sectors and the theoretical way
of calculating these danger sectors for discus and hammer throws are shown on these figures. The same
principles can be used to compare the effectiveness of different cage configurations and how the cages
on the side closest to the implement release may restrict the implement, particularly the hammer, fromlanding within the landing sector.
Cages specified here are intended for use in major stadia in high class competition when the event takes
place outside the arena with spectators present or when the event takes place in the arena and otherevents are taking place at the same time. Simpler and smaller cages may be adequate for competitionof lower standard and for well-regulated training facilities.
Every competition and training venue should have danger zone diagrams prepared and displayed at thevenue for each of its throwing facilities so that the facility manager, the technical officials and/or
coaches are aware of the dangers and schedule events and training accordingly, as well as take normal
safety precautions.
Advice is available from national federations or from the World Athletics Office.
Hammer cages may also be used for Discus Throw competition either by installing 2.135m/2.50m
concentric circles (Figure 6.3.2) or by using an enlarged Hammer cage design but with a Discus circle
installed in front of the Hammer circle. This latter construction is not recommended because of the cost
involved, the space requirements and the effect on viewing.
The design of cages and in particular the gates in the case of a Hammer cage can be innovative provided
that they give the same degree of protection as a conventional design and the relevant danger zone is
not increased. The number of supporting posts may be reduced provided that the netting at the sides
and to the rear of the circle is not closer than shown in Figure 6.3.2. This also means that if the gate
netting pivot point is 4.2m from the centre of a combined discus hammer circle with 3.2m wide gatesthen in the discus throw configuration the gate netting should be parallel with a 6.0m wide opening not
as shown in the Technical Rules. It is permissible for the near side gate to be drawn aside as shown forhammer throwing in Figure 6.3.2 for discus throwing.
The gates should be constructed so that they can be quickly moved during competition. The netting
on gates of metal construction shall be hung at least 0.6m clear of the metalwork.
The nets, supporting structure and the footings shall be designed by a professional structural engineer
to withstand a design wind speed commensurate with the proposed use with a minimum factor of safety

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against overturning of 2 for cages with in-ground footings and 4 for free-standing cages. If a cage is tohave the netting remain in place, then it should be designed for the 1 in 50 years maximum wind gustfor the locality in the direction that creates the maximum load on the cage component. Where necessary
geotechnical advice on the site conditions shall be obtained.
Manufacturers shall disclose the design wind speed to purchasers and in their documentation noting
also the soil conditions for which the footings have been designed. When in doubt professional
engineering advice should be sought. In addition, the design wind speed together with cage model
number shall be indicated on an engraved plaque affixed in a prominent location on a post.
The whole construction, including handling equipment, shall be designed so as minimise the possibilityof an implement striking a hard surface by suspending the netting well clear of supports and padding
hard surfaces where necessary.
The centreline from the circle centre to the centre of the cage mouth must correspond with thecentreline of the landing sector. Therefore, the orientation of the cage must be agreed with local
technical officials before the cage footings are set out. Also, the orientation must ensure, as far aspracticable, that the limits of the danger zone taking into account implement skidding do not reach theoval track or other field event sites.
Manufacturers should provide detailed setting out drawings and installation instructions, including
footing designs, maintenance and operation instructions for the cage including the gates, net tensioning
and anchoring.
The leading edge of the ends of the netting should remain vertical during windy conditions.
The desirable properties of any safety cage are the following:- The cage structure and the netting meet the dimension requirements of the World Athletics
Rules*.
- The netting cord must be strong enough so that it does not break under the impact of theimplement, abrade where it is attached or deteriorate unduly under the effects of ultraviolet ray
exposure*.
- The net can be quickly raised and lowered*.
- There is positive attachment of the netting at ground level which maintains the net in correct
relationship to the throwing circle(s) particularly in windy conditions and there is sufficient
netting at ground level so that an implement cannot penetrate under the netting (preferably aminimum of 30cm adequately anchored).*- The netting when blown by wind does not impede the athlete making a throw (at no time should
netting be tied to the cage superstructure).*- The gate pivot posts and any gate metal frame should not be exposed so that it can be hit by
an implement causing damage to both.

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- The netting shall be hung clear of the support posts by at least 0.60m and arranged so when
the gate is closed that the posts are not struck by a thrown implement*.
- The volume of netting needs to be sufficient to minimise rebound of implements but not slack
enough to allow implements to push netting against the supporting structure.*- The gates shall be easy to open and close manually quickly with a positive positioning
arrangement in the fully open and closed positions.
- The leading edge of the gate netting must maintain a vertical line in order to maintain the
integrity of the danger zone. This means that a tensioning of the leading edge will generally berequired at each anchor point i.e. open and closed position.*- The gates shall maintain their integrity under long term usage.
- The supporting frame shall be stiff enough so that it does not deflect out of position unduly
under the weight of the net and the force of wind*.
- The cage should be easy to install and remove preferably without heavy lifting equipment*.
- The cage structure should not unduly block the spectator view of the track events when the
netting is lowered*.
- Maintenance procedures required to maintain the safety of cage before, during and after
competition must be provided. The users and maintenance staff should be regularly remindedof these procedures*.
* These properties also apply to a stand-alone discus cage.

6.3.2.1 Necessary Safety Precautions
National safety regulations may require tests in addition to those listed. However, the following are
considered to be the minimum safety tests and requirements:- Careful and regular check of all materials, joints, bolts, lifting mechanisms and supports before
each competition season.
- Inspect netting and repair, if necessary, before each competition.
- Test netting materials at least once per year.
If fibre netting is used, several sample lengths, minimum 2 metres long, or several sample mesh pieces
should be worked into the net by the manufacturer. One of these samples should be removed andtested at least annually to confirm the continued strength of the netting.

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The netting cord must be strong enough so that it does not break under the impact of the hammer,
abrade where it is attached or deteriorate unduly under the effects of ultraviolet ray exposure.
The cage must be properly operated during training and competition.

6.3.2.2 Hammer Cage (Figure 2.4.2.2)
The Hammer cage shall be designed, manufactured and maintained so as to be capable of stopping a
7.26kg hammer moving at up to speeds of 32m per second. This equates to a kinetic energy of 3.72kJ.
It may be assumed that Type B1 netting with a minimum breaking energy at end of life of 4.4kJ as
defined in EN 1263-1 will meet this requirement.
The netting which may be of suitable natural or synthetic fibre cord or of mild or high tensile steel wire
should be arranged so that there is no danger of the hammer ricocheting, rebounding or forcing its way
through joints in the netting or panelling, or under the netting.
The minimum height of the netting at its lowest point shall be 7.00m at the rear of the cage and at least
10m for the last 2.80m panels to the gate netting pivot points. There must be adequate attachmentsof the netting at ground level and at the top, which maintains the net in correct relationship to thethrowing circle under windy conditions.
The maximum mesh size for wire netting shall be 0.05m and, for cord netting, 0.045m and the minimum
breaking strength of cord or wire shall be 300kg. Alternatively, the energy absorption of the mesh shallmeet the dynamic test principles laid down in EN 1263-1 such that the netting will withstand an object
100kg mass being dropped into the netting from a height of 7m.
The netting may be in sections or in continuous form hung from a well-supported and braced framework.
It is desirable that the netting can be raised and lowered quickly. In any construction the minimum
distance from the centre of the circle to any point on the cage netting shall be 3.50m. The netting shallbe hung at least 0.60m clear of the support posts or frame so that a thrown implement cannot strike
the posts or frame when the netting moves under the impact. The netting should be of sufficient lengthand arranged so that when a gate is closed the netting is not moved closer to a supporting post. The
netting will need to have ropes threaded through it from each post cantilever arm to ground anchorsso as to minimise movement of the netting under wind and implement impact and be arranged as for atent guy so that the rope can be tensioned.
The supporting structure shall be rigid enough so that it does not deflect out of position unduly under
the weight of the netting or the force of the wind.
The width of the cage at the mouth should be 6.00m when measured to the insides of the netting
positioned 7.0m in front of the centre of the Hammer circle for the entire height of the opening. Two
movable netting panels 2.00m wide and at least 10.00m high shall be provided at the front of the cage.
These panels shall be constructed and erected so as to allow the panels to be opened and closed tosuit "right-handed" and "left-handed" throwers. The structures supporting the front panels (gates) shallbe easy to open and close manually and constructed so that they can be secured firmly in the fully open
and closed positions.

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The heights shall be measured to the lowest point of any netting catenary.
This cage is suitable for Discus Throw.
The Technical Rules indicates that for concentric circles in discus throwing configuration the Hammer
cage gates should be fixed parallel to the closer landing sector line. This will reduce the danger zone toapproximately 62° without impeding a throw. However, there is the opportunity for the danger zone to
be further reduced by moving a gate closer to the sector line without impeding a throw. The national
federation should advise where they want the gates to be positioned for discus throwing.
A cage that has a World Athletics Product certificate does not ensure that it meets the Technical Rules
unless it is installed exactly as shown in installation drawings and instructions, is operated andmaintained correctly.

6.3.2.3 Discus Cage (Figure 2.4.1.2)
The cage should be designed, manufactured and maintained so as to be capable of stopping a 2kg
discus moving at speeds of up to 25.00m per second. This equates to a kinetic energy of 0.63kJ.
The netting which may be of suitable natural or synthetic fibre cord or of mild or high tensile steel wire
should be arranged so that there is no danger of the discus ricocheting or rebounding or forcing its way
through joints in the netting. It shall be at least 4.00m high at the rear of the cage but rising to at least
6m for the last 3m to the mouth. The heights shall be measured to the lowest point of any netting
catenary. The end of the cage side particularly adjoining the track may be of greater height and/or
length to the minimum dimensions specified so as to prevent a wayward discus landing on the track or
beyond during a Discus Throw competition by going over the netting or past the end of the netting.
The maximum mesh size for wire netting shall be 0.050m, and, for cord netting, 0.045m. The minimum
breaking strength of the cord or wire at any time shall be 40kg. Alternatively, the energy absorption of
the mesh shall meet the dynamic test principles laid down in EN 1263-1 such that the netting willwithstand an object 15kg mass being dropped into the netting from a height of 7.00m.
The netting may be in sections or in continuous form hung from a well-supported and braced framework.
It is desirable that the netting can be raised and lowered quickly. In any construction the minimum
distance from the centre of the circle to any point on the cage shall be 3.00m. The netting shall be hungat least 0.60m clear of the support posts or structure so that a thrown implement cannot strike these.
The netting will need to have ropes threaded through it from each post cantilever arm to groundanchors so as to minimise movement of the netting under wind and implement impact and be arranged
like a tent guy rope so that the rope can be tensioned.
The supporting structure shall be rigid enough so that it does not deflect out of position unduly under
the weight of the netting or the force of the wind.
The width of the cage at the mouth, measured to the inner edges of the cage netting, should be 6.00m
positioned 7.00m in front of the centre of the Discus circle.

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This cage is not suitable for Hammer Throw.
A cage that has a World Athletics Product certificate does not ensure that it meets the Technical Rules
unless it is installed exactly as shown in installation drawings and instructions and is operated andmaintained correctly.

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TECHNICAL GUIDELINES
THROWING SAFETY CAGES STRUCTURAL DESIGN GUIDELINES
Introduction
These guidelines are provided for the information of the safety cage manufacturers and theirprofessional structural engineers.
It is expected that the cages including their footings or counterweights, in the case of free-standing
cages, will be designed in accordance with applicable national or international standards and theseguidelines. The number of the standards and the clauses used shall be quoted against the parts of thecalculation.
Free-standing cages and cages, the posts of which can be readily removed, may be regarded as
temporary structures.
As the cages will be installed in a variety of locations the worst exposure and the poorest groundconditions situations shall be assumed.
The cage design wind to be stated in the manufacturer’s documentation is assumed to be measured bya wind gauge with the anemometer positioned 1.2m above the ground level parallel to the direction of
the wind being experienced at the time.
All documentation should indicate that the cage is to be installed on level ground. This must be
particularly emphasised for free-standing cages.
Design Criteria
The designer will determine the loads likely to be experienced by the cage in accordance withappropriate national or international codes which shall be quoted. The most significant load for a cageis wind loading. The manufacturer may nominate a maximum wind velocity (measured as indicated above
when the netting must be completely lowered) or the designer shall assume the maximum exposure
situation.
The designer shall determine the worst wind direction situation for the cage which is likely to be one
perpendicular to the face of the netting on one side of the cage where the weight of the netting
marginally increases the overturning moment on a post caused by the wind.
Please note that throwing cages used at international competitions requiring Construction Category I,
II or III as defined in the Track and Field Facilities Manual Chapter 1 must be designed for a wind 15 m/s
or greater.
Wind Loading
Wind force F = c × q × A, where c = form factor, A = area(s) on which the wind is acting, q = windpressure = 0.5ρ × v2, where v = design wind velocity, ρ = air viscosity.
The form factor c may be determined from the appropriate code taking into account the positive andnegative pressures on the element.

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The area of netting exposed to the wind depends on its porosity factor i. For example, a 45 x 45 x 5mm
cord diameter net will have a porosity factor i = (452 – 402)/452 = 0.21
The overturning moment at the base of the post for the wind load and dead load might be simply
calculated as shown on the attachment.
Any computer programme used in the calculations should be identified and the input loads clearly
indicated. In most designs, it is not necessary to use a computer programme to the loads carried byeach post and its footing.
Footing Design
The footings shall be designed for the design wind load resulting bending moments plus dead load
vertical and horizontal reactions such that the soil bearing pressures are not exceeded for the poorest
assumed ground conditions at least sandy clay. Alternatively, a range of ground conditions may be
assumed and different footing sizes provided for each ground condition.
The footings design shall be based on established soil mechanics practice.
The footings may be simple mass concrete blocks, reinforced spread footings or concrete piles. In many
situations, bored piles may be the cheapest solution.
Throwing cage posts loads are similar to those carried by sign posts, lamp posts and flagpoles, as thegreatest horizontal load and bending moment is that caused by wind on the netting and the post. The
largest vertical load on the foundation is that from the weight of the footing.
Under wind loading, the post and the footing can be allowed to move enough that a lateral passive soil
reaction is applied to the side of the concrete footing (as the footing pivots slightly, passive soilpressure on opposing sides of the footing resists the movement).
The passive soil reaction at depth y = u × y × d × Kp, where y = depth of the footing, u = unit weightof soil, d = diameter (or breadth if it is rectangular) of the footing, Kp = coefficient of soil passive
pressure. Kp = (1 + sin ϕ) / (1 - sin ϕ), where ϕ = soil internal angle of friction.
The allowable soil pressure under the base of the footing is a higher value than the allowable lateralpressure.
There are a number of theories as to how the soil reacts to the horizontal force and moment applied to
the footing. For simplicity, it is sometimes assumed in US practice for masts and posts that the post
footing pivots at 1/3rd the depth of the footing above the base of the footing with the maximum soil
passive pressure on the upper part of the footing S1 = 0.33 × S3, where S3 is the allowable maximum
soil passive pressure at the bottom of footing. This is illustrated in the figure below.
If empirical data is relied upon in determining the size of the footings, the source documents shall bequoted.

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provide:

Fully dimensioned drawings of the cage and its footings which show inter alia the set-out; theoverhang dimension of the netting from the posts, post material and dimension, the size of thefootings, concrete quality and reinforcement;Wind load and structural calculations (by a professional structural engineer, in English) for the
structure and its footings for various soil conditions to prove that the posts have adequate strengthand there is a minimum factor of safety of 2 against overturning for footings in the ground and of 4
for free-standing cages relying on counterweights for stability at the design wind speed;

Detailed instructions for setting out and installing the footings, gate fixing anchors (hammer cage),cage structure and the netting;

Detailed instructions for gate operation and anchoring (hammer cage), and netting tensioning andanchoring;Throwing Cages - December 2020

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Details of the netting dimensions, strength and the specifications.



The installation, operation and maintenance instructions and all documentation should be mandatory
in English

Detailed instructions for the periodic safety inspections of the cage and its fittings.

Once World Athletics is satisfied with this detail then a World Athletics inspector will examine an
example of the cage at the manufacturer’s expense using the proforma inspection report to check theadequacy of the cage and its ease of operation. The inspector may recommend improvements to thecage.

All existing cage designs should also be reassessed against the updated design criteria in the revised
Manual particularly the minimum clearance of netting from posts. All the manufacturers should post on
their websites the safe design wind speed for each of their certified cages.

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TECHNICAL GUIDELINESADVICE TO TECHNICAL OFFICIALS AND FACILITY OWNERS
Existing Cages
Many of the older cages were not designed for the netting to remain in place after the completion of acompetition or a training session.
World Athletics, since requiring more information from manufacturers seeking a Product Certificate for
their cage, has found that some cages in fact have quite low design wind speeds. World Athletics has
now determined that cages that are to be used for major international competitions shall have a design
wind speed of 15m/s or greater.
The minimum design gust wind speed for permanent structures designed by ultimate limit state analysis
is according to the local regulations.
It is therefore suggested that there should be appropriate instructions promulgated at each venue when
the cage netting must be lowered so as to protect the investment.
New Cages
Before purchasing a new cage, determine how you want to operate and maintain the cage.
The selection of cage type will also depend upon:

Security of site

Accessibility of public/unsupervised usersHow cage and netting is to be maintained

Potential for damage e.g.; fire risk (nearness of vegetation), vandalism, misuse by users

Use of chain wire instead of cord netting could be a considered as an alternative particularly for training
venues.
Hammer cages with metal framed gates are not recommended as the gates and their netting are very
prone to damage from hammers, the gates are often very difficult to move particularly in a strong wind
and if not locked firmly in the open or closed position can swing around and demolish a cage.
There are some designs with hung netting gates or sliding netting gates available.
Can the cage structure stay in place permanently? If not, how will the cage structure be installed or
removed quickly without heavy lifting equipment?
The posts and anchor points can either be installed in sockets set into the post footings or attached toa fixed or hinged baseplate set into the footing. The latter may be the better solution.

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If a cage structure can remain in place, then a cage with posts permanently set into the footings would
be acceptable. However, note that the posts are longer and heavier, and accurately placing them plus
keeping them vertical during footing concreting may be difficult.
Determine the make(s) of cage which meet your operational requirements with the design wind speed
which meets your requirements and select the appropriate-sized footing for the soil conditions existingat your site.
If possible, have the cage supplier also install the required footings.

This document is for guidance and information purposes only and any drawing within is also for
illustration purposes only. This guide is not a specification and must not be regarded as so. Any person
who places reliance on it does so at their own risk who are responsible for satisfying themselves of its
reliability. Manufacturers who use these guidelines to design and manufacturer their own [cages] areresponsible for constructing, testing their products in compliance with all applicable laws and inaccordance with any health & safety laws and regulations. To the fullest extent permitted by law, World
Athletics does not accept any liability for any errors or omissions contained in this guidance, defects inthe design or manufacture of cages by any third party as a result of using this guide or breach of any
health & safety laws or regulations.

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