Summary of the requirements and procedures under the PAS68 and ASTM standards.

This document is produced to give a synopsis of impact testing of vehicle security barriers and to explain why these words – impact tested – that appear in our specification sheets are so relevant to product choice.

Historically most producers of fences, gates and other equipment have included in their product description the word “security”.   This word – security - has no relevance unless compared to a standard.

In this paper the reference to vehicle barriers, refers to static and rising bollards, deep and shallow foundation road blockers, vertically rising beams, hinged rising beams, and swing or sliding gates.  The ultimate threat to high security sites is a forcible attack with vehicles carrying high explosives.   These are referred to as VBIEDs (vehicle borne improvised explosive devices). 

As the term VBIED indicates, these devices could be carried on a variety of different mass vehicle types, travelling at various speeds.   To ensure users can select or be advised on the correct product, it is now required by many Country governments and corporate bodies that vehicle barriers be physically tested prior to being selected and installed.   This is undertaken by independent test laboratories where a full size vehicle is propelled into the barrier under test.

There are various International standards for VSBs (vehicle security barriers).   The most widely used and respected are the United Kingdom’s British Standard Institute (BSI) publicly available specification (British PAS) 68 and the United States’ ASTM F2656-07.   Shortly there will be a European CEN workshop agreement (CWA) that will use the PAS 68 (impact test standard) and PAS 69 (site survey and installation procedures) as source texts.   It is envisaged that the PAS 68 standard will be the most appropriate for Eastern Europe and CIS countries.

The traditional test vehicle in US testing has been the 15000 lb truck (6.8 tonnes) and the UK has done the majority of testing with a 7.5 tonne truck.   The US vehicles differ in many dimensional and structural respects to those of the European and Japanese makers and there are differences in impact test results on certain products.  Because of this, those selecting vehicle security barriers need to assess their environment and select the most appropriate standard, or choose a barrier that has been successfully tested to both the PAS 68 and ASTM tests. 

Both test standards have certain common impact speed, vis

30 mph (48 km/h), 40 mph (64 km/h) and 50 mph (80 km/h)

The BSI PAS 68 standard also includes 10 mph (16 km/h) and 20 mph (32 km/h) and a range of other vehicle types such as a 1.5 tonne car, 2.5 tonne 4x4 pickup, a 3.5 tonne van or a 30 tonne 4-axle rigid truck.

 The PAS 68 standard defines the vehicle type, penetration (this is the distance travelled by the leading edge of the load carrying area beyond the VSB after impact), dispersion (this is the distance that any major debris is thrown beyond the VSB during the test) and records the angle of vehicle approach.   For example a fixed bollard impacted by a 3.5 tonne (3500kg)  van in a Vehicle Impact Test travelling at 30mph (48 km/h) and with a 90 degree impact resulting in a vehicle penetration of 1.7m and dispersion of 5.2m will be expressed as follows:- Fixed Bollard V  3500 / 48 / 90 : 1.7 / 5.2

It is not a requirement of the test that the vehicle security barrier should be re-useable after the impact but if they were usable, this is made as an observation. This may be considered a very important factor to specify if the protected property only has one entrance.
The US standards are being re-classified under the ASTM rating. However, this has historically been expressed as the K factor

K4 15000lb vehicle travelling at 30 mph
K8 15000lb vehicle travelling at 40 mph
K12 15000lb vehicle travelling at 50 mph

High security areas over which government has control increasingly use a defined impact rating to suit their purposes. This relates to the risk assessment and the budget allowances. This is usually defined by each individual ministry.

It is also worth noting the following additional points. If a vehicle security barrier has been tested by say a car travelling at a high speed then the vehicle barrier will not necessarily perform in the same way when impacted by a heavier vehicle travelling at a lower speed even if the kinetic energy of the two impacts is approximately the same. Also, it should be noted that the foundations, fixings and below ground reinforcement used for the test are considered an integral part of the product. Therefore, any recommendations will include the type of foundation required and this may need to be adapted for the soil conditions found on site.

Ultimate users can calculate what kinetic energy will be generated as long as they know the probable gross weight of the attacking vehicle and can assess the probable highest approach speed by using the following formula:

Kinetic Energy J = mass x speed²
                            2

Therefore, for a vehicle weighing 7.5t travelling at 50mph (80km/hr) prior to impact has the following value of kinetic energy:

Mass in tonnes
Speed in m/second

7.5 x (80 x 1000 / 3600)²
2
= 1,851

Latest developments in impact testing include the Introduction of Pass 170-1 bollards-non-vehicle low energy impact testing using linear impact test method and PASS 17—2 using pendulum test method. Also the PASS 68 has been adopted as the basis for European standard CWA 16221 which is now issued. This in turn will lead to the integration of the ASTM and EU standards into a world standard under the auspices of ISO.

It is recommended that potential users of vehicle barriers for prevention against forcible attack visit the CPNI website www.cpni.gov.uk

This illustrates the relationship between the speed of the attacking vehicle to the impact load and highlights the need to reduce the approach speed as much as possible.

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