Bomb Suit Survivability Explained: The importance of blast trials and critical performance testing

Counter-IED Report Winter 2021/2022

By Joe English, Lead EOD Engineer and Product Manager for NP Aerospace and Siti Pareti, formerly Counter-Explosive Ordnance Adviser, UK Defence and Security Exports, Department for International Trade

Blast trials are a critical part of Bomb Disposal Suit Development. They are required by public safety standards such as the National Institute of Justice NIJ 0117.01 and are designed to ensure the suit’s ability to reduce the blast and fragmentation hazard. The collection of critical data on the blast’s effects on the body allows manufacturers and the wider industry to ensure that bomb disposal suits protect operators from long term damage and increase survivability. This data includes blast overpressure which is particularly damaging to the lungs and ears, and blast induced head injury. Bomb disposal suits are the last line of defence against blast and fragmentation therefore the operator’s ability to conduct EOD tasks whilst in the suit must not be impeded. Visibility and movement can be significantly improved via suit design but also accessories such as cooling and communication systems.

Impact of Blast
Blast is a complex product of the detonation of an explosive device and its effects can be categorised into four groups. Primary blast refers to the effects of a rapid increase in pressure, particularly affecting body organs containing air, i.e. ears, lungs and gastrointestinal tract. Whilst primary blast can cause fatalities, there is also significant risk of debilitating physical injuries such as Blast Lung and also mental injuries. Secondary blast refers to fragmentation, both primary and secondary. Tertiary blast refers to the effects of the blast wind which results in displacement of the body as well as possible traumatic amputation. Quaternary blast refers to the effects of the heat and flame of the fireball. Manufacturers need to take into account all of these aspects and undertake rigorous and extensive testing. NIJ 0117.01 specifies a single blast trial 0.567kg C4 @0.6m kneeling. However, some manufacturers go beyond this. NP Aerospace tests against 4 scenarios: 0.567kg C4 @0.6m kneeling, 1kg PE4 @1m standing, 2kg PE4 @2m standing and 10kg PE4 @3m standing as each can affect the body differently.

Survivability and the Bowen Curve
In order to standardise and compare testing, manufacturers use different methods of measuring data. The most common being Blast Overpressure reduction, where pressure sensors are placed both inside the suit (typically at the lung and ear) and compared to external reference sensors to calculate the suit’s effectiveness against the harmful effects of peak pressure. Blast overpressure can be plotted on the Bowen Curve, which offers a measure of the probability of survivability due to lung injury for operators wearing EOD Suits. This was established in the titled paper ‘Estimate of man’s tolerance to the direct effects of air pressure’. The advantage of the Bowen Curve is that it provides qualitative data which suit
manufacturers can use as a starting point when conducting tests. In recent blast trials, our 4030 ELITE suit survivability rating exceeded 99% for all scenarios – significantly reducing the risk of lung injury.

Blast Trials
Live explosive Blast trials offer the best way to replicate as near to a real-life EOD or IEDD scenario as and much work has been done in this area. Anthropomorphic Test Devices (ATDs) or ‘crash test dummies’ have become more scientific and informative alongside improvements made in automotive testing. The Millbrook ATD used in the 4030 ELITE blast trials was a Hybrid III 50th percentile male dummy with 16 internal sensors (3 accelerometers located at each Head, Chest andPelvis, a 6-Axis Load Cell located at the Neck, and a deflection Displacement sensor located at the Chest) a further 4 external pressure sensors (located at each Left and Right Ear, Centre and Side Chest).

The ATDs are dressed in the EOD suit and set up in a kneeling or standing position facing the explosive – allowing to freely fall back when subjected to the force of the explosion. Different explosives are used according to the criteria being tested. In the case of the 4030 ELITE testing both C4 and PE4 plastic explosives were used. Blast testing is conducted at external laboratories or blast sites for large scale testing. In the case of the 4030 ELITE suit testing NP Aerospace used two test facilities, Oregon Ballistic Laboratories (OBL) in the US and Ordnance Test Solutions (OTS) and Phil Gotts Consulting in the UK.

Blast Trial Results
Blast trials for the 4030 ELITE suit were undertaken in the UK and US. The following data is for the four scenarios performed in the UK. In each scenario two suits were used, facing towards the centrally placed explosive charge at the required standoff distance. Using two suits allows an average result to be calculated, accounting for any non-uniform blast distribution. Following the detonation and once the range is made safe – the first thing the manufacturer does is fully inspect the suit, checking that all components remain locked and secure on the ATD – focusing on the Helmet Retention System, Face Shield, Plate Buckles, Zips and Quick Release System. The Suit and Helmet are then removed checking that all fastenings continue to operate. The Inside of the Suit and ATD are examined to check there is no sign of damage or penetration which could injure an operator. NP Aerospace uses a polyolefin coverall witness suit under the EOD Suit to identify any ingress of heat and flame. On completion of the trial all data gathered from the ATD is analysed to ensure the suit has performed correctly, reducing blast overpressure to prevent injury to lungs and mitigate head injury. NIJ 0117.01 does not include measuring the blast effects on the body, through either blast overpressure reduction, comparison with the Bowen Curve or chest wall acceleration. The 4030 ELITE Bomb Suit provides the following percentage reduction in blast overpressure at the chest and ear compared to external pressure in four scenarios.

Blast Scenario% Reduction in Blast Overpressure at Chest% Reduction in Blast Overpressure at Ear
0.567kg C4 @ 0.6m kneeling (NIJ 0117.01)99%99.7% to 99.8%
1kg PE4 @ 1m standing94.5% to 97.1%98.7% to 99.6%
2kg PE4 @ 2m standing86% to 93.2%97.3% to 98.0%
10kg PE4 @ 3m standing87.7% to 93.1%97.2% to 98.4%

Other Critical Performance Testing

Blast trials should not be carried out in isolation. There are other significant performance tests undertaken by the manufacturer such as fragmentation, flammability and ergonomics. You can read the full article and further testing here: from page 45.