Flash Fire Protection

Flash fire is a significant hazard across many industries, predominantly the oil and gas industry, and manufacturing industries where combustible dust is produced.

It’s vital to perform extensive risk assessments to reduce the risk of flash fire, but other measures can be put in place to protect individuals where hazards are present. This includes providing sufficient PPE for operatives where a risk is identified. Keep reading to find out more about how flash and arc fires occur, and what can be done to protect against thermal injury.

What is a flash fire?

A flash fire is a fire is a sudden fire characterised by extreme temperature (can reach an excess of 800° C) and a rapidly moving flame front. It is caused by ignition of a mixture of air and a diffuse fuel (flammable substance), such as:

• Gas
• Dust
• Vapour (e.g., an aerosol)

This occurs without the production of damaging pressure when a source of fuel is ignited. For example, a spark generated by machinery igniting gas released from a damaged gas main would result in a flash fire.

Only a few seconds can make the difference between life and death, and a flash fire will usually last until the fuel is exhausted (i.e., the combustible substance is removed), therefore, it’s vital that PPE is worn to protect the wearer whilst potentially being engulfed in flame until they can either move away from the flame, or the flame is extinguished.

How do you protect against flash fire?

Effective risk assessments should be carried out to minimise or remove the risk of flash fire, where possible. In industries such as gas distribution, flash fire may not be able to be avoided altogether due to the nature of the service, so it’s crucial for adequate protective equipment and clothing to be provided to operatives working alongside gas.

During a flash fire, an individual may be engulfed in flame, facing extreme heat in a very short time. Burns occur when too much heat energy encounters the skin from a heat source. Skin cells can often handle a slow rise in heat but, if the skin absorbs too much heat too quickly, the cells will break down and die (i.e., resulting in serious burns). Flame resistant (FR) clothing is essential for preventing or slowing the transfer of heat from the flash fire flames to the wearer’s skin to prevent burns. It’s important that the garments worn are fit for purpose and intact, as damaged FR clothing will not protect the wearer sufficiently.

What FR clothing standards should I look for?

All FR clothing will be tested to different safety standards to determine the level of protection and suitable application. There are two standards you should look for when choosing your flash fire protective wear:

EN ISO 11612: Clothing to Protect Against Heat & Flame

EN ISO 11612 applies to a range of applications, including protection against hazards including convective heat, radiant heat, contact transfer, and splatters of molten metal and aluminium.

This standard consists of five different heat transfer resistance tests, assessing the resistance of the fabric to the hazards above. The results of the tests are denoted by the letters A, B, C, D, E and F, paired with a number to indicate the performance level of the fabric within the test.

To adhere to this standard, the material must not ignite or melt at a temperature of 180°C and must not shrink by more than 5%.

The following tests can be carried out as part of EN ISO 11612:

• ISO 15025 (Letter A)
  • Procedure A (Surface Ignition, Class A1)
  • Procedure B (Edge Ignition, Class A2)
    
    
• ISO 9151 (Letter B) – Convective Heat (heat transmission through flame)
  • Fabric withstands 4-10 seconds (Class B1)
  • Fabric withstands 10-20 seconds (Class B2)
  • Fabric withstands 21 seconds or longer (Class B3)
    
    
• ISO 9642 (Letter C) – Radiant Heat (heat transmission through infrared rays)
  • Fabric withstands 7- 20 seconds (Class C1)
  • Fabric withstands 20-50 seconds (Class C2)
  • Fabric withstands 50-95 seconds (Class C3)
  • Fabric withstands 95 seconds or longer (Class C4)
    
    
• ISO 9185 (Letter D & E) – Molten Metal Splatters
  • Molten aluminium classification:
    • Fabric withstands 100-200 grams of molten aluminium (Class D1)
    • Fabric withstands 200-350 grams of molten aluminium (Class D2)
    • Fabric withstands 350 grams or more of molten aluminium (Class D3)
  • Molten iron classification:
    • Fabric withstands 60-120 grams of molten iron (E1)
    • Fabric withstands 120-200 grams of molten iron (E2)
    • Fabric withstands 200 grams or more of molten iron (E3)
      
      
  • ISO 12127 (Letter F) – Contact Heat
    • Fabric withstands 5-10 seconds (Class F1)
    • Fabric withstands 10-15 seconds (Class F2)
    • Fabric withstands 15 seconds or longer (Class F3)

BS ISO 13506: ‘Flash Fire’ Test for Protective Clothing Ensembles

The BS ISO 13506 Protective Clothing Against Heat and Flame standard tests complete garments to determine burn injury using an instrumented manikin. Within the test, a set duration of flash fire will engulf the manikin, with a calculation being made after the test to predict the level of pain, as well as any 1^st, 2^nd, or 3^rd degree burns the wearer would have received while wearing the garment during the event of a flash fire.

This standard is purely a test for flash fire, with no specified parameters for performance, as this is not a performance standard. The test sets no pass/fail criteria but allows garments to be tested as per a company’s individual safety standards as set within a risk assessment carried out by their Health & Safety Officer. Customisable criteria within this test may be the duration of the flash fire, as well as whether any under-layer is present.

ISO 13506 ensures that a garment ensemble is able to provide adequate protection in the context determined by the risk assessment, meaning it can be tailored to the individual organisation’s needs.