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Testing of HDPE-manholes for fire hazard

Ministry of works - Bahrain

Introduction:

Manholes made of Polyethylene have been used successfully for more than 40 years Worldwide. It is a growing market and the advantages of manholes made of thermoplastic materials are well known:

  • No leakages
  • Easy handling
  • Low weight
  • Durability > 50 years
  • Impact resistance
  • Flexibility
  • High Strength
  • Tailor-made design for any load case
  • Easily Fabricated – important for future connections

In this case, the Ministry of Works – Bahrain had reservations concerning the possible flammability of the HDPE manholes during and after installation. These reservations had to be answered clearly and without any remaining doubt!

 

 

“Would the manhole burn if an ignited material was accidentally dropped into it?”
“Could the manhole be deliberately set on fire using common place equipment?”

 

Of course everyone is aware that Polyethylene is a plastic material and is flammable. It can be classified e.g. according DIN 4102-Part 1 into class B2, what is representative for “normal flammable materials”. That is not really surprising because it is a plastic material. Having said this, the manufacturers are using the temperature-behaviour of Polyethylene very successfully for their production processes.

 

“How would you rate the risk of ignition under defined conditions?”
“How could you demonstrate the varsity of the material under these conditions?”

 

The following described type-test, made in Bahrain 2014 for a local approval, show clearly that Polyethylene manholes have also under irregular usage no problems and fulfil all requirements!

 

Type testing for fire hazard and resistance

The test-procedure is developed for testing HDPE Manholes for fire hazard and resistance. The test should determine if HDPE manholes will catch fire and continue to burn under two different scenarios. These scenarios should emulate the possibility of either an accidental incident or intentionally attempting to set the manhole on fire. 

 

Specimen: 1400mm ID HDPE Manhole @ 1.8m DTI,
including benching to MOW (Ministry of Work) specifications.
Inlet and outlet are closed off via HDPE welding at the entry and exit points. 
Apparatus: Match Stick
Ignited Cigarette Lighter
Burning Cigarette
Burning Kerosene Block
Petrol

 

Scenario 1:

Manhole stored at site in a securely bounded area, standing vertically. 

Acceptable storage conditions necessitate these manholes to be kept in vertical position, with safe distance from each other, stored in a locked yard near site office guarded by security (As is standard on all MOW sites).

 

Other assumptions: Ambient temperature between 35˚C and 45˚C, with wind speed less than 15 km/h.

Following nuances are assumed to occur:

a.

Fire Test using Match Stick
Throwing of ignited match stick into the manhole.

Fire duration was under 5 seconds and extinguished itself out, leaving no damage to the manhole.

1 
b.

Fire Test using Ignited Cigarette Lighter:
Fire duration was under 5 seconds and extinguished itself out, leaving no damage to the manhole.

2
c.

Fire Test using Burning Cigarette:

Throwing of ignited cigarette into the manhole.
Fire duration was under 5 seconds and extinguished itself out, leaving no damage to the manhole.
3
d.

Fire Test using Burning Kerosene Block:

Placing of ignited Kerosene soaked block onto HDPE sheet.
Fire duration was under approximately 6 minutes and extinguished itself out, leaving no discernible damage to the HDPE sheet.

During Test DDuring

5

Conclusion of testing according scenario 1:

The HDPE Manhole was proved to be fire resistant under these conditions and it was observed that the fire failed to burn or sustain for long, thus causing little to no damage on the HDPE Manhole and sheet.

 

Scenario 2:

Simulation of Manhole installed with top and unlocked lid

Other assumptions:
Ambient temperature between 35˚C and 45˚C.
Manhole in full operating mode including some fluid in the flow channel.

Following nuances are assumed to occur in the case of the unlocked CI lid:

  1. Close and seal all upstream and downstream connections.
  2. Open lid.
  3. Put petrol (3-4 liters) inside manhole.
  4. Close lid in order to accommodate buildup of fumes for approx 5 minutes.
  5. Open lid.
  6. Throw in petrol soaked rag and ignite petrol.
  7. Close lid.
  8. Allow the petrol to burn out.

 

Fire Test using Burning Petrol;

Fire duration was approx. 30 seconds and extinguished itself out, leaving no damage to the HDPE Manhole.

Setting Up to MS RequirementsSetting Up to MS Requirements

Igniting the petrolIgniting the petrol
Fire Burns OutFire Burns Out Inside Manhole after Fire - No DamageInside Manhole after Fire - No Damage

 

Conclusion of test according scenario 2:

The HDPE Manhole proved to be fire resistant under the conditions as set up in the Method statement. It was observed that the fire burned out and did not ignite the HDPE material, thus causing little to no damage on the HDPE Manhole.

All tests are witnessed by:

  • Staff and QC, Krah Bahrain
  • Representatives from MOW, MED, SEPPD, SEOMD, RPMD and other departments, Kingdom of Bahrain
  • Representatives from Civil Defense, Kingdom of Bahrain

 

Author:

Claude Hendy
KRAH BAHRAIN CO. W.L.L.