Explosion from iron powder

Am explosion occurred when adding iron powder to an EDTA solution at 60 C in a chemical reactor (EDTA = Ethylene-diamine-tetra-acetic acid ).
Hydrogen was produced by a chemical reaction and ignited by static energy, probably due to the fact that the iron powder was coming from non-conducting polypropylene container (IBC = Intermediate Bulk Container).
Two workers were injured.

INITIATING CAUSE:
the addition of iron to the EDTA solution triggered an unwanted dissociation producing hydrogen.

ROOT CAUSE
This is a case where the hazards were known, but the risk assessment was not properly done.

chemical reactor

DESCRIPTION OF THE PROCESS
Ethylene-diamine-tetra-acetic acid (EDTA) is a chelating agent which can bind metals.
EDTA is used to solubilize iron(III) in water. In the absence of EDTA or similar chelating agents, ferric ions form insoluble solids and are thus not bioavailable.
It is used for example in the paper industry, to bleach pulp, and in agriculture, to treat diseases.

2 persons injured, one of which hospitalised for less than one week.

The company was found breaching the Health and Safety at Work Act of 1974, specifically Section 2(1): "It shall be the duty of every employer to ensure, so far as is reasonably practicable, the health, safety and welfare at work of all his employees."
The hazards related to hydrogen, explosive dust and ignition had all been recognised earlier by Company, but an inadequate risk assessment had been performed.
Nevertheless, it was considered that mitigation outweighs reasons for Prosecution

This is a case where the hazards were known, but the risk assessment was not properly done.

(1) To reduce liquid temperature and therefore the evolution of hydrogen; to feed 25 kg bags via earthed, worm-feed/hopper unit.

(2) To use 2 reactors - one for making up warm starter solution and one for pre-mixing iron powder.

(3) to increase and modify nitrogen feed, from the sparge ring at reactor base, to directly to top of liquid.