Here are three accounts of the sparks that were seen coming out of the ship.
Harold Bride
"Smoke and sparks were rushing out of her funnel. There must have been an explosion, but we heard none. We only saw the big stream of sparks."
Charlotte Collyer - Her account was printed in newspapers, and it is uncertain if the editor added his own touch to make it sound more dramatic.
"It came with a deafening roar that stunned me. Something in the very bowels of the Titanic exploded and millions of sparks shot up to the sky, like rockets in a park on the night of a summer holiday. This red spurt was fan shaped as it went up, but the sparks descended in every direction in the shape of a fountain of fire. Two other explosions followed, dull and heavy, as if below the surface. The Titanic broke in two before my eyes."
Jack Thayer
"One of the funnels seemed to be lifted off and fell towards me about 15 yards away, with a mass of sparks and steam coming out of it. I saw the ship in a sort of a red glare, and it seemed to me that she broke in two just in front of the third funnel." In another account he said, "The second funnel, seemed to be lifted off, emitting a cloud of sparks. It looked as if it would fall on top of me. It missed me by only twenty or thirty feet."
Neither Jack or Harold apparently heard the explosion, but those further away did hear it. I have read that survivors from bomb attacks described how they never heard the actual blast when it exploded just feet away from them. e.g. A survivor of the 7/7 London bombings said - "I did not hear a loud bang. Actually, it was almost the total opposite, like all sound shut down, as if I was deeply, deeply, deeply underwater, so the hearing was all muffled. It was all like distorted sounds, but of a very low tone."
Fred Barrett said - "When the ship was sinking a volume of smoke came up."
Philip Mock said - "After the noise I saw a huge column of black smoke slightly lighter than the sky rising high into the sky and then flattening out at the top like a mushroom."
Frank Osman said - "After she got to a certain angle she exploded, broke in halves"
He was asked.
Q - What do you think those explosions were?
A - The boilers bursting.
Q - What makes you think that?
A - The cold water coming under the red-hot boilers caused the explosions.
Q - You reasoned that out?
A - Yes; but you could see the explosions by the smoke coming right up the funnels.
Q - Did you see any steam and smoke coming?
A - Yes.
Q - Did you see any sparks?
A - It was all black; looked like as if it was lumps of coal, and all that.
Q - Coming up through the funnels?
A - Through the funnels.
Q - That is, there was a great amount of black smoke coming up through the funnels just after this explosion?
A - Just after the explosion.
Q - And there were lumps of coal, etc, coming up?
A - Yes; pretty big lumps. I do not know what it was.
Q - Did any water come up?
A - I never seen no water; only the steam and very black smoke.
Depending on where each person was, they would undoubtedly witness different events that were occurring at the same time. The stern appeared to keel over and turn around after she broke, so this would conceal some events aboard and expose others, depending on where each witness was at the time.
It is possible that the sparks were caused by the separation of electric cables as the ship broke in two. This effect times several hundred perhaps. e.g.
.