Montgomery Counties Needham Fire HAZMAT has been dispatched to assist firefighters in Bellville, Texas after an early morning explosion at the Western International Gas Plant there. In addition to the locals Harris County HAZMAT has also dispatched their units. The plant which bottles acetylene also supplies oxygen, breathing air, helium, hydrogen, carbon dioxide, nitrogen and argon. which reported the first explosion just after 6:30am. Since that time there have been many additional explosions. Residents were initially evacuated up to a mile away. That area is now back to 5-miles. In addition firefighters have evacuated the facility. One of the major concerns is a hydrogen tank which could explode. Hydrogen is lighter than air and diffuses rapidly — 3.8 times faster than natural gas — which means that when released, it dilutes quickly into a nonflammable concentration.Hydrogen rises two times faster than helium and six times faster than natural gas at a speed of almost 45 mph (65.6 feet/second). Therefore, unless a roof, a poorly ventilated room, or some other structure contains the rising gas, the laws of physics prevent hydrogen from lingering near a leak (or near people using hydrogen-filled equipment). Simply stated, to become a fire hazard, hydrogen must first be confined; however, because hydrogen is the lightest element in the universe, it is very difficult to confine. Industry takes these properties into account when designing structures in which hydrogen will be used. The designs help hydrogen escape up and away from the user in case of an unexpected release. Hydrogen combustion primarily produces heat and water. Due to the absence of carbon and the presence of heat-absorbing water vapor created when hydrogen burns, a hydrogen fire has significantly less radiant heat compared with a hydrocarbon fire. Because a hydrogen fire emits low levels of heat near the flame (the flame itself is just as hot), the risk of secondary fires is lower. An explosion cannot occur in a tank or any contained location that contains only hydrogen. An oxidizer such as oxygen must be present in a concentration of at least 10% pure oxygen or 41% air. Hydrogen can be explosive at concentrations of 18.3% to 59%. Although this range is wide, it is important to remember that gasoline can present a greater danger than hydrogen because the potential for explosion occurs with gasoline at much lower concentrations: 1.1% to 3.3%. Furthermore, there is very little likelihood that hydrogen will explode in open air due to its tendency to rise quickly. This is the opposite of what we find for heavier gases such as propane or gasoline fumes, which hover near the ground, creating a greater danger for explosion.