Recently problems of smoke from fires have been of growing concern. The irritative effect of smoke is one of the problems. Acrolein and formaldehyde are considered two of the most irritative materials among combustion products of organic materials which consist only of carbon, hydrogen and oxygen. The present study concerns the extent of these products evolved from combustion and pyrolysis of synthetic and natual polymers. The evolution of acrolein was the highest at 350-450 °C (below the flaming temperature) while air was supplied to the electric cylindrical furnace. However, when nitrogen gas was supplied, while heating oxygen-containing materials, maximum evolution of acrolein occurred at 600 °C.
The materials which evolved the maximum amount of acrolein, 0.5-3.5 mol per gram of material, when heated at optimum temperature, were in the order: polyethylene, polypropylene, vinylon and cellulose. The amount of acrolein is only one tenth of the amount of formaldehyde evolved, but the toxicity of acrolein is only one tenth of the amount of formaldehyde evolved, but the toxicity of acrolein is tewnty times greater than formaldehyde. Therefore, the evolution of acrolein can be said to be more dangerous than that of formaldehyde.
For materials containing no oxygen, it is considered that oxygen atoms are supplied from the atmosphere. However, in the case of cellulosic materials it is indicated that most of the oxygen atoms contained in acrolein molecules comes from cellulosic materials themselves.
Only materials which would continue to smolder in the normal atmosphere were subjected to the smoldering experiments under more practical conditions, where specimen was kept contact with a heated nickrome wire, in order to determine the evolution of acrolein and formaldehyde.
The experiment results showed that the amounts of both acrolein and formaldehyde from cellulosic materials were 1/2-1/3 of the greatest amount obtained from the furnace experiments. The figures are still not too small and considered to be at a dangerous level.
In order to know the theoretical extent of which the toxic level in an average size room increases with time, the concentrations of acrolein and formaldehyde in a 25 m³ room versus time were calculated from the smoldering rate of cotton batting and the ventilation rate of the room (1 air change per hour). It was found that a considerably hazardous condition could be reached even before flaming occurs.

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An experimental study has been conducted to explore the effect of thickness on downward flame spread over thin solid-fuel sheets in an upward air stream. Flame spread rates over paper of four different thicknesses at various air-stream velocities were measured, and the gas velocity and temperature profiles in the vicinity of spreading flames were examined using particle tracer techniques and fine-wire thermocouples.
It was confirmed that the spread rate of a stably spreading flame decreased with the increase of the thickness. The gas velocity profile in the vicinity of the leading edge of the preheat zone and the gas temperature profile in the preheat zone were almost independent of the paper thickness. In the case of stable flame spread, the mass burning rate decreased with the increase of the air-stream velocity and increased with the increase of the thickness. The increase of the mass burning rate with the paper thickness was confirmed to be partly due to the heat transfer to the unburned material through solid phase, and mainly due to the existence of the solid-phase temperature difference in the direction normal to the paper surface.

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In the Report 1, the push-pull type air shutter is suggested as a new type equipment for fire protection, and it is mentioned that the one has a possibility to be effective and well-directed both on protection from fire and smoke and on escape, and in addition the design method is referred to.
The method is described in the preceding paper on an assumption that the shutter ought to have an enough capacity to shut smoke and toxic gases perfectly, but from different point of view, in the purpose of reducing the initial and running costs of equipment, permitting a little smoke and gases to leak through the air shutter, it is naturally considered that the exhaust flow rate of the air shutter can be decreased. Nevertheless, as the escapers in safety zone in the case should be kept their securities, naturally the limit of the exhaust flow rate to be reduced should exist.
Then this time, in order to determine the limit values the air shutter model on the scale of 1/60 is applied.
By the way, the equation to determine the volume rate of pull flow Q₃ on push-pull type air shutter is given as follow¹⁾:
Q₃ = Q₁(1+m · K_B ) …………………………(1)
where, Q₁ is volume rate of push flow, m break safety factor and K_B the break limit flow ratio which is determined by the shape ratio of air shutter and the side flow velocity ratio V₀/V₁. Now, in the experiment the upper equation (1) is reformed dimensionless as follow:
Q₃/Q₁ = 1+m · K_B …………………………(2)
Then, the experiment is run varying the push-pull flow ratio Q₃/Q₁ and the side flow velocity ratio υ₀/υ₁ to research “smoke leak ratio” and we get following results.
(1) As the aims of push-pull type air shutter for fire protection are primary to secure the escapers from smoke and gases at earlier stage of fire breaking out and secondly to prevent and exhaust smoke and fire extending, and tertiary to make fire fighting easy, in the design the value of the smoke leak ratio ought to be zero, and it means the value of m in the equation (1) has to be appointed larger than 1.
(2) When the value of m is appointed smaller than 1, and interception of shutter is imperfect, even if the value of smoke leak ratio is small, the permissible time to refuge safety is very short, and once the smoke begins to leak toward the safety zone, immediately the smoke concentration in the zone rises up and it brings bad visibility which makes unable to escape.
1) T. Hayashi et al.; Characteristics of Push-pull Hoods and Design Method of the Ones (1)-(5), Bulls. of Presentations of the Society of Heating, Air-Conditions and Sanitary Engineers of Japan, 1970-1974.

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