Safety Engineering $-$ design criteria: safe design of a workplace $-$ collaborative activity

In a factory, there is a tank filled with gasoline. The tank has a maximum capacity of $2,500$ liters. The room housing the tank

is maintained at $15C$ and has dimensions of $65\mathrm{.}6168$ feet in length, $59\mathrm{.}05515$ feet in width, and $13\mathrm{.}1233$ feet in height. For

simplicity, assume the tank is the sole object in the room.

A worker is required to visually inspect the room six times daily, with each inspection lasting $10$ minutes. If the worker is

exposed to chemical concentrations exceeding the STEL level, medical care is needed, costing $$30,000,$ and the company

incurs a fine of $$150,000.$

The safety engineering team is assessing the unlikely scenario of a tank rupture occurring once every five years, leading to

the entire volume of gasoline spilling instantaneously onto the work area. For this scenario, the liquid gasoline is assumed

to uniformly cover the floor. The full floor area is taken as the evaporation surface. Under the same conditions, BuAc has an

evaporation rate of $0\mathrm{.}1$ liters $\frac{?}{m^{{?}^{{?}^{?}}}}\frac{2}{?}$ minute. Given that gasoline's evaporation rate is $3$ times that of BuAc, and that the

evaporation rate is considered constant, the time required for complete evaporation can be determined as the total volume

divided by the evaporation rate.

To prevent environmental contamination, there's no drain for the spilled gasoline. It simply evaporates, and the

recirculation ventilator of $300\frac{m^3}{m}in$ filters the air in the room using an $80\%$ efficient recirculation filter. No infiltration is

allowed for the same environmental reasons $($the room is hermetically sealed$).$

The team is concerned of:

Direct contact of humans to the gasoline on the floor.

The impact of gasoline vapors on the CEL $($ceiling exposure limit$).$ What is the reaction time for:

a$.$ A worker not wearing any PPE $($no mask$),$ who has a P$95$ mask available $($e$.$g$.,$ in their pocket$)$

b$.$ A worker continuously wearing a P$95$ mask $(95\%$ efficiency$)$

c$.$ A worker continuously wearing a P$100$ mask $(99\mathrm{.}97\%$ efficiency$)$

Note: P$100$ masks are oil$-$resistant and can be used in environments where oil$-$based particles are present. They

filter out $95\%($for P$95)$ or $99\mathrm{.}97\%($for P$100)$ of particles.

The concentration of gasoline vapors surpassing the LEL. To reduce the risk of an explosion, the team needs to

compute the reaction time, the time for which, under current configuration, the vapour concentration is below LEL.

This time is used to shut$-$down all the electronic and electrical equipment in the room and exit the room.

Any other risks to workers.

The duration required to safely re$-$access the room.

One solution is to change the ventilator in the current design and increase the $q1=$ recirculation ventilation speed.

a$.$ What should be the CFM of the new ventilator to avoid the above vapour$-$related risks $(2$ to $5)?$

b$.$ What is the maximum cost reasonably practicable for this ventilator?

ALARP values to consider for injuries in the table on the right.

Additional details:

Gasoline: molecular weight $=112\frac{g}{m}ol,$ liquid density $=714k\frac{g}{m^{{?}^{{?}^{?}}}}3$

Masimum Tolerable Risk $($per annum$).$

Employee

Pubic

Broadly Accepcable Risk $($per annum$)$

Employee and public

gasoline LEL $=1\mathrm{.}3\%,$ gasoline TWEL $=10$ PPM

$1$ mole volume at $0C=\frac{22\mathrm{.}41}{m}ol,$

${10}^{-3}{10}^{-4}$

gasoline STEL $=25PPM$ for $10$ minutes, gasoline C EL $=50PPM,$ value for $k($mixing factor$)=0\mathrm{.}4$

For simplicity, the room's pressure remains constant.

Present your findings in a table spanning $2$ hours post$-$incident. Compute data for each second from $0$ to $1$ minute and then

for every minute from $1$ to $120$ minutes.