Are you required to contribute to a firehouse mess fund as a condition of your employment and the funds are in the custody of your employer? If so, you would be able to deduct these meals. If the plan is voluntary, you would not be able to deduct the meals.
The key item here is whether the "chow fund" in mandatory as a condition of employment. If in is not mandatory, the meals will not be deductible.
The reference you need for this particular situation is SIBLA v. COMMISSIONER, 45 AFTR 2d 80-955 (611 F.2d 1260). In this case, the 9th circuit ruled the costs of meals for firefighter was only deductible if they were required to participate in a meal plan.